26 files changed, 5570 insertions, 0 deletions

diff --git a/liblogdiag/ld-canvas.c b/liblogdiag/ld-canvas.c
new file mode 100644
index 0000000..9523d9d
--- /dev/null
+++ b/liblogdiag/ld-canvas.c
@@ -0,0 +1,1417 @@
+/*
+ * ld-canvas.c
+ *
+ * This file is a part of logdiag.
+ * Copyright Přemysl Janouch 2010 - 2011. All rights reserved.
+ *
+ * See the file LICENSE for licensing information.
+ *
+ */
+
+#include <math.h>
+#include <string.h>
+#include <gdk/gdkkeysyms.h>
+
+#include "liblogdiag.h"
+#include "config.h"
+
+
+/**
+ * SECTION:ld-canvas
+ * @short_description: A canvas.
+ * @see_also: #LdDiagram
+ *
+ * #LdCanvas displays and enables the user to manipulate with an #LdDiagram.
+ */
+
+/* Milimetres per inch. */
+#define MM_PER_INCH 25.4
+/* The default screen resolution in DPI units. */
+#define DEFAULT_SCREEN_RESOLUTION 96
+
+/* The maximal, minimal and default values of zoom. */
+#define ZOOM_MIN 0.01
+#define ZOOM_MAX 100
+#define ZOOM_DEFAULT 1
+/* Multiplication factor for zooming with mouse wheel. */
+#define ZOOM_WHEEL_STEP 1.4
+
+/* When drawing is requested, extend all sides of
+ * the rectangle to be drawn by this number of pixels.
+ */
+#define QUEUE_DRAW_EXTEND 3
+/* Cursor tolerance for object borders. */
+#define OBJECT_BORDER_TOLERANCE 3
+/* Tolerance on all sides of symbols for strokes. */
+#define SYMBOL_CLIP_TOLERANCE 5
+
+/* Size of a highlighted terminal. */
+#define TERMINAL_RADIUS 5
+/* Tolerance around terminal points. */
+#define TERMINAL_HOVER_TOLERANCE 8
+
+/*
+ * OperationEnd:
+ *
+ * Called upon ending an operation.
+ */
+typedef void (*OperationEnd) (LdCanvas *self);
+
+enum
+{
+	OPER_0,
+	OPER_ADD_OBJECT
+};
+
+typedef struct _AddObjectData AddObjectData;
+
+struct _AddObjectData
+{
+	LdDiagramObject *object;
+	gboolean visible;
+};
+
+enum
+{
+	COLOR_BASE,
+	COLOR_GRID,
+	COLOR_OBJECT,
+	COLOR_SELECTION,
+	COLOR_TERMINAL,
+	COLOR_COUNT
+};
+
+typedef struct _LdCanvasColor LdCanvasColor;
+
+struct _LdCanvasColor
+{
+	gdouble r;
+	gdouble g;
+	gdouble b;
+	gdouble a;
+};
+
+/*
+ * LdCanvasPrivate:
+ * @diagram: A diagram object assigned to this canvas as a model.
+ * @library: A library object assigned to this canvas as a model.
+ * @adjustment_h: An adjustment object for the horizontal axis, if any.
+ * @adjustment_v: An adjustment object for the vertical axis, if any.
+ * @x: The X coordinate of the center of view.
+ * @y: The Y coordinate of the center of view.
+ * @zoom: The current zoom of the canvas.
+ * @operation: The current operation.
+ * @operation_data: Data related to the current operation.
+ * @operation_end: A callback to end the operation.
+ * @palette: Colors used by the widget.
+ */
+struct _LdCanvasPrivate
+{
+	LdDiagram *diagram;
+	LdLibrary *library;
+
+	GtkAdjustment *adjustment_h;
+	GtkAdjustment *adjustment_v;
+
+	gdouble x;
+	gdouble y;
+	gdouble zoom;
+
+	LdPoint terminal;
+	gboolean terminal_highlighted;
+
+	gint operation;
+	union
+	{
+		AddObjectData add_object;
+	}
+	operation_data;
+	OperationEnd operation_end;
+
+	LdCanvasColor palette[COLOR_COUNT];
+};
+
+#define OPER_DATA(self, member) ((self)->priv->operation_data.member)
+#define COLOR_GET(self, name) (&(self)->priv->palette[name])
+
+/*
+ * DrawData:
+ * @self: Our #LdCanvas.
+ * @cr: A cairo context to draw on.
+ * @exposed_rect: The area that is to be redrawn.
+ * @scale: Computed size of one diagram unit in pixels.
+ */
+typedef struct _DrawData DrawData;
+
+struct _DrawData
+{
+	LdCanvas *self;
+	cairo_t *cr;
+	LdRectangle exposed_rect;
+	gdouble scale;
+};
+
+enum
+{
+	PROP_0,
+	PROP_DIAGRAM,
+	PROP_LIBRARY,
+	PROP_ZOOM
+};
+
+static void ld_canvas_get_property (GObject *object, guint property_id,
+	GValue *value, GParamSpec *pspec);
+static void ld_canvas_set_property (GObject *object, guint property_id,
+	const GValue *value, GParamSpec *pspec);
+static void ld_canvas_finalize (GObject *gobject);
+
+static void ld_canvas_real_set_scroll_adjustments
+	(LdCanvas *self, GtkAdjustment *horizontal, GtkAdjustment *vertical);
+static void on_adjustment_value_changed
+	(GtkAdjustment *adjustment, LdCanvas *self);
+static void on_size_allocate (GtkWidget *widget, GtkAllocation *allocation,
+	gpointer user_data);
+static void update_adjustments (LdCanvas *self);
+
+static void diagram_connect_signals (LdCanvas *self);
+static void diagram_disconnect_signals (LdCanvas *self);
+
+static gdouble ld_canvas_get_base_unit_in_px (GtkWidget *self);
+static gdouble ld_canvas_get_scale_in_px (LdCanvas *self);
+
+static void simulate_motion (LdCanvas *self);
+static gboolean on_motion_notify (GtkWidget *widget, GdkEventMotion *event,
+	gpointer user_data);
+static gboolean on_leave_notify (GtkWidget *widget, GdkEventCrossing *event,
+	gpointer user_data);
+static gboolean on_button_press (GtkWidget *widget, GdkEventButton *event,
+	gpointer user_data);
+static gboolean on_button_release (GtkWidget *widget, GdkEventButton *event,
+	gpointer user_data);
+static gboolean on_scroll (GtkWidget *widget, GdkEventScroll *event,
+	gpointer user_data);
+
+static void ld_canvas_color_set (LdCanvasColor *color,
+	gdouble r, gdouble g, gdouble b, gdouble a);
+static void ld_canvas_color_apply (LdCanvasColor *color, cairo_t *cr);
+
+static void move_object_to_coords (LdCanvas *self, LdDiagramObject *object,
+	gdouble x, gdouble y);
+static LdDiagramObject *get_object_at_coords (LdCanvas *self,
+	gdouble x, gdouble y);
+static gboolean is_object_selected (LdCanvas *self, LdDiagramObject *object);
+static LdSymbol *resolve_diagram_symbol (LdCanvas *self,
+	LdDiagramSymbol *diagram_symbol);
+static gboolean get_symbol_area (LdCanvas *self, LdDiagramSymbol *symbol,
+	LdRectangle *rect);
+static gboolean get_symbol_clip_area (LdCanvas *self, LdDiagramSymbol *symbol,
+	LdRectangle *rect);
+static gboolean get_object_area (LdCanvas *self, LdDiagramObject *object,
+	LdRectangle *rect);
+static gboolean object_hit_test (LdCanvas *self, LdDiagramObject *object,
+	gdouble x, gdouble y);
+static void check_terminals (LdCanvas *self, gdouble x, gdouble y);
+static void hide_terminals (LdCanvas *self);
+static void queue_draw (LdCanvas *self, LdRectangle *rect);
+static void queue_object_draw (LdCanvas *self, LdDiagramObject *object);
+static void queue_terminal_draw (LdCanvas *self, LdPoint *terminal);
+
+static void ld_canvas_real_cancel_operation (LdCanvas *self);
+static void ld_canvas_add_object_end (LdCanvas *self);
+
+static gboolean on_expose_event (GtkWidget *widget, GdkEventExpose *event,
+	gpointer user_data);
+static void draw_grid (GtkWidget *widget, DrawData *data);
+static void draw_diagram (GtkWidget *widget, DrawData *data);
+static void draw_terminal (GtkWidget *widget, DrawData *data);
+static void draw_object (LdDiagramObject *diagram_object, DrawData *data);
+static void draw_symbol (LdDiagramSymbol *diagram_symbol, DrawData *data);
+
+
+G_DEFINE_TYPE (LdCanvas, ld_canvas, GTK_TYPE_DRAWING_AREA);
+
+static void
+ld_canvas_class_init (LdCanvasClass *klass)
+{
+	GObjectClass *object_class;
+	GtkWidgetClass *widget_class;
+	GtkBindingSet *binding_set;
+	GParamSpec *pspec;
+
+	widget_class = GTK_WIDGET_CLASS (klass);
+
+	object_class = G_OBJECT_CLASS (klass);
+	object_class->get_property = ld_canvas_get_property;
+	object_class->set_property = ld_canvas_set_property;
+	object_class->finalize = ld_canvas_finalize;
+
+	klass->set_scroll_adjustments = ld_canvas_real_set_scroll_adjustments;
+	klass->cancel_operation = ld_canvas_real_cancel_operation;
+
+	binding_set = gtk_binding_set_by_class (klass);
+	gtk_binding_entry_add_signal (binding_set, GDK_Escape, 0,
+		"cancel-operation", 0);
+
+/**
+ * LdCanvas:diagram:
+ *
+ * The underlying #LdDiagram object of this canvas.
+ */
+	pspec = g_param_spec_object ("diagram", "Diagram",
+		"The underlying diagram object of this canvas.",
+		LD_TYPE_DIAGRAM, G_PARAM_READWRITE);
+	g_object_class_install_property (object_class, PROP_DIAGRAM, pspec);
+
+/**
+ * LdCanvas:library:
+ *
+ * The #LdLibrary that this canvas retrieves symbols from.
+ */
+	pspec = g_param_spec_object ("library", "Library",
+		"The library that this canvas retrieves symbols from.",
+		LD_TYPE_LIBRARY, G_PARAM_READWRITE);
+	g_object_class_install_property (object_class, PROP_LIBRARY, pspec);
+
+/**
+ * LdCanvas:zoom:
+ *
+ * The zoom of this canvas.
+ */
+	pspec = g_param_spec_double ("zoom", "Zoom",
+		"The zoom of this canvas.",
+		ZOOM_MIN, ZOOM_MAX, ZOOM_DEFAULT, G_PARAM_READWRITE);
+	g_object_class_install_property (object_class, PROP_ZOOM, pspec);
+
+/**
+ * LdCanvas::set-scroll-adjustments:
+ * @horizontal: The horizontal #GtkAdjustment.
+ * @vertical: The vertical #GtkAdjustment.
+ *
+ * Set scroll adjustments for the canvas.
+ */
+	widget_class->set_scroll_adjustments_signal = g_signal_new
+		("set-scroll-adjustments", G_TYPE_FROM_CLASS (widget_class),
+		G_SIGNAL_RUN_LAST | G_SIGNAL_ACTION,
+		G_STRUCT_OFFSET (LdCanvasClass, set_scroll_adjustments),
+		NULL, NULL,
+		g_cclosure_user_marshal_VOID__OBJECT_OBJECT,
+		G_TYPE_NONE, 2, GTK_TYPE_ADJUSTMENT, GTK_TYPE_ADJUSTMENT);
+
+/**
+ * LdCanvas::cancel-operation:
+ *
+ * Cancel any current operation.
+ */
+	klass->cancel_operation_signal = g_signal_new
+		("cancel-operation", G_TYPE_FROM_CLASS (klass),
+		G_SIGNAL_RUN_LAST | G_SIGNAL_ACTION,
+		G_STRUCT_OFFSET (LdCanvasClass, cancel_operation), NULL, NULL,
+		g_cclosure_marshal_VOID__VOID,
+		G_TYPE_NONE, 0);
+
+	g_type_class_add_private (klass, sizeof (LdCanvasPrivate));
+}
+
+static void
+ld_canvas_init (LdCanvas *self)
+{
+	self->priv = G_TYPE_INSTANCE_GET_PRIVATE
+		(self, LD_TYPE_CANVAS, LdCanvasPrivate);
+
+	self->priv->x = 0;
+	self->priv->y = 0;
+	self->priv->zoom = ZOOM_DEFAULT;
+
+	ld_canvas_color_set (COLOR_GET (self, COLOR_BASE), 1, 1, 1, 1);
+	ld_canvas_color_set (COLOR_GET (self, COLOR_GRID), 0.5, 0.5, 0.5, 1);
+	ld_canvas_color_set (COLOR_GET (self, COLOR_OBJECT), 0, 0, 0, 1);
+	ld_canvas_color_set (COLOR_GET (self, COLOR_SELECTION), 0, 0, 1, 1);
+	ld_canvas_color_set (COLOR_GET (self, COLOR_TERMINAL), 1, 0.5, 0.5, 1);
+
+	g_signal_connect (self, "size-allocate",
+		G_CALLBACK (on_size_allocate), NULL);
+	g_signal_connect (self, "expose-event",
+		G_CALLBACK (on_expose_event), NULL);
+
+	g_signal_connect (self, "motion-notify-event",
+		G_CALLBACK (on_motion_notify), NULL);
+	g_signal_connect (self, "leave-notify-event",
+		G_CALLBACK (on_leave_notify), NULL);
+	g_signal_connect (self, "button-press-event",
+		G_CALLBACK (on_button_press), NULL);
+	g_signal_connect (self, "button-release-event",
+		G_CALLBACK (on_button_release), NULL);
+	g_signal_connect (self, "scroll-event",
+		G_CALLBACK (on_scroll), NULL);
+
+	g_object_set (self, "can-focus", TRUE, NULL);
+
+	gtk_widget_add_events (GTK_WIDGET (self),
+		GDK_POINTER_MOTION_MASK | GDK_POINTER_MOTION_HINT_MASK
+		| GDK_BUTTON_PRESS_MASK | GDK_BUTTON_RELEASE_MASK
+		| GDK_LEAVE_NOTIFY_MASK);
+}
+
+static void
+ld_canvas_finalize (GObject *gobject)
+{
+	LdCanvas *self;
+
+	self = LD_CANVAS (gobject);
+
+	ld_canvas_real_set_scroll_adjustments (self, NULL, NULL);
+
+	if (self->priv->diagram)
+	{
+		diagram_disconnect_signals (self);
+		g_object_unref (self->priv->diagram);
+	}
+	if (self->priv->library)
+		g_object_unref (self->priv->library);
+
+	/* Chain up to the parent class. */
+	G_OBJECT_CLASS (ld_canvas_parent_class)->finalize (gobject);
+}
+
+static void
+ld_canvas_get_property (GObject *object, guint property_id,
+	GValue *value, GParamSpec *pspec)
+{
+	LdCanvas *self;
+
+	self = LD_CANVAS (object);
+	switch (property_id)
+	{
+	case PROP_DIAGRAM:
+		g_value_set_object (value, ld_canvas_get_diagram (self));
+		break;
+	case PROP_LIBRARY:
+		g_value_set_object (value, ld_canvas_get_library (self));
+		break;
+	case PROP_ZOOM:
+		g_value_set_double (value, ld_canvas_get_zoom (self));
+		break;
+	default:
+		G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
+	}
+}
+
+static void
+ld_canvas_set_property (GObject *object, guint property_id,
+	const GValue *value, GParamSpec *pspec)
+{
+	LdCanvas *self;
+
+	self = LD_CANVAS (object);
+	switch (property_id)
+	{
+	case PROP_DIAGRAM:
+		ld_canvas_set_diagram (self, LD_DIAGRAM (g_value_get_object (value)));
+		break;
+	case PROP_LIBRARY:
+		ld_canvas_set_library (self, LD_LIBRARY (g_value_get_object (value)));
+		break;
+	case PROP_ZOOM:
+		ld_canvas_set_zoom (self, g_value_get_double (value));
+		break;
+	default:
+		G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
+	}
+}
+
+static void
+ld_canvas_real_set_scroll_adjustments (LdCanvas *self,
+	GtkAdjustment *horizontal, GtkAdjustment *vertical)
+{
+	/* TODO: Infinite canvas. */
+	GtkWidget *widget;
+	gdouble scale;
+
+	widget = GTK_WIDGET (self);
+	scale = ld_canvas_get_scale_in_px (self);
+
+	if (horizontal != self->priv->adjustment_h)
+	{
+		if (self->priv->adjustment_h)
+		{
+			g_signal_handlers_disconnect_by_func (self->priv->adjustment_h,
+				on_adjustment_value_changed, self);
+			g_object_unref (self->priv->adjustment_h);
+
+			self->priv->adjustment_h = NULL;
+		}
+		if (horizontal)
+		{
+			g_object_ref (horizontal);
+			g_signal_connect (horizontal, "value-changed",
+				G_CALLBACK (on_adjustment_value_changed), self);
+
+			horizontal->upper = 100;
+			horizontal->lower = -100;
+			horizontal->step_increment = 0.5;
+			horizontal->page_increment = 5;
+			horizontal->page_size = widget->allocation.width / scale;
+			horizontal->value = -horizontal->page_size / 2;
+
+			self->priv->adjustment_h = horizontal;
+		}
+	}
+
+	if (vertical != self->priv->adjustment_v)
+	{
+		if (self->priv->adjustment_v)
+		{
+			g_signal_handlers_disconnect_by_func (self->priv->adjustment_v,
+				on_adjustment_value_changed, self);
+			g_object_unref (self->priv->adjustment_v);
+
+			self->priv->adjustment_v = NULL;
+		}
+		if (vertical)
+		{
+			g_object_ref (vertical);
+			g_signal_connect (vertical, "value-changed",
+				G_CALLBACK (on_adjustment_value_changed), self);
+
+			vertical->upper = 100;
+			vertical->lower = -100;
+			vertical->step_increment = 0.5;
+			vertical->page_increment = 5;
+			vertical->page_size = widget->allocation.height / scale;
+			vertical->value = -vertical->page_size / 2;
+
+			self->priv->adjustment_v = vertical;
+		}
+	}
+}
+
+static void
+on_adjustment_value_changed (GtkAdjustment *adjustment, LdCanvas *self)
+{
+	GtkWidget *widget;
+	gdouble scale;
+
+	widget = GTK_WIDGET (self);
+	scale = ld_canvas_get_scale_in_px (self);
+
+	if (adjustment == self->priv->adjustment_h)
+	{
+		self->priv->x = adjustment->value
+			+ widget->allocation.width / scale / 2;
+		gtk_widget_queue_draw (widget);
+	}
+	else if (adjustment == self->priv->adjustment_v)
+	{
+		self->priv->y = adjustment->value
+			+ widget->allocation.height / scale / 2;
+		gtk_widget_queue_draw (widget);
+	}
+}
+
+static void
+on_size_allocate (GtkWidget *widget, GtkAllocation *allocation,
+	gpointer user_data)
+{
+	LdCanvas *self;
+
+	self = LD_CANVAS (widget);
+
+	/* FIXME: If the new allocation is bigger, we may see more than
+	 *        what we're supposed to be able to see -> adjust X and Y.
+	 *
+	 *        If the visible area is so large that we simply must see more,
+	 *        let's disable the scrollbars in question.
+	 */
+	update_adjustments (self);
+}
+
+static void
+update_adjustments (LdCanvas *self)
+{
+	gdouble scale;
+
+	scale = ld_canvas_get_scale_in_px (self);
+
+	if (self->priv->adjustment_h)
+	{
+		self->priv->adjustment_h->page_size
+			= GTK_WIDGET (self)->allocation.width  / scale;
+		self->priv->adjustment_h->value
+			= self->priv->x - self->priv->adjustment_h->page_size / 2;
+		gtk_adjustment_changed (self->priv->adjustment_h);
+	}
+	if (self->priv->adjustment_v)
+	{
+		self->priv->adjustment_v->page_size
+			= GTK_WIDGET (self)->allocation.height / scale;
+		self->priv->adjustment_v->value
+			= self->priv->y - self->priv->adjustment_v->page_size / 2;
+		gtk_adjustment_changed (self->priv->adjustment_v);
+	}
+}
+
+
+/* ===== Generic interface etc. ============================================ */
+
+/**
+ * ld_canvas_new:
+ *
+ * Create an instance.
+ */
+LdCanvas *
+ld_canvas_new (void)
+{
+	return g_object_new (LD_TYPE_CANVAS, NULL);
+}
+
+/**
+ * ld_canvas_set_diagram:
+ * @self: An #LdCanvas object.
+ * @diagram: The #LdDiagram to be assigned to the canvas.
+ *
+ * Assign an #LdDiagram object to the canvas.
+ */
+void
+ld_canvas_set_diagram (LdCanvas *self, LdDiagram *diagram)
+{
+	g_return_if_fail (LD_IS_CANVAS (self));
+	g_return_if_fail (LD_IS_DIAGRAM (diagram));
+
+	if (self->priv->diagram)
+	{
+		diagram_disconnect_signals (self);
+		g_object_unref (self->priv->diagram);
+	}
+
+	self->priv->diagram = diagram;
+	diagram_connect_signals (self);
+	g_object_ref (diagram);
+
+	g_object_notify (G_OBJECT (self), "diagram");
+}
+
+/**
+ * ld_canvas_get_diagram:
+ * @self: An #LdCanvas object.
+ *
+ * Get the #LdDiagram object assigned to this canvas.
+ * The reference count on the diagram is not incremented.
+ */
+LdDiagram *
+ld_canvas_get_diagram (LdCanvas *self)
+{
+	g_return_val_if_fail (LD_IS_CANVAS (self), NULL);
+	return self->priv->diagram;
+}
+
+static void
+diagram_connect_signals (LdCanvas *self)
+{
+	g_return_if_fail (LD_IS_DIAGRAM (self->priv->diagram));
+
+	g_signal_connect_swapped (self->priv->diagram, "changed",
+		G_CALLBACK (gtk_widget_queue_draw), self);
+	g_signal_connect_swapped (self->priv->diagram, "selection-changed",
+		G_CALLBACK (gtk_widget_queue_draw), self);
+}
+
+static void
+diagram_disconnect_signals (LdCanvas *self)
+{
+	g_return_if_fail (LD_IS_DIAGRAM (self->priv->diagram));
+
+	g_signal_handlers_disconnect_matched (self->priv->diagram,
+		G_SIGNAL_MATCH_FUNC | G_SIGNAL_MATCH_DATA, 0, 0, NULL,
+		gtk_widget_queue_draw, self);
+}
+
+/**
+ * ld_canvas_set_library:
+ * @self: An #LdCanvas object.
+ * @library: The #LdLibrary to be assigned to the canvas.
+ *
+ * Assign an #LdLibrary object to the canvas.
+ */
+void
+ld_canvas_set_library (LdCanvas *self, LdLibrary *library)
+{
+	g_return_if_fail (LD_IS_CANVAS (self));
+	g_return_if_fail (LD_IS_LIBRARY (library));
+
+	if (self->priv->library)
+		g_object_unref (self->priv->library);
+
+	self->priv->library = library;
+	g_object_ref (library);
+
+	g_object_notify (G_OBJECT (self), "library");
+}
+
+/**
+ * ld_canvas_get_library:
+ * @self: An #LdCanvas object.
+ *
+ * Get the #LdLibrary object assigned to this canvas.
+ * The reference count on the library is not incremented.
+ */
+LdLibrary *
+ld_canvas_get_library (LdCanvas *self)
+{
+	g_return_val_if_fail (LD_IS_CANVAS (self), NULL);
+	return self->priv->library;
+}
+
+/*
+ * ld_canvas_get_base_unit_in_px:
+ * @self: A #GtkWidget object to retrieve DPI from (indirectly).
+ *
+ * Return value: Length of the base unit in pixels.
+ */
+static gdouble
+ld_canvas_get_base_unit_in_px (GtkWidget *self)
+{
+	gdouble resolution;
+
+	g_return_val_if_fail (GTK_IS_WIDGET (self), 1);
+
+	resolution = gdk_screen_get_resolution (gtk_widget_get_screen (self));
+	if (resolution == -1)
+		resolution = DEFAULT_SCREEN_RESOLUTION;
+
+	/* XXX: It might look better if the unit was rounded to a whole number. */
+	return resolution / MM_PER_INCH * LD_CANVAS_BASE_UNIT_LENGTH;
+}
+
+/*
+ * ld_canvas_get_scale_in_px:
+ * @self: An #LdCanvas object.
+ *
+ * Return value: Displayed length of the base unit in pixels.
+ */
+static gdouble
+ld_canvas_get_scale_in_px (LdCanvas *self)
+{
+	g_return_val_if_fail (LD_IS_CANVAS (self), 1);
+
+	return ld_canvas_get_base_unit_in_px (GTK_WIDGET (self))
+		* self->priv->zoom;
+}
+
+/**
+ * ld_canvas_widget_to_diagram_coords:
+ * @self: An #LdCanvas object.
+ * @wx: The X coordinate to be translated.
+ * @wy: The Y coordinate to be translated.
+ * @dx: (out): The translated X coordinate.
+ * @dy: (out): The translated Y coordinate.
+ *
+ * Translate coordinates located inside the canvas window
+ * into diagram coordinates.
+ */
+void
+ld_canvas_widget_to_diagram_coords (LdCanvas *self,
+	gdouble wx, gdouble wy, gdouble *dx, gdouble *dy)
+{
+	GtkWidget *widget;
+	gdouble scale;
+
+	g_return_if_fail (LD_IS_CANVAS (self));
+	g_return_if_fail (dx != NULL);
+	g_return_if_fail (dy != NULL);
+
+	widget = GTK_WIDGET (self);
+	scale = ld_canvas_get_scale_in_px (self);
+
+	/* We know diagram coordinates of the center of the canvas, so we may
+	 * translate the given X and Y coordinates to this center and then scale
+	 * them by dividing them by the current scale.
+	 */
+	*dx = self->priv->x + (wx - (widget->allocation.width  * 0.5)) / scale;
+	*dy = self->priv->y + (wy - (widget->allocation.height * 0.5)) / scale;
+}
+
+/**
+ * ld_canvas_diagram_to_widget_coords:
+ * @self: An #LdCanvas object.
+ * @dx: The X coordinate to be translated.
+ * @dy: The Y coordinate to be translated.
+ * @wx: (out): The translated X coordinate.
+ * @wy: (out): The translated Y coordinate.
+ *
+ * Translate diagram coordinates into canvas coordinates.
+ */
+void
+ld_canvas_diagram_to_widget_coords (LdCanvas *self,
+	gdouble dx, gdouble dy, gdouble *wx, gdouble *wy)
+{
+	GtkWidget *widget;
+	gdouble scale;
+
+	g_return_if_fail (LD_IS_CANVAS (self));
+	g_return_if_fail (wx != NULL);
+	g_return_if_fail (wy != NULL);
+
+	widget = GTK_WIDGET (self);
+	scale = ld_canvas_get_scale_in_px (self);
+
+	/* Just the reversal of ld_canvas_widget_to_diagram_coords(). */
+	*wx = scale * (dx - self->priv->x) + 0.5 * widget->allocation.width;
+	*wy = scale * (dy - self->priv->y) + 0.5 * widget->allocation.height;
+}
+
+/**
+ * ld_canvas_get_zoom:
+ * @self: An #LdCanvas object.
+ *
+ * Return value: Zoom of the canvas.
+ */
+gdouble
+ld_canvas_get_zoom (LdCanvas *self)
+{
+	g_return_val_if_fail (LD_IS_CANVAS (self), -1);
+	return self->priv->zoom;
+}
+
+/**
+ * ld_canvas_set_zoom:
+ * @self: An #LdCanvas object.
+ * @zoom: The zoom.
+ *
+ * Set zoom of the canvas.
+ */
+void
+ld_canvas_set_zoom (LdCanvas *self, gdouble zoom)
+{
+	gdouble clamped_zoom;
+
+	g_return_if_fail (LD_IS_CANVAS (self));
+
+	clamped_zoom = CLAMP (zoom, ZOOM_MIN, ZOOM_MAX);
+	if (self->priv->zoom == clamped_zoom)
+		return;
+
+	self->priv->zoom = clamped_zoom;
+
+	simulate_motion (self);
+	update_adjustments (self);
+	gtk_widget_queue_draw (GTK_WIDGET (self));
+
+	g_object_notify (G_OBJECT (self), "zoom");
+}
+
+
+/* ===== Operations ======================================================== */
+
+static void
+ld_canvas_real_cancel_operation (LdCanvas *self)
+{
+	g_return_if_fail (LD_IS_CANVAS (self));
+
+	if (self->priv->operation)
+	{
+		if (self->priv->operation_end)
+			self->priv->operation_end (self);
+		self->priv->operation = OPER_0;
+		self->priv->operation_end = NULL;
+	}
+}
+
+/**
+ * ld_canvas_add_object_begin:
+ * @self: An #LdCanvas object.
+ * @object: (transfer full): The object to be added to the diagram.
+ *
+ * Begin an operation for adding an object into the diagram.
+ */
+void
+ld_canvas_add_object_begin (LdCanvas *self, LdDiagramObject *object)
+{
+	AddObjectData *data;
+
+	g_return_if_fail (LD_IS_CANVAS (self));
+	g_return_if_fail (LD_IS_DIAGRAM_OBJECT (object));
+
+	ld_canvas_real_cancel_operation (self);
+
+	self->priv->operation = OPER_ADD_OBJECT;
+	self->priv->operation_end = ld_canvas_add_object_end;
+
+	data = &OPER_DATA (self, add_object);
+	data->object = object;
+}
+
+static void
+ld_canvas_add_object_end (LdCanvas *self)
+{
+	AddObjectData *data;
+
+	data = &OPER_DATA (self, add_object);
+	if (data->object)
+	{
+		queue_object_draw (self, data->object);
+		g_object_unref (data->object);
+		data->object = NULL;
+	}
+}
+
+
+/* ===== Events, rendering ================================================= */
+
+static void
+ld_canvas_color_set (LdCanvasColor *color,
+	gdouble r, gdouble g, gdouble b, gdouble a)
+{
+	color->r = r;
+	color->g = g;
+	color->b = b;
+	color->a = a;
+}
+
+static void
+ld_canvas_color_apply (LdCanvasColor *color, cairo_t *cr)
+{
+	cairo_set_source_rgba (cr, color->r, color->g, color->b, color->a);
+}
+
+static void
+move_object_to_coords (LdCanvas *self, LdDiagramObject *object,
+	gdouble x, gdouble y)
+{
+	gdouble dx, dy;
+
+	ld_canvas_widget_to_diagram_coords (self, x, y, &dx, &dy);
+	ld_diagram_object_set_x (object, floor (dx + 0.5));
+	ld_diagram_object_set_y (object, floor (dy + 0.5));
+}
+
+static LdDiagramObject *
+get_object_at_coords (LdCanvas *self, gdouble x, gdouble y)
+{
+	GList *objects, *iter;
+
+	/* Iterate from the top object downwards. */
+	objects = (GList *) ld_diagram_get_objects (self->priv->diagram);
+	for (iter = objects; iter; iter = g_list_next (iter))
+	{
+		LdDiagramObject *object;
+
+		object = LD_DIAGRAM_OBJECT (iter->data);
+		if (object_hit_test (self, object, x, y))
+			return object;
+	}
+	return NULL;
+}
+
+static gboolean
+is_object_selected (LdCanvas *self, LdDiagramObject *object)
+{
+	return g_list_find (ld_diagram_get_selection (self->priv->diagram),
+		object) != NULL;
+}
+
+static LdSymbol *
+resolve_diagram_symbol (LdCanvas *self, LdDiagramSymbol *diagram_symbol)
+{
+	if (!self->priv->library)
+		return NULL;
+
+	return ld_library_find_symbol (self->priv->library,
+		ld_diagram_symbol_get_class (diagram_symbol));
+}
+
+static gboolean
+get_symbol_area (LdCanvas *self, LdDiagramSymbol *symbol, LdRectangle *rect)
+{
+	LdDiagramObject *object;
+	gdouble object_x, object_y;
+	LdSymbol *library_symbol;
+	LdRectangle area;
+	gdouble x1, x2;
+	gdouble y1, y2;
+
+	object = LD_DIAGRAM_OBJECT (symbol);
+	object_x = ld_diagram_object_get_x (object);
+	object_y = ld_diagram_object_get_y (object);
+
+	library_symbol = resolve_diagram_symbol (self, symbol);
+	if (library_symbol)
+		ld_symbol_get_area (library_symbol, &area);
+	else
+		return FALSE;
+
+	/* TODO: Rotate the rectangle for other orientations. */
+	ld_canvas_diagram_to_widget_coords (self,
+		object_x + area.x,
+		object_y + area.y,
+		&x1, &y1);
+	ld_canvas_diagram_to_widget_coords (self,
+		object_x + area.x + area.width,
+		object_y + area.y + area.height,
+		&x2, &y2);
+
+	rect->x = x1;
+	rect->y = y1;
+	rect->width  = x2 - x1;
+	rect->height = y2 - y1;
+	return TRUE;
+}
+
+static gboolean
+get_symbol_clip_area (LdCanvas *self, LdDiagramSymbol *symbol,
+	LdRectangle *rect)
+{
+	LdRectangle object_rect;
+
+	if (!get_object_area (self, LD_DIAGRAM_OBJECT (symbol), &object_rect))
+		return FALSE;
+
+	*rect = object_rect;
+	ld_rectangle_extend (rect, SYMBOL_CLIP_TOLERANCE);
+	return TRUE;
+}
+
+static gboolean
+get_object_area (LdCanvas *self, LdDiagramObject *object, LdRectangle *rect)
+{
+	if (LD_IS_DIAGRAM_SYMBOL (object))
+		return get_symbol_area (self, LD_DIAGRAM_SYMBOL (object), rect);
+	return FALSE;
+}
+
+static gboolean
+object_hit_test (LdCanvas *self, LdDiagramObject *object, gdouble x, gdouble y)
+{
+	LdRectangle rect;
+
+	if (!get_object_area (self, object, &rect))
+		return FALSE;
+	ld_rectangle_extend (&rect, OBJECT_BORDER_TOLERANCE);
+	return ld_rectangle_contains (&rect, x, y);
+}
+
+static void
+check_terminals (LdCanvas *self, gdouble x, gdouble y)
+{
+	GList *objects, *iter;
+	LdDiagramSymbol *closest_symbol = NULL;
+	gdouble closest_distance = TERMINAL_HOVER_TOLERANCE;
+	LdPoint closest_terminal;
+
+	objects = (GList *) ld_diagram_get_objects (self->priv->diagram);
+	for (iter = objects; iter; iter = g_list_next (iter))
+	{
+		LdDiagramObject *diagram_object;
+		gdouble object_x, object_y;
+		LdDiagramSymbol *diagram_symbol;
+		LdSymbol *symbol;
+		const LdPointArray *terminals;
+		gint i;
+
+		if (!LD_IS_DIAGRAM_SYMBOL (iter->data))
+			continue;
+
+		diagram_symbol = LD_DIAGRAM_SYMBOL (iter->data);
+		symbol = resolve_diagram_symbol (self, diagram_symbol);
+		if (!symbol)
+			continue;
+
+		diagram_object = LD_DIAGRAM_OBJECT (iter->data);
+		object_x = ld_diagram_object_get_x (diagram_object);
+		object_y = ld_diagram_object_get_y (diagram_object);
+
+		terminals = ld_symbol_get_terminals (symbol);
+
+		for (i = 0; i < terminals->num_points; i++)
+		{
+			LdPoint cur_term;
+			gdouble distance;
+
+			cur_term = terminals->points[i];
+			cur_term.x += object_x;
+			cur_term.y += object_y;
+			ld_canvas_diagram_to_widget_coords (self,
+				cur_term.x, cur_term.y, &cur_term.x, &cur_term.y);
+
+			distance = ld_point_distance (&cur_term, x, y);
+			if (distance <= closest_distance)
+			{
+				closest_symbol = diagram_symbol;
+				closest_distance = distance;
+				closest_terminal = cur_term;
+			}
+		}
+	}
+
+	hide_terminals (self);
+
+	if (closest_symbol)
+	{
+		self->priv->terminal_highlighted = TRUE;
+		self->priv->terminal = closest_terminal;
+		queue_terminal_draw (self, &closest_terminal);
+	}
+}
+
+static void
+hide_terminals (LdCanvas *self)
+{
+	if (self->priv->terminal_highlighted)
+	{
+		self->priv->terminal_highlighted = FALSE;
+		queue_terminal_draw (self, &self->priv->terminal);
+	}
+}
+
+static void
+queue_draw (LdCanvas *self, LdRectangle *rect)
+{
+	LdRectangle area;
+
+	area = *rect;
+	ld_rectangle_extend (&area, QUEUE_DRAW_EXTEND);
+	gtk_widget_queue_draw_area (GTK_WIDGET (self),
+		area.x, area.y, area.width, area.height);
+}
+
+static void
+queue_object_draw (LdCanvas *self, LdDiagramObject *object)
+{
+	if (LD_IS_DIAGRAM_SYMBOL (object))
+	{
+		LdRectangle rect;
+
+		if (!get_symbol_clip_area (self, LD_DIAGRAM_SYMBOL (object), &rect))
+			return;
+		queue_draw (self, &rect);
+	}
+}
+
+static void
+queue_terminal_draw (LdCanvas *self, LdPoint *terminal)
+{
+	LdRectangle rect;
+
+	rect.x = terminal->x - TERMINAL_RADIUS;
+	rect.y = terminal->y - TERMINAL_RADIUS;
+	rect.width  = 2 * TERMINAL_RADIUS;
+	rect.height = 2 * TERMINAL_RADIUS;
+	queue_draw (self, &rect);
+}
+
+static void
+simulate_motion (LdCanvas *self)
+{
+	GdkEventMotion event;
+	GtkWidget *widget;
+	gint x, y;
+	GdkModifierType state;
+
+	widget = GTK_WIDGET (self);
+
+	if (gdk_window_get_pointer (widget->window, &x, &y, &state)
+		!= widget->window)
+		return;
+
+	memset (&event, 0, sizeof (event));
+	event.type = GDK_MOTION_NOTIFY;
+	event.window = widget->window;
+	event.x = x;
+	event.y = y;
+	event.state = state;
+
+	on_motion_notify (widget, &event, NULL);
+}
+
+static gboolean
+on_motion_notify (GtkWidget *widget, GdkEventMotion *event, gpointer user_data)
+{
+	LdCanvas *self;
+
+	self = LD_CANVAS (widget);
+	switch (self->priv->operation)
+	{
+		AddObjectData *data;
+
+	case OPER_ADD_OBJECT:
+		data = &OPER_DATA (self, add_object);
+		data->visible = TRUE;
+
+		queue_object_draw (self, data->object);
+		move_object_to_coords (self, data->object, event->x, event->y);
+		queue_object_draw (self, data->object);
+		break;
+	case OPER_0:
+		check_terminals (self, event->x, event->y);
+		break;
+	}
+	return FALSE;
+}
+
+static gboolean
+on_leave_notify (GtkWidget *widget, GdkEventCrossing *event, gpointer user_data)
+{
+	LdCanvas *self;
+
+	self = LD_CANVAS (widget);
+	switch (self->priv->operation)
+	{
+		AddObjectData *data;
+
+	case OPER_ADD_OBJECT:
+		data = &OPER_DATA (self, add_object);
+		data->visible = FALSE;
+
+		queue_object_draw (self, data->object);
+		break;
+	}
+	return FALSE;
+}
+
+static gboolean
+on_button_press (GtkWidget *widget, GdkEventButton *event, gpointer user_data)
+{
+	LdCanvas *self;
+
+	if (!gtk_widget_has_focus (widget))
+		gtk_widget_grab_focus (widget);
+
+	self = LD_CANVAS (widget);
+	switch (self->priv->operation)
+	{
+		AddObjectData *data;
+
+	case OPER_ADD_OBJECT:
+		data = &OPER_DATA (self, add_object);
+
+		queue_object_draw (self, data->object);
+		move_object_to_coords (self, data->object, event->x, event->y);
+
+		if (self->priv->diagram)
+			ld_diagram_insert_object (self->priv->diagram, data->object, 0);
+
+		/* XXX: "cancel" causes confusion. */
+		ld_canvas_real_cancel_operation (self);
+		break;
+	case OPER_0:
+		if (self->priv->diagram)
+		{
+			LdDiagramObject *object;
+
+			if (event->state != GDK_SHIFT_MASK)
+				ld_diagram_unselect_all (self->priv->diagram);
+
+			object = get_object_at_coords (self, event->x, event->y);
+			if (object)
+				ld_diagram_selection_add (self->priv->diagram, object, 0);
+		}
+		break;
+	}
+	return FALSE;
+}
+
+static gboolean
+on_button_release (GtkWidget *widget, GdkEventButton *event, gpointer user_data)
+{
+	return FALSE;
+}
+
+static gboolean
+on_scroll (GtkWidget *widget, GdkEventScroll *event, gpointer user_data)
+{
+	gdouble prev_x, prev_y;
+	gdouble new_x, new_y;
+	LdCanvas *self;
+
+	self = LD_CANVAS (widget);
+
+	ld_canvas_widget_to_diagram_coords (self,
+		event->x, event->y, &prev_x, &prev_y);
+
+	switch (event->direction)
+	{
+	case GDK_SCROLL_UP:
+		ld_canvas_set_zoom (self, self->priv->zoom * ZOOM_WHEEL_STEP);
+		break;
+	case GDK_SCROLL_DOWN:
+		ld_canvas_set_zoom (self, self->priv->zoom / ZOOM_WHEEL_STEP);
+		break;
+	default:
+		return FALSE;
+	}
+
+	ld_canvas_widget_to_diagram_coords (self,
+		event->x, event->y, &new_x, &new_y);
+
+	/* Focus on the point under the cursor. */
+	self->priv->x += prev_x - new_x;
+	self->priv->y += prev_y - new_y;
+
+	check_terminals (self, event->x, event->y);
+	return TRUE;
+}
+
+static gboolean
+on_expose_event (GtkWidget *widget, GdkEventExpose *event, gpointer user_data)
+{
+	DrawData data;
+
+	data.cr = gdk_cairo_create (widget->window);
+	data.self = LD_CANVAS (widget);
+	data.scale = ld_canvas_get_scale_in_px (data.self);
+	data.exposed_rect.x = event->area.x;
+	data.exposed_rect.y = event->area.y;
+	data.exposed_rect.width = event->area.width;
+	data.exposed_rect.height = event->area.height;
+
+	gdk_cairo_rectangle (data.cr, &event->area);
+	cairo_clip (data.cr);
+
+	ld_canvas_color_apply (COLOR_GET (data.self, COLOR_BASE), data.cr);
+	cairo_paint (data.cr);
+
+	draw_grid (widget, &data);
+	draw_diagram (widget, &data);
+	draw_terminal (widget, &data);
+
+	cairo_destroy (data.cr);
+	return FALSE;
+}
+
+static void
+draw_grid (GtkWidget *widget, DrawData *data)
+{
+	gdouble grid_step;
+	gdouble x_init, y_init;
+	gdouble x, y;
+
+	grid_step = data->scale;
+	while (grid_step < 5)
+		grid_step *= 5;
+
+	ld_canvas_color_apply (COLOR_GET (data->self, COLOR_GRID), data->cr);
+	cairo_set_line_width (data->cr, 1);
+	cairo_set_line_cap (data->cr, CAIRO_LINE_CAP_ROUND);
+
+	/* Get coordinates of the top-left point. */
+	ld_canvas_widget_to_diagram_coords (data->self,
+		data->exposed_rect.x, data->exposed_rect.y, &x_init, &y_init);
+	ld_canvas_diagram_to_widget_coords (data->self,
+		ceil (x_init), ceil (y_init), &x_init, &y_init);
+
+	/* Iterate over all the points. */
+	for     (x = x_init; x <= data->exposed_rect.x + data->exposed_rect.width;
+			 x += grid_step)
+	{
+		for (y = y_init; y <= data->exposed_rect.y + data->exposed_rect.height;
+			 y += grid_step)
+		{
+			cairo_move_to (data->cr, x, y);
+			cairo_line_to (data->cr, x, y);
+		}
+	}
+	cairo_stroke (data->cr);
+}
+
+static void
+draw_terminal (GtkWidget *widget, DrawData *data)
+{
+	LdCanvasPrivate *priv;
+
+	priv = data->self->priv;
+	if (!priv->terminal_highlighted)
+		return;
+
+	ld_canvas_color_apply (COLOR_GET (data->self, COLOR_TERMINAL), data->cr);
+	cairo_set_line_width (data->cr, 1);
+
+	cairo_new_path (data->cr);
+	cairo_arc (data->cr, priv->terminal.x, priv->terminal.y,
+		TERMINAL_RADIUS, 0, 2 * G_PI);
+	cairo_stroke (data->cr);
+}
+
+static void
+draw_diagram (GtkWidget *widget, DrawData *data)
+{
+	GList *objects, *iter;
+
+	if (!data->self->priv->diagram)
+		return;
+
+	cairo_save (data->cr);
+	cairo_set_line_width (data->cr, 1 / data->scale);
+
+	/* Draw objects from the diagram, from bottom to top. */
+	objects = (GList *) ld_diagram_get_objects (data->self->priv->diagram);
+	for (iter = g_list_last (objects); iter; iter = g_list_previous (iter))
+		draw_object (LD_DIAGRAM_OBJECT (iter->data), data);
+
+	switch (data->self->priv->operation)
+	{
+		AddObjectData *op_data;
+
+	case OPER_ADD_OBJECT:
+		op_data = &OPER_DATA (data->self, add_object);
+		if (op_data->visible)
+			draw_object (op_data->object, data);
+		break;
+	}
+
+	cairo_restore (data->cr);
+}
+
+static void
+draw_object (LdDiagramObject *diagram_object, DrawData *data)
+{
+	g_return_if_fail (LD_IS_DIAGRAM_OBJECT (diagram_object));
+	g_return_if_fail (data != NULL);
+
+	if (is_object_selected (data->self, diagram_object))
+		ld_canvas_color_apply (COLOR_GET (data->self,
+			COLOR_SELECTION), data->cr);
+	else
+		ld_canvas_color_apply (COLOR_GET (data->self,
+			COLOR_OBJECT), data->cr);
+
+	if (LD_IS_DIAGRAM_SYMBOL (diagram_object))
+		draw_symbol (LD_DIAGRAM_SYMBOL (diagram_object), data);
+}
+
+static void
+draw_symbol (LdDiagramSymbol *diagram_symbol, DrawData *data)
+{
+	LdSymbol *symbol;
+	LdRectangle clip_rect;
+	gdouble x, y;
+
+	symbol = resolve_diagram_symbol (data->self, diagram_symbol);
+
+	/* TODO: Resolve this better; draw a cross or whatever. */
+	if (!symbol)
+	{
+		g_warning ("Cannot find symbol %s in the library.",
+			ld_diagram_symbol_get_class (diagram_symbol));
+		return;
+	}
+
+	if (!get_symbol_clip_area (data->self, diagram_symbol, &clip_rect)
+		|| !ld_rectangle_intersects (&clip_rect, &data->exposed_rect))
+		return;
+
+	cairo_save (data->cr);
+
+	cairo_rectangle (data->cr, clip_rect.x, clip_rect.y,
+		clip_rect.width, clip_rect.height);
+	cairo_clip (data->cr);
+
+	/* TODO: Rotate the space for other orientations. */
+	ld_canvas_diagram_to_widget_coords (data->self,
+		ld_diagram_object_get_x (LD_DIAGRAM_OBJECT (diagram_symbol)),
+		ld_diagram_object_get_y (LD_DIAGRAM_OBJECT (diagram_symbol)),
+		&x, &y);
+	cairo_translate (data->cr, x, y);
+	cairo_scale (data->cr, data->scale, data->scale);
+	ld_symbol_draw (symbol, data->cr);
+
+	cairo_restore (data->cr);
+}
diff --git a/liblogdiag/ld-canvas.h b/liblogdiag/ld-canvas.h
new file mode 100644
index 0000000..702f2fe
--- /dev/null
+++ b/liblogdiag/ld-canvas.h
@@ -0,0 +1,91 @@
+/*
+ * ld-canvas.h
+ *
+ * This file is a part of logdiag.
+ * Copyright Přemysl Janouch 2010. All rights reserved.
+ *
+ * See the file LICENSE for licensing information.
+ *
+ */
+
+#ifndef __LD_CANVAS_H__
+#define __LD_CANVAS_H__
+
+G_BEGIN_DECLS
+
+
+#define LD_TYPE_CANVAS (ld_canvas_get_type ())
+#define LD_CANVAS(obj) (G_TYPE_CHECK_INSTANCE_CAST \
+	((obj), LD_TYPE_CANVAS, LdCanvas))
+#define LD_CANVAS_CLASS(klass) (G_TYPE_CHECK_CLASS_CAST \
+	((klass), LD_TYPE_CANVAS, LdCanvasClass))
+#define LD_IS_CANVAS(obj) (G_TYPE_CHECK_INSTANCE_TYPE \
+	((obj), LD_TYPE_CANVAS))
+#define LD_IS_CANVAS_CLASS(klass) (G_TYPE_CHECK_INSTANCE_TYPE \
+	((klass), LD_TYPE_CANVAS))
+#define LD_CANVAS_GET_CLASS(obj) (G_TYPE_INSTANCE_GET_CLASS \
+	((obj), LD_CANVAS, LdCanvasClass))
+
+typedef struct _LdCanvas LdCanvas;
+typedef struct _LdCanvasPrivate LdCanvasPrivate;
+typedef struct _LdCanvasClass LdCanvasClass;
+
+
+/**
+ * LdCanvas:
+ */
+struct _LdCanvas
+{
+/*< private >*/
+	GtkDrawingArea parent_instance;
+	LdCanvasPrivate *priv;
+
+/*< public >*/
+};
+
+struct _LdCanvasClass
+{
+/*< private >*/
+	GtkDrawingAreaClass parent_class;
+
+	guint cancel_operation_signal;
+
+	void (*set_scroll_adjustments) (LdCanvas *self,
+		GtkAdjustment *horizontal, GtkAdjustment *vertical);
+	void (*cancel_operation) (LdCanvas *self);
+};
+
+
+/**
+ * LD_CANVAS_BASE_UNIT:
+ *
+ * Length of the base unit in milimetres.
+ */
+#define LD_CANVAS_BASE_UNIT_LENGTH 2.5
+
+
+GType ld_canvas_get_type (void) G_GNUC_CONST;
+
+LdCanvas *ld_canvas_new (void);
+
+void ld_canvas_set_diagram (LdCanvas *self, LdDiagram *diagram);
+LdDiagram *ld_canvas_get_diagram (LdCanvas *self);
+void ld_canvas_set_library (LdCanvas *self, LdLibrary *library);
+LdLibrary *ld_canvas_get_library (LdCanvas *self);
+
+void ld_canvas_widget_to_diagram_coords (LdCanvas *self,
+	gdouble wx, gdouble wy, gdouble *dx, gdouble *dy);
+void ld_canvas_diagram_to_widget_coords (LdCanvas *self,
+	gdouble dx, gdouble dy, gdouble *wx, gdouble *wy);
+
+gdouble ld_canvas_get_zoom (LdCanvas *self);
+void ld_canvas_set_zoom (LdCanvas *self, gdouble zoom);
+
+void ld_canvas_add_object_begin (LdCanvas *self, LdDiagramObject *object);
+
+/* TODO: The rest of the interface. */
+
+
+G_END_DECLS
+
+#endif /* ! __LD_CANVAS_H__ */
diff --git a/liblogdiag/ld-diagram-object.c b/liblogdiag/ld-diagram-object.c
new file mode 100644
index 0000000..f43e620
--- /dev/null
+++ b/liblogdiag/ld-diagram-object.c
@@ -0,0 +1,186 @@
+/*
+ * ld-diagram-object.c
+ *
+ * This file is a part of logdiag.
+ * Copyright Přemysl Janouch 2010. All rights reserved.
+ *
+ * See the file LICENSE for licensing information.
+ *
+ */
+
+#include "liblogdiag.h"
+#include "config.h"
+
+
+/**
+ * SECTION:ld-diagram-object
+ * @short_description: A diagram object.
+ * @see_also: #LdDiagram, #LdCanvas
+ *
+ * #LdDiagramObject represents an object in an #LdDiagram.
+ */
+
+/*
+ * LdDiagramObjectPrivate:
+ * @x: The X coordinate of this object.
+ * @y: The Y coordinate of this object.
+ */
+struct _LdDiagramObjectPrivate
+{
+	gdouble x;
+	gdouble y;
+};
+
+enum
+{
+	PROP_0,
+	PROP_X,
+	PROP_Y
+};
+
+static void ld_diagram_object_get_property (GObject *object, guint property_id,
+	GValue *value, GParamSpec *pspec);
+static void ld_diagram_object_set_property (GObject *object, guint property_id,
+	const GValue *value, GParamSpec *pspec);
+
+
+G_DEFINE_ABSTRACT_TYPE (LdDiagramObject, ld_diagram_object, G_TYPE_OBJECT);
+
+static void
+ld_diagram_object_class_init (LdDiagramObjectClass *klass)
+{
+	GObjectClass *object_class;
+	GParamSpec *pspec;
+
+	object_class = G_OBJECT_CLASS (klass);
+	object_class->get_property = ld_diagram_object_get_property;
+	object_class->set_property = ld_diagram_object_set_property;
+
+/**
+ * LdDiagramObject:x:
+ *
+ * The X coordinate of the object.
+ */
+	pspec = g_param_spec_double ("x", "X",
+		"The X coordinate of this object.",
+		-G_MAXDOUBLE, G_MAXDOUBLE, 0, G_PARAM_READWRITE);
+	g_object_class_install_property (object_class, PROP_X, pspec);
+
+/**
+ * LdDiagramObject:y:
+ *
+ * The Y coordinate of the object.
+ */
+	pspec = g_param_spec_double ("y", "Y",
+		"The Y coordinate of this object.",
+		-G_MAXDOUBLE, G_MAXDOUBLE, 0, G_PARAM_READWRITE);
+	g_object_class_install_property (object_class, PROP_Y, pspec);
+
+	g_type_class_add_private (klass, sizeof (LdDiagramObjectPrivate));
+}
+
+static void
+ld_diagram_object_init (LdDiagramObject *self)
+{
+	self->priv = G_TYPE_INSTANCE_GET_PRIVATE
+		(self, LD_TYPE_DIAGRAM_OBJECT, LdDiagramObjectPrivate);
+}
+
+static void
+ld_diagram_object_get_property (GObject *object, guint property_id,
+	GValue *value, GParamSpec *pspec)
+{
+	LdDiagramObject *self;
+
+	self = LD_DIAGRAM_OBJECT (object);
+	switch (property_id)
+	{
+	case PROP_X:
+		g_value_set_double (value, ld_diagram_object_get_x (self));
+		break;
+	case PROP_Y:
+		g_value_set_double (value, ld_diagram_object_get_y (self));
+		break;
+	default:
+		G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
+	}
+}
+
+static void
+ld_diagram_object_set_property (GObject *object, guint property_id,
+	const GValue *value, GParamSpec *pspec)
+{
+	LdDiagramObject *self;
+
+	self = LD_DIAGRAM_OBJECT (object);
+	switch (property_id)
+	{
+	case PROP_X:
+		ld_diagram_object_set_x (self, g_value_get_double (value));
+		break;
+	case PROP_Y:
+		ld_diagram_object_set_y (self, g_value_get_double (value));
+		break;
+	default:
+		G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
+	}
+}
+
+
+/**
+ * ld_diagram_object_get_x:
+ * @self: An #LdDiagramObject object.
+ *
+ * Return value: The X coordinate of the object.
+ */
+gdouble
+ld_diagram_object_get_x (LdDiagramObject *self)
+{
+	g_return_val_if_fail (LD_IS_DIAGRAM_OBJECT (self), 0);
+	return self->priv->x;
+}
+
+/**
+ * ld_diagram_object_get_y:
+ * @self: An #LdDiagramObject object.
+ *
+ * Return value: The Y coordinate of the object.
+ */
+gdouble
+ld_diagram_object_get_y (LdDiagramObject *self)
+{
+	g_return_val_if_fail (LD_IS_DIAGRAM_OBJECT (self), 0);
+	return self->priv->y;
+}
+
+/**
+ * ld_diagram_object_set_x:
+ * @self: An #LdDiagramObject object.
+ * @x: The new X coordinate.
+ *
+ * Set the X coordinate of the object.
+ */
+void
+ld_diagram_object_set_x (LdDiagramObject *self, gdouble x)
+{
+	g_return_if_fail (LD_IS_DIAGRAM_OBJECT (self));
+	self->priv->x = x;
+
+	g_object_notify (G_OBJECT (self), "x");
+}
+
+/**
+ * ld_diagram_object_set_y:
+ * @self: An #LdDiagramObject object.
+ * @y: The new Y coordinate.
+ *
+ * Set the Y coordinate of the object.
+ */
+void
+ld_diagram_object_set_y (LdDiagramObject *self, gdouble y)
+{
+	g_return_if_fail (LD_IS_DIAGRAM_OBJECT (self));
+	self->priv->y = y;
+
+	g_object_notify (G_OBJECT (self), "y");
+}
diff --git a/liblogdiag/ld-diagram-object.h b/liblogdiag/ld-diagram-object.h
new file mode 100644
index 0000000..c727602
--- /dev/null
+++ b/liblogdiag/ld-diagram-object.h
@@ -0,0 +1,65 @@
+/*
+ * ld-diagram-object.h
+ *
+ * This file is a part of logdiag.
+ * Copyright Přemysl Janouch 2010. All rights reserved.
+ *
+ * See the file LICENSE for licensing information.
+ *
+ */
+
+#ifndef __LD_DIAGRAM_OBJECT_H__
+#define __LD_DIAGRAM_OBJECT_H__
+
+G_BEGIN_DECLS
+
+
+#define LD_TYPE_DIAGRAM_OBJECT (ld_diagram_object_get_type ())
+#define LD_DIAGRAM_OBJECT(obj) (G_TYPE_CHECK_INSTANCE_CAST \
+	((obj), LD_TYPE_DIAGRAM_OBJECT, LdDiagramObject))
+#define LD_DIAGRAM_OBJECT_CLASS(klass) (G_TYPE_CHECK_CLASS_CAST \
+	((klass), LD_TYPE_DIAGRAM_OBJECT, LdDiagramObjectClass))
+#define LD_IS_DIAGRAM_OBJECT(obj) (G_TYPE_CHECK_INSTANCE_TYPE \
+	((obj), LD_TYPE_DIAGRAM_OBJECT))
+#define LD_IS_DIAGRAM_OBJECT_CLASS(klass) (G_TYPE_CHECK_INSTANCE_TYPE \
+	((klass), LD_TYPE_DIAGRAM_OBJECT))
+#define LD_DIAGRAM_OBJECT_GET_CLASS(obj) (G_TYPE_INSTANCE_GET_CLASS \
+	((obj), LD_DIAGRAM_OBJECT, LdDiagramObjectClass))
+
+typedef struct _LdDiagramObject LdDiagramObject;
+typedef struct _LdDiagramObjectPrivate LdDiagramObjectPrivate;
+typedef struct _LdDiagramObjectClass LdDiagramObjectClass;
+
+
+/**
+ * LdDiagramObject:
+ */
+struct _LdDiagramObject
+{
+/*< private >*/
+	GObject parent_instance;
+	LdDiagramObjectPrivate *priv;
+};
+
+/**
+ * LdDiagramObjectClass:
+ */
+struct _LdDiagramObjectClass
+{
+/*< private >*/
+	GObjectClass parent_class;
+};
+
+
+GType ld_diagram_object_get_type (void) G_GNUC_CONST;
+
+gdouble ld_diagram_object_get_x (LdDiagramObject *self);
+gdouble ld_diagram_object_get_y (LdDiagramObject *self);
+void ld_diagram_object_set_x (LdDiagramObject *self, gdouble x);
+void ld_diagram_object_set_y (LdDiagramObject *self, gdouble y);
+
+
+G_END_DECLS
+
+#endif /* ! __LD_DIAGRAM_OBJECT_H__ */
+
diff --git a/liblogdiag/ld-diagram-symbol.c b/liblogdiag/ld-diagram-symbol.c
new file mode 100644
index 0000000..3308dbb
--- /dev/null
+++ b/liblogdiag/ld-diagram-symbol.c
@@ -0,0 +1,171 @@
+/*
+ * ld-diagram-symbol.c
+ *
+ * This file is a part of logdiag.
+ * Copyright Přemysl Janouch 2010 - 2011. All rights reserved.
+ *
+ * See the file LICENSE for licensing information.
+ *
+ */
+
+#include "liblogdiag.h"
+#include "config.h"
+
+
+/**
+ * SECTION:ld-diagram-symbol
+ * @short_description: A symbol object.
+ * @see_also: #LdDiagramObject
+ *
+ * #LdDiagramSymbol is an implementation of #LdDiagramObject.
+ */
+
+/*
+ * LdDiagramSymbolPrivate:
+ * @klass: The class of this symbol.
+ */
+struct _LdDiagramSymbolPrivate
+{
+	gchar *klass;
+};
+
+enum
+{
+	PROP_0,
+	PROP_CLASS
+};
+
+static void ld_diagram_symbol_get_property (GObject *object, guint property_id,
+	GValue *value, GParamSpec *pspec);
+static void ld_diagram_symbol_set_property (GObject *object, guint property_id,
+	const GValue *value, GParamSpec *pspec);
+static void ld_diagram_symbol_finalize (GObject *gobject);
+
+
+G_DEFINE_TYPE (LdDiagramSymbol, ld_diagram_symbol, LD_TYPE_DIAGRAM_OBJECT);
+
+static void
+ld_diagram_symbol_class_init (LdDiagramSymbolClass *klass)
+{
+	GObjectClass *object_class;
+	GParamSpec *pspec;
+
+	object_class = G_OBJECT_CLASS (klass);
+	object_class->get_property = ld_diagram_symbol_get_property;
+	object_class->set_property = ld_diagram_symbol_set_property;
+	object_class->finalize = ld_diagram_symbol_finalize;
+
+/**
+ * LdDiagramSymbol:class:
+ *
+ * The class of this symbol.
+ */
+	pspec = g_param_spec_string ("class", "Class",
+		"The class of this symbol.",
+		"", G_PARAM_READWRITE);
+	g_object_class_install_property (object_class, PROP_CLASS, pspec);
+
+	g_type_class_add_private (klass, sizeof (LdDiagramSymbolPrivate));
+}
+
+static void
+ld_diagram_symbol_init (LdDiagramSymbol *self)
+{
+	self->priv = G_TYPE_INSTANCE_GET_PRIVATE
+		(self, LD_TYPE_DIAGRAM_SYMBOL, LdDiagramSymbolPrivate);
+}
+
+static void
+ld_diagram_symbol_finalize (GObject *gobject)
+{
+	LdDiagramSymbol *self;
+
+	self = LD_DIAGRAM_SYMBOL (gobject);
+
+	if (self->priv->klass)
+		g_free (self->priv->klass);
+
+	/* Chain up to the parent class. */
+	G_OBJECT_CLASS (ld_diagram_symbol_parent_class)->finalize (gobject);
+}
+
+static void
+ld_diagram_symbol_get_property (GObject *object, guint property_id,
+	GValue *value, GParamSpec *pspec)
+{
+	LdDiagramSymbol *self;
+
+	self = LD_DIAGRAM_SYMBOL (object);
+	switch (property_id)
+	{
+	case PROP_CLASS:
+		g_value_set_string (value, ld_diagram_symbol_get_class (self));
+		break;
+	default:
+		G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
+	}
+}
+
+static void
+ld_diagram_symbol_set_property (GObject *object, guint property_id,
+	const GValue *value, GParamSpec *pspec)
+{
+	LdDiagramSymbol *self;
+
+	self = LD_DIAGRAM_SYMBOL (object);
+	switch (property_id)
+	{
+	case PROP_CLASS:
+		ld_diagram_symbol_set_class (self, g_value_get_string (value));
+		break;
+	default:
+		G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
+	}
+}
+
+
+/**
+ * ld_diagram_symbol_new:
+ * @klass: The class of the new symbol.
+ *
+ * Return value: A new #LdDiagramSymbol object.
+ */
+LdDiagramSymbol *
+ld_diagram_symbol_new (const gchar *klass)
+{
+	LdDiagramSymbol *self;
+
+	self = g_object_new (LD_TYPE_DIAGRAM_SYMBOL, NULL);
+	ld_diagram_symbol_set_class (self, klass);
+	return self;
+}
+
+/**
+ * ld_diagram_symbol_get_class:
+ * @self: An #LdDiagramSymbol object.
+ *
+ * Return value: The class of the symbol.
+ */
+const gchar *
+ld_diagram_symbol_get_class (LdDiagramSymbol *self)
+{
+	g_return_val_if_fail (LD_IS_DIAGRAM_SYMBOL (self), NULL);
+	return self->priv->klass;
+}
+
+/**
+ * ld_diagram_symbol_get_class:
+ * @self: An #LdDiagramSymbol object.
+ * @klass: The class.
+ *
+ * Set the class of the symbol.
+ */
+void
+ld_diagram_symbol_set_class (LdDiagramSymbol *self, const gchar *klass)
+{
+	g_return_if_fail (LD_IS_DIAGRAM_SYMBOL (self));
+
+	if (self->priv->klass)
+		g_free (self->priv->klass);
+	self->priv->klass = g_strdup (klass);
+}
diff --git a/liblogdiag/ld-diagram-symbol.h b/liblogdiag/ld-diagram-symbol.h
new file mode 100644
index 0000000..09d8739
--- /dev/null
+++ b/liblogdiag/ld-diagram-symbol.h
@@ -0,0 +1,64 @@
+/*
+ * ld-diagram-symbol.h
+ *
+ * This file is a part of logdiag.
+ * Copyright Přemysl Janouch 2010. All rights reserved.
+ *
+ * See the file LICENSE for licensing information.
+ *
+ */
+
+#ifndef __LD_DIAGRAM_SYMBOL_H__
+#define __LD_DIAGRAM_SYMBOL_H__
+
+G_BEGIN_DECLS
+
+
+#define LD_TYPE_DIAGRAM_SYMBOL (ld_diagram_symbol_get_type ())
+#define LD_DIAGRAM_SYMBOL(obj) (G_TYPE_CHECK_INSTANCE_CAST \
+	((obj), LD_TYPE_DIAGRAM_SYMBOL, LdDiagramSymbol))
+#define LD_DIAGRAM_SYMBOL_CLASS(klass) (G_TYPE_CHECK_CLASS_CAST \
+	((klass), LD_TYPE_DIAGRAM_SYMBOL, LdDiagramSymbolClass))
+#define LD_IS_DIAGRAM_SYMBOL(obj) (G_TYPE_CHECK_INSTANCE_TYPE \
+	((obj), LD_TYPE_DIAGRAM_SYMBOL))
+#define LD_IS_DIAGRAM_SYMBOL_CLASS(klass) (G_TYPE_CHECK_INSTANCE_TYPE \
+	((klass), LD_TYPE_DIAGRAM_SYMBOL))
+#define LD_DIAGRAM_SYMBOL_GET_CLASS(obj) (G_TYPE_INSTANCE_GET_CLASS \
+	((obj), LD_DIAGRAM_SYMBOL, LdDiagramSymbolClass))
+
+typedef struct _LdDiagramSymbol LdDiagramSymbol;
+typedef struct _LdDiagramSymbolPrivate LdDiagramSymbolPrivate;
+typedef struct _LdDiagramSymbolClass LdDiagramSymbolClass;
+
+
+/**
+ * LdDiagramSymbol:
+ */
+struct _LdDiagramSymbol
+{
+/*< private >*/
+	LdDiagramObject parent_instance;
+	LdDiagramSymbolPrivate *priv;
+};
+
+/**
+ * LdDiagramSymbolClass:
+ */
+struct _LdDiagramSymbolClass
+{
+/*< private >*/
+	LdDiagramObjectClass parent_class;
+};
+
+
+GType ld_diagram_symbol_get_type (void) G_GNUC_CONST;
+
+LdDiagramSymbol *ld_diagram_symbol_new (const gchar *klass);
+const gchar *ld_diagram_symbol_get_class (LdDiagramSymbol *self);
+void ld_diagram_symbol_set_class (LdDiagramSymbol *self, const gchar *klass);
+
+
+G_END_DECLS
+
+#endif /* ! __LD_DIAGRAM_SYMBOL_H__ */
+
diff --git a/liblogdiag/ld-diagram.c b/liblogdiag/ld-diagram.c
new file mode 100644
index 0000000..0129e2b
--- /dev/null
+++ b/liblogdiag/ld-diagram.c
@@ -0,0 +1,550 @@
+/*
+ * ld-diagram.c
+ *
+ * This file is a part of logdiag.
+ * Copyright Přemysl Janouch 2010 - 2011. All rights reserved.
+ *
+ * See the file LICENSE for licensing information.
+ *
+ */
+
+#include "liblogdiag.h"
+#include "config.h"
+
+
+/**
+ * SECTION:ld-diagram
+ * @short_description: A diagram object.
+ * @see_also: #LdCanvas
+ *
+ * #LdDiagram is a model used for storing diagrams.
+ */
+
+/*
+ * LdDiagramPrivate:
+ * @modified: Whether the diagram has been modified.
+ * @objects: All objects in the diagram.
+ * @selection: All currently selected objects.
+ * @connections: Connections between objects.
+ */
+struct _LdDiagramPrivate
+{
+	gboolean modified;
+
+	GList *objects;
+	GList *selection;
+	GList *connections;
+};
+
+enum
+{
+	PROP_0,
+	PROP_MODIFIED
+};
+
+static void ld_diagram_get_property (GObject *object, guint property_id,
+	GValue *value, GParamSpec *pspec);
+static void ld_diagram_set_property (GObject *object, guint property_id,
+	const GValue *value, GParamSpec *pspec);
+static void ld_diagram_dispose (GObject *gobject);
+static void ld_diagram_finalize (GObject *gobject);
+
+static gboolean write_signature (GOutputStream *stream, GError **error);
+
+static void ld_diagram_real_changed (LdDiagram *self);
+static void ld_diagram_clear_internal (LdDiagram *self);
+static void ld_diagram_unselect_all_internal (LdDiagram *self);
+
+
+G_DEFINE_TYPE (LdDiagram, ld_diagram, G_TYPE_OBJECT);
+
+static void
+ld_diagram_class_init (LdDiagramClass *klass)
+{
+	GObjectClass *object_class;
+	GParamSpec *pspec;
+
+	object_class = G_OBJECT_CLASS (klass);
+	object_class->get_property = ld_diagram_get_property;
+	object_class->set_property = ld_diagram_set_property;
+	object_class->dispose = ld_diagram_dispose;
+	object_class->finalize = ld_diagram_finalize;
+
+	klass->changed = ld_diagram_real_changed;
+
+/**
+ * LdDiagram:modified:
+ *
+ * Whether the diagram has been modified.
+ */
+	pspec = g_param_spec_boolean ("modified", "Modified",
+		"Whether the diagram has been modified.",
+		FALSE, G_PARAM_READWRITE);
+	g_object_class_install_property (object_class, PROP_MODIFIED, pspec);
+
+/**
+ * LdDiagram::changed:
+ * @diagram: The diagram object.
+ *
+ * Contents of the diagram have changed.
+ */
+	klass->changed_signal = g_signal_new
+		("changed", G_TYPE_FROM_CLASS (klass),
+		G_SIGNAL_RUN_LAST,
+		G_STRUCT_OFFSET (LdDiagramClass, changed), NULL, NULL,
+		g_cclosure_marshal_VOID__VOID, G_TYPE_NONE, 0);
+
+/**
+ * LdDiagram::selection-changed:
+ * @diagram: The diagram object.
+ *
+ * The current selection has changed.
+ */
+	klass->selection_changed_signal = g_signal_new
+		("selection-changed", G_TYPE_FROM_CLASS (klass),
+		G_SIGNAL_RUN_LAST,
+		G_STRUCT_OFFSET (LdDiagramClass, selection_changed), NULL, NULL,
+		g_cclosure_marshal_VOID__VOID, G_TYPE_NONE, 0);
+
+	g_type_class_add_private (klass, sizeof (LdDiagramPrivate));
+}
+
+static void
+ld_diagram_init (LdDiagram *self)
+{
+	self->priv = G_TYPE_INSTANCE_GET_PRIVATE
+		(self, LD_TYPE_DIAGRAM, LdDiagramPrivate);
+}
+
+static void
+ld_diagram_get_property (GObject *object, guint property_id,
+	GValue *value, GParamSpec *pspec)
+{
+	LdDiagram *self;
+
+	self = LD_DIAGRAM (object);
+	switch (property_id)
+	{
+	case PROP_MODIFIED:
+		g_value_set_boolean (value, ld_diagram_get_modified (self));
+		break;
+	default:
+		G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
+	}
+}
+
+static void
+ld_diagram_set_property (GObject *object, guint property_id,
+	const GValue *value, GParamSpec *pspec)
+{
+	LdDiagram *self;
+
+	self = LD_DIAGRAM (object);
+	switch (property_id)
+	{
+	case PROP_MODIFIED:
+		ld_diagram_set_modified (self, g_value_get_boolean (value));
+		break;
+	default:
+		G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
+	}
+}
+
+static void
+ld_diagram_dispose (GObject *gobject)
+{
+	LdDiagram *self;
+
+	self = LD_DIAGRAM (gobject);
+	ld_diagram_clear_internal (self);
+
+	/* Chain up to the parent class. */
+	G_OBJECT_CLASS (ld_diagram_parent_class)->dispose (gobject);
+}
+
+static void
+ld_diagram_finalize (GObject *gobject)
+{
+	/* Chain up to the parent class. */
+	G_OBJECT_CLASS (ld_diagram_parent_class)->finalize (gobject);
+}
+
+static void
+ld_diagram_real_changed (LdDiagram *self)
+{
+	g_return_if_fail (LD_IS_DIAGRAM (self));
+
+	ld_diagram_set_modified (self, TRUE);
+}
+
+
+/**
+ * ld_diagram_new:
+ *
+ * Create an instance.
+ */
+LdDiagram *
+ld_diagram_new (void)
+{
+	return g_object_new (LD_TYPE_DIAGRAM, NULL);
+}
+
+/**
+ * ld_diagram_clear:
+ * @self: An #LdDiagram object.
+ *
+ * Clear the whole diagram with it's objects and selection.
+ */
+void
+ld_diagram_clear (LdDiagram *self)
+{
+	g_return_if_fail (LD_IS_DIAGRAM (self));
+
+	ld_diagram_clear_internal (self);
+
+	g_signal_emit (self,
+		LD_DIAGRAM_GET_CLASS (self)->changed_signal, 0);
+}
+
+/*
+ * ld_diagram_clear_internal:
+ * @self: An #LdDiagram object.
+ *
+ * Do the same as ld_diagram_clear() does but don't emit signals.
+ */
+static void
+ld_diagram_clear_internal (LdDiagram *self)
+{
+	ld_diagram_unselect_all (self);
+
+	g_list_free (self->priv->connections);
+	self->priv->connections = NULL;
+
+	g_list_foreach (self->priv->objects, (GFunc) g_object_unref, NULL);
+	g_list_free (self->priv->objects);
+	self->priv->objects = NULL;
+}
+
+/**
+ * ld_diagram_load_from_file:
+ * @self: An #LdDiagram object.
+ * @filename: A filename.
+ * @error: Return location for a GError, or NULL.
+ *
+ * Load a file into the diagram.
+ *
+ * Return value: TRUE if the file could be loaded, FALSE otherwise.
+ */
+gboolean
+ld_diagram_load_from_file (LdDiagram *self,
+	const gchar *filename, GError **error)
+{
+	JsonParser *parser;
+	GError *json_error;
+
+	g_return_val_if_fail (LD_IS_DIAGRAM (self), FALSE);
+	g_return_val_if_fail (filename != NULL, FALSE);
+
+	/* TODO: Implement loading for real. This is just a stub. */
+	parser = json_parser_new ();
+
+	json_error = NULL;
+	json_parser_load_from_file (parser, filename, &json_error);
+	if (json_error)
+	{
+		g_propagate_error (error, json_error);
+		g_object_unref (parser);
+		return FALSE;
+	}
+
+	ld_diagram_clear (self);
+	g_object_unref (parser);
+	return TRUE;
+}
+
+/**
+ * ld_diagram_save_to_file:
+ * @self: An #LdDiagram object.
+ * @filename: A filename.
+ * @error: Return location for a GError, or NULL.
+ *
+ * Save the diagram into a file.
+ *
+ * Return value: TRUE if the diagram could be saved, FALSE otherwise.
+ */
+gboolean
+ld_diagram_save_to_file (LdDiagram *self,
+	const gchar *filename, GError **error)
+{
+	GFile *file;
+	GFileOutputStream *file_stream;
+	JsonGenerator *generator;
+	JsonNode *root;
+	GError *local_error;
+
+	g_return_val_if_fail (LD_IS_DIAGRAM (self), FALSE);
+	g_return_val_if_fail (filename != NULL, FALSE);
+
+	file = g_file_new_for_path (filename);
+
+	local_error = NULL;
+	file_stream = g_file_replace (file, NULL, FALSE,
+		G_FILE_CREATE_NONE, NULL, &local_error);
+	g_object_unref (file);
+
+	if (local_error)
+	{
+		g_propagate_error (error, local_error);
+		return FALSE;
+	}
+
+	local_error = NULL;
+	write_signature (G_OUTPUT_STREAM (file_stream), &local_error);
+	if (local_error)
+	{
+		g_object_unref (file_stream);
+		g_propagate_error (error, local_error);
+		return FALSE;
+	}
+
+	/* TODO: Implement saving for real. This is just a stub. */
+	generator = json_generator_new ();
+	g_object_set (generator, "pretty", TRUE, NULL);
+
+	/* XXX: json-glib dislikes empty objects. */
+	root = json_node_new (JSON_NODE_OBJECT);
+	json_generator_set_root (generator, root);
+	json_node_free (root);
+
+	local_error = NULL;
+	json_generator_to_stream (generator, G_OUTPUT_STREAM (file_stream),
+		NULL, &local_error);
+	g_object_unref (file_stream);
+	g_object_unref (generator);
+
+	if (local_error)
+	{
+		g_propagate_error (error, local_error);
+		return FALSE;
+	}
+	return TRUE;
+}
+
+static gboolean
+write_signature (GOutputStream *stream, GError **error)
+{
+	static const gchar signature[] = "/* logdiag diagram */\n";
+	GError *local_error = NULL;
+
+	g_output_stream_write (stream, signature, sizeof (signature) - 1,
+		NULL, &local_error);
+	if (local_error)
+	{
+		g_propagate_error (error, local_error);
+		return FALSE;
+	}
+	return TRUE;
+}
+
+/**
+ * ld_diagram_get_modified:
+ * @self: An #LdDiagram object.
+ *
+ * Return value: The modification status of diagram.
+ */
+gboolean
+ld_diagram_get_modified (LdDiagram *self)
+{
+	g_return_val_if_fail (LD_IS_DIAGRAM (self), FALSE);
+	return self->priv->modified;
+}
+
+/**
+ * ld_diagram_set_modified:
+ * @self: An #LdDiagram object.
+ * @value: Whether the diagram has been modified.
+ *
+ * Set the modification status of diagram.
+ */
+void
+ld_diagram_set_modified (LdDiagram *self, gboolean value)
+{
+	g_return_if_fail (LD_IS_DIAGRAM (self));
+	self->priv->modified = value;
+
+	g_object_notify (G_OBJECT (self), "modified");
+}
+
+/**
+ * ld_diagram_get_objects:
+ * @self: An #LdDiagram object.
+ *
+ * Get a list of objects in the diagram. Do not modify.
+ */
+GList *
+ld_diagram_get_objects (LdDiagram *self)
+{
+	g_return_val_if_fail (LD_IS_DIAGRAM (self), NULL);
+	return self->priv->objects;
+}
+
+/**
+ * ld_diagram_insert_object:
+ * @self: An #LdDiagram object.
+ * @object: The object to be inserted.
+ * @pos: The position at which the object is to be inserted.
+ *       Negative values will append to the end.
+ *
+ * Insert an object into the diagram.
+ */
+void
+ld_diagram_insert_object (LdDiagram *self, LdDiagramObject *object, gint pos)
+{
+	g_return_if_fail (LD_IS_DIAGRAM (self));
+	g_return_if_fail (LD_IS_DIAGRAM_OBJECT (object));
+
+	if (!g_list_find (self->priv->objects, object))
+	{
+		self->priv->objects =
+			g_list_insert (self->priv->objects, object, pos);
+		g_object_ref (object);
+
+		g_signal_emit (self,
+			LD_DIAGRAM_GET_CLASS (self)->changed_signal, 0);
+	}
+}
+
+/**
+ * ld_diagram_remove_object:
+ * @self: An #LdDiagram object.
+ * @object: The object to be removed.
+ *
+ * Remove an object from the diagram.
+ */
+void
+ld_diagram_remove_object (LdDiagram *self, LdDiagramObject *object)
+{
+	g_return_if_fail (LD_IS_DIAGRAM (self));
+	g_return_if_fail (LD_IS_DIAGRAM_OBJECT (object));
+
+	if (g_list_find (self->priv->objects, object))
+	{
+		ld_diagram_selection_remove (self, object);
+
+		self->priv->objects = g_list_remove (self->priv->objects, object);
+		g_object_unref (object);
+
+		g_signal_emit (self,
+			LD_DIAGRAM_GET_CLASS (self)->changed_signal, 0);
+	}
+}
+
+/**
+ * ld_diagram_get_selection:
+ * @self: An #LdDiagram object.
+ *
+ * Get a list of objects that are currently selected in the diagram.
+ * Do not modify.
+ */
+GList *
+ld_diagram_get_selection (LdDiagram *self)
+{
+	g_return_val_if_fail (LD_IS_DIAGRAM (self), NULL);
+	return self->priv->selection;
+}
+
+/**
+ * ld_diagram_selection_add:
+ * @self: An #LdDiagram object.
+ * @object: The object to be added to the selection.
+ * @pos: The position at which the object is to be inserted.
+ *       Negative values will append to the end.
+ *
+ * Add an object to selection.
+ */
+void
+ld_diagram_selection_add (LdDiagram *self, LdDiagramObject *object, gint pos)
+{
+	g_return_if_fail (LD_IS_DIAGRAM (self));
+	g_return_if_fail (LD_IS_DIAGRAM_OBJECT (object));
+
+	g_return_if_fail (g_list_find (self->priv->objects, object) != NULL);
+
+	if (!g_list_find (self->priv->selection, object))
+	{
+		self->priv->selection =
+			g_list_insert (self->priv->selection, object, pos);
+		g_object_ref (object);
+
+		g_signal_emit (self,
+			LD_DIAGRAM_GET_CLASS (self)->selection_changed_signal, 0);
+	}
+}
+
+/**
+ * ld_diagram_selection_remove:
+ * @self: An #LdDiagram object.
+ * @object: The object to be removed from the selection.
+ *
+ * Remove an object from the selection.
+ */
+void
+ld_diagram_selection_remove (LdDiagram *self, LdDiagramObject *object)
+{
+	g_return_if_fail (LD_IS_DIAGRAM (self));
+	g_return_if_fail (LD_IS_DIAGRAM_OBJECT (object));
+
+	if (g_list_find (self->priv->selection, object))
+	{
+		self->priv->selection = g_list_remove (self->priv->selection, object);
+		g_object_unref (object);
+
+		g_signal_emit (self,
+			LD_DIAGRAM_GET_CLASS (self)->selection_changed_signal, 0);
+	}
+}
+
+/**
+ * ld_diagram_select_all:
+ * @self: An #LdDiagram object.
+ *
+ * Include all objects in the document to the selection.
+ */
+void
+ld_diagram_select_all (LdDiagram *self)
+{
+	g_return_if_fail (LD_IS_DIAGRAM (self));
+
+	ld_diagram_unselect_all_internal (self);
+
+	self->priv->selection = g_list_copy (self->priv->objects);
+	g_list_foreach (self->priv->selection, (GFunc) g_object_ref, NULL);
+
+	g_signal_emit (self,
+		LD_DIAGRAM_GET_CLASS (self)->selection_changed_signal, 0);
+}
+
+/**
+ * ld_diagram_unselect_all:
+ * @self: An #LdDiagram object.
+ *
+ * Remove all objects from the current selection.
+ */
+void
+ld_diagram_unselect_all (LdDiagram *self)
+{
+	g_return_if_fail (LD_IS_DIAGRAM (self));
+
+	ld_diagram_unselect_all_internal (self);
+
+	g_signal_emit (self,
+		LD_DIAGRAM_GET_CLASS (self)->selection_changed_signal, 0);
+}
+
+static void
+ld_diagram_unselect_all_internal (LdDiagram *self)
+{
+	g_list_foreach (self->priv->selection, (GFunc) g_object_unref, NULL);
+	g_list_free (self->priv->selection);
+	self->priv->selection = NULL;
+}
diff --git a/liblogdiag/ld-diagram.h b/liblogdiag/ld-diagram.h
new file mode 100644
index 0000000..f364189
--- /dev/null
+++ b/liblogdiag/ld-diagram.h
@@ -0,0 +1,98 @@
+/*
+ * ld-diagram.h
+ *
+ * This file is a part of logdiag.
+ * Copyright Přemysl Janouch 2010 - 2011. All rights reserved.
+ *
+ * See the file LICENSE for licensing information.
+ *
+ */
+
+#ifndef __LD_DIAGRAM_H__
+#define __LD_DIAGRAM_H__
+
+G_BEGIN_DECLS
+
+
+#define LD_TYPE_DIAGRAM (ld_diagram_get_type ())
+#define LD_DIAGRAM(obj) (G_TYPE_CHECK_INSTANCE_CAST \
+	((obj), LD_TYPE_DIAGRAM, LdDiagram))
+#define LD_DIAGRAM_CLASS(klass) (G_TYPE_CHECK_CLASS_CAST \
+	((klass), LD_TYPE_DIAGRAM, LdDiagramClass))
+#define LD_IS_DIAGRAM(obj) (G_TYPE_CHECK_INSTANCE_TYPE \
+	((obj), LD_TYPE_DIAGRAM))
+#define LD_IS_DIAGRAM_CLASS(klass) (G_TYPE_CHECK_INSTANCE_TYPE \
+	((klass), LD_TYPE_DIAGRAM))
+#define LD_DIAGRAM_GET_CLASS(obj) (G_TYPE_INSTANCE_GET_CLASS \
+	((obj), LD_DIAGRAM, LdDiagramClass))
+
+typedef struct _LdDiagram LdDiagram;
+typedef struct _LdDiagramClass LdDiagramClass;
+typedef struct _LdDiagramPrivate LdDiagramPrivate;
+
+
+/**
+ * LdDiagram:
+ *
+ * A diagram object.
+ */
+struct _LdDiagram
+{
+/*< private >*/
+	GObject parent_instance;
+	LdDiagramPrivate *priv;
+};
+
+struct _LdDiagramClass
+{
+/*< private >*/
+	GObjectClass parent_class;
+
+	guint changed_signal;
+	guint selection_changed_signal;
+
+	void (*changed) (LdDiagram *self);
+	void (*selection_changed) (LdDiagram *self);
+};
+
+
+GType ld_diagram_get_type (void) G_GNUC_CONST;
+
+LdDiagram *ld_diagram_new (void);
+void ld_diagram_clear (LdDiagram *self);
+gboolean ld_diagram_load_from_file (LdDiagram *self,
+	const gchar *filename, GError **error);
+gboolean ld_diagram_save_to_file (LdDiagram *self,
+	const gchar *filename, GError **error);
+
+gboolean ld_diagram_get_modified (LdDiagram *self);
+void ld_diagram_set_modified (LdDiagram *self, gboolean value);
+
+GList *ld_diagram_get_objects (LdDiagram *self);
+void ld_diagram_insert_object (LdDiagram *self,
+	LdDiagramObject *object, gint pos);
+void ld_diagram_remove_object (LdDiagram *self,
+	LdDiagramObject *object);
+
+GList *ld_diagram_get_selection (LdDiagram *self);
+void ld_diagram_selection_add (LdDiagram *self,
+	LdDiagramObject *object, gint pos);
+void ld_diagram_selection_remove (LdDiagram *self,
+	LdDiagramObject *object);
+
+void ld_diagram_select_all (LdDiagram *self);
+void ld_diagram_unselect_all (LdDiagram *self);
+
+/*
+GList *ld_diagram_get_connections (LdDiagram *self);
+void ld_diagram_connection_add (LdDiagram *self,
+	LdConnection *connection, gint pos);
+void ld_diagram_connection_remove (LdDiagram *self,
+	LdConnection *connection);
+*/
+
+
+G_END_DECLS
+
+#endif /* ! __LD_DIAGRAM_H__ */
+
diff --git a/liblogdiag/ld-library.c b/liblogdiag/ld-library.c
new file mode 100644
index 0000000..37e2bc9
--- /dev/null
+++ b/liblogdiag/ld-library.c
@@ -0,0 +1,524 @@
+/*
+ * ld-library.c
+ *
+ * This file is a part of logdiag.
+ * Copyright Přemysl Janouch 2010 - 2011. All rights reserved.
+ *
+ * See the file LICENSE for licensing information.
+ *
+ */
+
+#include <string.h>
+
+#include "liblogdiag.h"
+#include "config.h"
+
+
+/**
+ * SECTION:ld-library
+ * @short_description: A symbol library.
+ * @see_also: #LdSymbol, #LdSymbolCategory
+ *
+ * #LdLibrary is used for loading symbols from their files.
+ */
+
+/*
+ * LdLibraryPrivate:
+ * @lua: State of the scripting language.
+ * @children: Child objects of the library.
+ */
+struct _LdLibraryPrivate
+{
+	LdLua *lua;
+	GSList *children;
+};
+
+static void ld_library_finalize (GObject *gobject);
+
+static LdSymbolCategory *load_category (LdLibrary *self,
+	const gchar *path, const gchar *name);
+static gboolean load_category_cb (const gchar *base,
+	const gchar *filename, gpointer userdata);
+static void load_category_symbol_cb (LdSymbol *symbol, gpointer user_data);
+
+static gchar *read_human_name_from_file (const gchar *filename);
+
+static gboolean foreach_dir (const gchar *path,
+	gboolean (*callback) (const gchar *, const gchar *, gpointer),
+	gpointer userdata, GError **error);
+static gboolean ld_library_load_cb
+	(const gchar *base, const gchar *filename, gpointer userdata);
+
+
+G_DEFINE_TYPE (LdLibrary, ld_library, G_TYPE_OBJECT);
+
+static void
+ld_library_class_init (LdLibraryClass *klass)
+{
+	GObjectClass *object_class;
+
+	object_class = G_OBJECT_CLASS (klass);
+	object_class->finalize = ld_library_finalize;
+
+/**
+ * LdLibrary::changed:
+ * @library: The library object.
+ *
+ * Contents of the library have changed.
+ */
+	klass->changed_signal = g_signal_new
+		("changed", G_TYPE_FROM_CLASS (klass),
+		G_SIGNAL_RUN_LAST, 0, NULL, NULL,
+		g_cclosure_marshal_VOID__VOID, G_TYPE_NONE, 0);
+
+	g_type_class_add_private (klass, sizeof (LdLibraryPrivate));
+}
+
+static void
+ld_library_init (LdLibrary *self)
+{
+	self->priv = G_TYPE_INSTANCE_GET_PRIVATE
+		(self, LD_TYPE_LIBRARY, LdLibraryPrivate);
+
+	self->priv->lua = ld_lua_new ();
+	self->priv->children = NULL;
+}
+
+static void
+ld_library_finalize (GObject *gobject)
+{
+	LdLibrary *self;
+
+	self = LD_LIBRARY (gobject);
+
+	g_object_unref (self->priv->lua);
+
+	g_slist_foreach (self->priv->children, (GFunc) g_object_unref, NULL);
+	g_slist_free (self->priv->children);
+
+	/* Chain up to the parent class. */
+	G_OBJECT_CLASS (ld_library_parent_class)->finalize (gobject);
+}
+
+/**
+ * ld_library_new:
+ *
+ * Create an instance.
+ */
+LdLibrary *
+ld_library_new (void)
+{
+	return g_object_new (LD_TYPE_LIBRARY, NULL);
+}
+
+/*
+ * foreach_dir:
+ *
+ * Call a user-defined function for each file within a directory.
+ */
+static gboolean
+foreach_dir (const gchar *path,
+	gboolean (*callback) (const gchar *, const gchar *, gpointer),
+	gpointer userdata, GError **error)
+{
+	GDir *dir;
+	const gchar *item;
+
+	g_return_val_if_fail (path != NULL, FALSE);
+	g_return_val_if_fail (callback != NULL, FALSE);
+
+	dir = g_dir_open (path, 0, error);
+	if (!dir)
+		return FALSE;
+
+	while ((item = g_dir_read_name (dir)))
+	{
+		gchar *filename;
+
+		filename = g_build_filename (path, item, NULL);
+		if (!callback (item, filename, userdata))
+			break;
+		g_free (filename);
+	}
+	g_dir_close (dir);
+	return TRUE;
+}
+
+/*
+ * LoadCategoryData:
+ *
+ * Data shared between load_category() and load_category_cb().
+ */
+typedef struct
+{
+	LdLibrary *self;
+	LdSymbolCategory *cat;
+}
+LoadCategoryData;
+
+/*
+ * load_category:
+ * @self: An #LdLibrary object.
+ * @path: The path to the category.
+ * @name: The default name of the category.
+ *
+ * Loads a category into the library.
+ */
+static LdSymbolCategory *
+load_category (LdLibrary *self, const gchar *path, const gchar *name)
+{
+	LdSymbolCategory *cat;
+	gchar *icon_file, *category_file;
+	gchar *human_name;
+	LoadCategoryData data;
+
+	g_return_val_if_fail (LD_IS_LIBRARY (self), NULL);
+	g_return_val_if_fail (path != NULL, NULL);
+	g_return_val_if_fail (name != NULL, NULL);
+
+	if (!g_file_test (path, G_FILE_TEST_IS_DIR))
+		goto load_category_fail_1;
+
+	icon_file = g_build_filename (path, "icon.svg", NULL);
+	if (!g_file_test (icon_file, G_FILE_TEST_IS_REGULAR))
+	{
+		g_warning ("The category in %s has no icon.", path);
+		goto load_category_fail_2;
+	}
+
+	category_file = g_build_filename (path, "category.json", NULL);
+	human_name = read_human_name_from_file (category_file);
+	if (!human_name)
+		human_name = g_strdup (name);
+
+	cat = ld_symbol_category_new (name, human_name);
+	ld_symbol_category_set_image_path (cat, icon_file);
+
+	data.self = self;
+	data.cat = cat;
+	foreach_dir (path, load_category_cb, &data, NULL);
+
+	g_free (human_name);
+	g_free (category_file);
+	g_free (icon_file);
+	return cat;
+
+load_category_fail_2:
+	g_free (icon_file);
+load_category_fail_1:
+	return NULL;
+}
+
+/*
+ * load_category_cb:
+ *
+ * Load script files from a directory into a symbol category.
+ */
+static gboolean
+load_category_cb (const gchar *base, const gchar *filename, gpointer userdata)
+{
+	LoadCategoryData *data;
+
+	g_return_val_if_fail (base != NULL, FALSE);
+	g_return_val_if_fail (filename != NULL, FALSE);
+	g_return_val_if_fail (userdata != NULL, FALSE);
+
+	data = (LoadCategoryData *) userdata;
+
+	if (ld_lua_check_file (data->self->priv->lua, filename))
+		ld_lua_load_file (data->self->priv->lua, filename,
+			load_category_symbol_cb, data->cat);
+	return TRUE;
+}
+
+/*
+ * load_category_symbol_cb:
+ *
+ * Insert newly registered symbols into the category.
+ */
+static void
+load_category_symbol_cb (LdSymbol *symbol, gpointer user_data)
+{
+	const gchar *name;
+	LdSymbolCategory *cat;
+	const GSList *children, *iter;
+
+	g_return_if_fail (LD_IS_SYMBOL (symbol));
+	g_return_if_fail (LD_IS_SYMBOL_CATEGORY (user_data));
+
+	cat = LD_SYMBOL_CATEGORY (user_data);
+	name = ld_symbol_get_name (symbol);
+
+	/* Check for name collisions with other symbols. */
+	children = ld_symbol_category_get_children (cat);
+	for (iter = children; iter; iter = iter->next)
+	{
+		if (!LD_IS_SYMBOL (iter->data))
+			continue;
+		if (!strcmp (name, ld_symbol_get_name (LD_SYMBOL (iter->data))))
+		{
+			g_warning ("Attempted to insert multiple '%s' symbols into"
+				" category '%s'.", name, ld_symbol_category_get_name (cat));
+			return;
+		}
+	}
+	ld_symbol_category_insert_child (cat, G_OBJECT (symbol), -1);
+}
+
+/*
+ * read_human_name_from_file:
+ * @filename: Location of the JSON file.
+ *
+ * Read the human name of the processed category.
+ */
+static gchar *
+read_human_name_from_file (const gchar *filename)
+{
+	const gchar *const *lang;
+	JsonParser *parser;
+	JsonNode *root;
+	JsonObject *object;
+	GError *error;
+
+	g_return_val_if_fail (filename != NULL, NULL);
+
+	parser = json_parser_new ();
+	error = NULL;
+	if (!json_parser_load_from_file (parser, filename, &error))
+	{
+		g_warning ("%s", error->message);
+		g_error_free (error);
+		goto read_human_name_from_file_end;
+	}
+
+	root = json_parser_get_root (parser);
+	if (!JSON_NODE_HOLDS_OBJECT (root))
+	{
+		g_warning ("Failed to parse '%s': %s", filename,
+			"The root node is not an object.");
+		goto read_human_name_from_file_end;
+	}
+
+	object = json_node_get_object (root);
+	for (lang = g_get_language_names (); *lang; lang++)
+	{
+		const gchar *member;
+
+		if (!json_object_has_member (object, *lang))
+			continue;
+		member = json_object_get_string_member (object, *lang);
+
+		if (member != NULL)
+		{
+			gchar *result;
+
+			result = g_strdup (member);
+			g_object_unref (parser);
+			return result;
+		}
+	}
+
+read_human_name_from_file_end:
+	g_object_unref (parser);
+	return NULL;
+}
+
+/*
+ * LibraryLoadData:
+ *
+ * Data shared between ld_library_load() and ld_library_load_cb().
+ */
+typedef struct
+{
+	LdLibrary *self;
+	gboolean changed;
+}
+LibraryLoadData;
+
+/**
+ * ld_library_load:
+ * @self: An #LdLibrary object.
+ * @directory: A directory to be loaded.
+ *
+ * Load the contents of a directory into the library.
+ */
+gboolean
+ld_library_load (LdLibrary *self, const gchar *directory)
+{
+	LibraryLoadData data;
+
+	g_return_val_if_fail (LD_IS_LIBRARY (self), FALSE);
+	g_return_val_if_fail (directory != NULL, FALSE);
+
+	data.self = self;
+	data.changed = FALSE;
+	foreach_dir (directory, ld_library_load_cb, &data, NULL);
+
+	if (data.changed)
+		g_signal_emit (self, LD_LIBRARY_GET_CLASS (self)->changed_signal, 0);
+
+	return TRUE;
+}
+
+/*
+ * ld_library_load_cb:
+ *
+ * A callback that's called for each file in the root directory.
+ */
+static gboolean
+ld_library_load_cb (const gchar *base, const gchar *filename, gpointer userdata)
+{
+	LdSymbolCategory *cat;
+	LibraryLoadData *data;
+
+	g_return_val_if_fail (base != NULL, FALSE);
+	g_return_val_if_fail (filename != NULL, FALSE);
+	g_return_val_if_fail (userdata != NULL, FALSE);
+
+	data = (LibraryLoadData *) userdata;
+
+	cat = load_category (data->self, filename, base);
+	if (cat)
+		ld_library_insert_child (data->self, G_OBJECT (cat), -1);
+
+	data->changed = TRUE;
+	return TRUE;
+}
+
+/**
+ * ld_library_find_symbol:
+ * @self: An #LdLibrary object.
+ * @identifier: An identifier of the symbol to be searched for.
+ *
+ * Search for a symbol in the library.
+ *
+ * Return value: A symbol object if found, NULL otherwise.
+ */
+/* XXX: With this level of indentation, this function is really ugly. */
+LdSymbol *
+ld_library_find_symbol (LdLibrary *self, const gchar *identifier)
+{
+	gchar **id_el_start, **id_el;
+	const GSList *list, *list_el;
+
+	g_return_val_if_fail (LD_IS_LIBRARY (self), NULL);
+	g_return_val_if_fail (identifier != NULL, NULL);
+
+	id_el_start = g_strsplit (identifier, LD_LIBRARY_IDENTIFIER_SEPARATOR, 0);
+	if (!id_el_start)
+		return NULL;
+
+	list = ld_library_get_children (self);
+	for (id_el = id_el_start; id_el[0]; id_el++)
+	{
+		LdSymbolCategory *cat;
+		LdSymbol *symbol;
+		gboolean found = FALSE;
+
+		for (list_el = list; list_el; list_el = g_slist_next (list_el))
+		{
+			/* If the current identifier element is a category (not last)
+			 * and this list element is a category.
+			 */
+			if (id_el[1] && LD_IS_SYMBOL_CATEGORY (list_el->data))
+			{
+				cat = LD_SYMBOL_CATEGORY (list_el->data);
+				if (strcmp (id_el[0], ld_symbol_category_get_name (cat)))
+					continue;
+
+				list = ld_symbol_category_get_children (cat);
+				found = TRUE;
+				break;
+			}
+			/* If the current identifier element is a symbol (last)
+			 * and this list element is a symbol.
+			 */
+			else if (!id_el[1] && LD_IS_SYMBOL (list_el->data))
+			{
+				symbol = LD_SYMBOL (list_el->data);
+				if (strcmp (id_el[0], ld_symbol_get_name (symbol)))
+					continue;
+
+				g_strfreev (id_el_start);
+				return symbol;
+			}
+		}
+
+		if (!found)
+			break;
+	}
+	g_strfreev (id_el_start);
+	return NULL;
+}
+
+/**
+ * ld_library_clear:
+ * @self: An #LdLibrary object.
+ *
+ * Clear all the contents.
+ */
+void
+ld_library_clear (LdLibrary *self)
+{
+	g_return_if_fail (LD_IS_LIBRARY (self));
+
+	g_slist_foreach (self->priv->children, (GFunc) g_object_unref, NULL);
+	g_slist_free (self->priv->children);
+	self->priv->children = NULL;
+
+	g_signal_emit (self,
+		LD_LIBRARY_GET_CLASS (self)->changed_signal, 0);
+}
+
+/**
+ * ld_library_insert_child:
+ * @self: An #LdLibrary object.
+ * @child: The child to be inserted.
+ * @pos: The position at which the child will be inserted.
+ *       Negative values will append to the end of list.
+ *
+ * Insert a child into the library.
+ */
+void
+ld_library_insert_child (LdLibrary *self, GObject *child, gint pos)
+{
+	g_return_if_fail (LD_IS_LIBRARY (self));
+	g_return_if_fail (G_IS_OBJECT (child));
+
+	g_object_ref (child);
+	self->priv->children = g_slist_insert (self->priv->children, child, pos);
+}
+
+/**
+ * ld_library_remove_child:
+ * @self: An #LdLibrary object.
+ * @child: The child to be removed.
+ *
+ * Remove a child from the library.
+ */
+void
+ld_library_remove_child (LdLibrary *self, GObject *child)
+{
+	g_return_if_fail (LD_IS_LIBRARY (self));
+	g_return_if_fail (G_IS_OBJECT (child));
+
+	if (g_slist_find (self->priv->children, child))
+	{
+		g_object_unref (child);
+		self->priv->children = g_slist_remove (self->priv->children, child);
+	}
+}
+
+/**
+ * ld_library_get_children:
+ * @self: An #LdLibrary object.
+ *
+ * Return value: The internal list of children. Do not modify.
+ */
+const GSList *
+ld_library_get_children (LdLibrary *self)
+{
+	g_return_val_if_fail (LD_IS_LIBRARY (self), NULL);
+	return self->priv->children;
+}
+
diff --git a/liblogdiag/ld-library.h b/liblogdiag/ld-library.h
new file mode 100644
index 0000000..26521ed
--- /dev/null
+++ b/liblogdiag/ld-library.h
@@ -0,0 +1,73 @@
+/*
+ * ld-library.h
+ *
+ * This file is a part of logdiag.
+ * Copyright Přemysl Janouch 2010. All rights reserved.
+ *
+ * See the file LICENSE for licensing information.
+ *
+ */
+
+#ifndef __LD_LIBRARY_H__
+#define __LD_LIBRARY_H__
+
+G_BEGIN_DECLS
+
+
+#define LD_TYPE_LIBRARY (ld_library_get_type ())
+#define LD_LIBRARY(obj) (G_TYPE_CHECK_INSTANCE_CAST \
+	((obj), LD_TYPE_LIBRARY, LdLibrary))
+#define LD_LIBRARY_CLASS(klass) (G_TYPE_CHECK_CLASS_CAST \
+	((klass), LD_TYPE_LIBRARY, LdLibraryClass))
+#define LD_IS_LIBRARY(obj) (G_TYPE_CHECK_INSTANCE_TYPE \
+	((obj), LD_TYPE_LIBRARY))
+#define LD_IS_LIBRARY_CLASS(klass) (G_TYPE_CHECK_INSTANCE_TYPE \
+	((klass), LD_TYPE_LIBRARY))
+#define LD_LIBRARY_GET_CLASS(obj) (G_TYPE_INSTANCE_GET_CLASS \
+	((obj), LD_LIBRARY, LdLibraryClass))
+
+typedef struct _LdLibrary LdLibrary;
+typedef struct _LdLibraryPrivate LdLibraryPrivate;
+typedef struct _LdLibraryClass LdLibraryClass;
+
+
+struct _LdLibrary
+{
+/*< private >*/
+	GObject parent_instance;
+	LdLibraryPrivate *priv;
+};
+
+struct _LdLibraryClass
+{
+/*< private >*/
+	GObjectClass parent_class;
+
+	guint changed_signal;
+};
+
+
+/**
+ * LD_LIBRARY_IDENTIFIER_SEPARATOR:
+ *
+ * Defines a string that separates categories and symbols in identifiers.
+ */
+#define LD_LIBRARY_IDENTIFIER_SEPARATOR "/"
+
+
+GType ld_library_get_type (void) G_GNUC_CONST;
+
+LdLibrary *ld_library_new (void);
+gboolean ld_library_load (LdLibrary *self, const gchar *directory);
+LdSymbol *ld_library_find_symbol (LdLibrary *self, const gchar *identifier);
+void ld_library_clear (LdLibrary *self);
+
+void ld_library_insert_child (LdLibrary *self, GObject *child, gint pos);
+void ld_library_remove_child (LdLibrary *self, GObject *child);
+const GSList *ld_library_get_children (LdLibrary *self);
+
+
+G_END_DECLS
+
+#endif /* ! __LD_LIBRARY_H__ */
+
diff --git a/liblogdiag/ld-lua-private.h b/liblogdiag/ld-lua-private.h
new file mode 100644
index 0000000..7d6943a
--- /dev/null
+++ b/liblogdiag/ld-lua-private.h
@@ -0,0 +1,26 @@
+/*
+ * ld-lua-private.h
+ *
+ * This file is a part of logdiag.
+ * Copyright Přemysl Janouch 2010. All rights reserved.
+ *
+ * See the file LICENSE for licensing information.
+ *
+ */
+
+#ifndef __LD_LUA_PRIVATE_H__
+#define __LD_LUA_PRIVATE_H__
+
+G_BEGIN_DECLS
+
+
+/*< private_header >*/
+
+void ld_lua_private_unregister (LdLua *self, LdLuaSymbol *symbol);
+void ld_lua_private_draw (LdLua *self, LdLuaSymbol *symbol, cairo_t *cr);
+
+
+G_END_DECLS
+
+#endif /* ! __LD_LUA_PRIVATE_H__ */
+
diff --git a/liblogdiag/ld-lua-symbol-private.h b/liblogdiag/ld-lua-symbol-private.h
new file mode 100644
index 0000000..83bc646
--- /dev/null
+++ b/liblogdiag/ld-lua-symbol-private.h
@@ -0,0 +1,40 @@
+/*
+ * ld-lua-symbol-private.h
+ *
+ * This file is a part of logdiag.
+ * Copyright Přemysl Janouch 2010 - 2011. All rights reserved.
+ *
+ * See the file LICENSE for licensing information.
+ *
+ */
+
+#ifndef __LD_LUA_SYMBOL_PRIVATE_H__
+#define __LD_LUA_SYMBOL_PRIVATE_H__
+
+G_BEGIN_DECLS
+
+
+/*< private_header >*/
+
+/*
+ * LdLuaSymbolPrivate:
+ * @lua: Parent #LdLua object.
+ * @name: Name of this symbol.
+ * @human_name: Localized human name of this symbol.
+ * @area: Area of this symbol.
+ * @terminals: Terminals of this symbol.
+ */
+struct _LdLuaSymbolPrivate
+{
+	LdLua *lua;
+	gchar *name;
+	gchar *human_name;
+	LdRectangle area;
+	LdPointArray *terminals;
+};
+
+
+G_END_DECLS
+
+#endif /* ! __LD_LUA_SYMBOL_PRIVATE_H__ */
+
diff --git a/liblogdiag/ld-lua-symbol.c b/liblogdiag/ld-lua-symbol.c
new file mode 100644
index 0000000..27a6279
--- /dev/null
+++ b/liblogdiag/ld-lua-symbol.c
@@ -0,0 +1,138 @@
+/*
+ * ld-lua-symbol.c
+ *
+ * This file is a part of logdiag.
+ * Copyright Přemysl Janouch 2010 - 2011. All rights reserved.
+ *
+ * See the file LICENSE for licensing information.
+ *
+ */
+
+#include "liblogdiag.h"
+#include "config.h"
+
+#include "ld-lua-private.h"
+#include "ld-lua-symbol-private.h"
+
+
+/**
+ * SECTION:ld-lua-symbol
+ * @short_description: A symbol.
+ * @see_also: #LdSymbol
+ *
+ * #LdLuaSymbol is an implementation of #LdSymbol.
+ */
+
+static void ld_lua_symbol_finalize (GObject *gobject);
+
+static const gchar *ld_lua_symbol_real_get_name (LdSymbol *symbol);
+static const gchar *ld_lua_symbol_real_get_human_name (LdSymbol *symbol);
+static void ld_lua_symbol_real_get_area (LdSymbol *symbol, LdRectangle *area);
+static const LdPointArray *ld_lua_symbol_real_get_terminals (LdSymbol *symbol);
+static void ld_lua_symbol_real_draw (LdSymbol *symbol, cairo_t *cr);
+
+
+G_DEFINE_TYPE (LdLuaSymbol, ld_lua_symbol, LD_TYPE_SYMBOL);
+
+static void
+ld_lua_symbol_class_init (LdLuaSymbolClass *klass)
+{
+	GObjectClass *object_class;
+
+	object_class = G_OBJECT_CLASS (klass);
+	object_class->finalize = ld_lua_symbol_finalize;
+
+	klass->parent_class.get_name = ld_lua_symbol_real_get_name;
+	klass->parent_class.get_human_name = ld_lua_symbol_real_get_human_name;
+	klass->parent_class.get_area = ld_lua_symbol_real_get_area;
+	klass->parent_class.get_terminals = ld_lua_symbol_real_get_terminals;
+	klass->parent_class.draw = ld_lua_symbol_real_draw;
+
+	g_type_class_add_private (klass, sizeof (LdLuaSymbolPrivate));
+}
+
+static void
+ld_lua_symbol_init (LdLuaSymbol *self)
+{
+	self->priv = G_TYPE_INSTANCE_GET_PRIVATE
+		(self, LD_TYPE_LUA_SYMBOL, LdLuaSymbolPrivate);
+}
+
+static void
+ld_lua_symbol_finalize (GObject *gobject)
+{
+	LdLuaSymbol *self;
+
+	self = LD_LUA_SYMBOL (gobject);
+
+	if (self->priv->lua)
+	{
+		ld_lua_private_unregister (self->priv->lua, self);
+		g_object_unref (self->priv->lua);
+	}
+
+	if (self->priv->name)
+		g_free (self->priv->name);
+	if (self->priv->human_name)
+		g_free (self->priv->human_name);
+
+	if (self->priv->terminals)
+		ld_point_array_free (self->priv->terminals);
+
+	/* Chain up to the parent class. */
+	G_OBJECT_CLASS (ld_lua_symbol_parent_class)->finalize (gobject);
+}
+
+
+static const gchar *
+ld_lua_symbol_real_get_name (LdSymbol *symbol)
+{
+	g_return_val_if_fail (LD_IS_LUA_SYMBOL (symbol), NULL);
+	return LD_LUA_SYMBOL (symbol)->priv->name;
+}
+
+static const gchar *
+ld_lua_symbol_real_get_human_name (LdSymbol *symbol)
+{
+	g_return_val_if_fail (LD_IS_LUA_SYMBOL (symbol), NULL);
+	return LD_LUA_SYMBOL (symbol)->priv->human_name;
+}
+
+static void
+ld_lua_symbol_real_get_area (LdSymbol *symbol, LdRectangle *area)
+{
+	LdLuaSymbol *self;
+
+	g_return_if_fail (LD_IS_LUA_SYMBOL (symbol));
+	g_return_if_fail (area != NULL);
+
+	self = LD_LUA_SYMBOL (symbol);
+	*area = self->priv->area;
+}
+
+static const LdPointArray *
+ld_lua_symbol_real_get_terminals (LdSymbol *symbol)
+{
+	LdLuaSymbol *self;
+
+	g_return_val_if_fail (LD_IS_LUA_SYMBOL (symbol), NULL);
+
+	self = LD_LUA_SYMBOL (symbol);
+	return self->priv->terminals;
+}
+
+static void
+ld_lua_symbol_real_draw (LdSymbol *symbol, cairo_t *cr)
+{
+	LdLuaSymbol *self;
+
+	g_return_if_fail (LD_IS_LUA_SYMBOL (symbol));
+	g_return_if_fail (cr != NULL);
+
+	self = LD_LUA_SYMBOL (symbol);
+
+	cairo_save (cr);
+	ld_lua_private_draw (self->priv->lua, self, cr);
+	cairo_restore (cr);
+}
+
diff --git a/liblogdiag/ld-lua-symbol.h b/liblogdiag/ld-lua-symbol.h
new file mode 100644
index 0000000..5f68b59
--- /dev/null
+++ b/liblogdiag/ld-lua-symbol.h
@@ -0,0 +1,60 @@
+/*
+ * ld-lua-symbol.h
+ *
+ * This file is a part of logdiag.
+ * Copyright Přemysl Janouch 2010. All rights reserved.
+ *
+ * See the file LICENSE for licensing information.
+ *
+ */
+
+#ifndef __LD_LUA_SYMBOL_H__
+#define __LD_LUA_SYMBOL_H__
+
+G_BEGIN_DECLS
+
+
+#define LD_TYPE_LUA_SYMBOL (ld_lua_symbol_get_type ())
+#define LD_LUA_SYMBOL(obj) (G_TYPE_CHECK_INSTANCE_CAST \
+	((obj), LD_TYPE_LUA_SYMBOL, LdLuaSymbol))
+#define LD_LUA_SYMBOL_CLASS(klass) (G_TYPE_CHECK_CLASS_CAST \
+	((klass), LD_TYPE_LUA_SYMBOL, LdLuaSymbolClass))
+#define LD_IS_LUA_SYMBOL(obj) (G_TYPE_CHECK_INSTANCE_TYPE \
+	((obj), LD_TYPE_LUA_SYMBOL))
+#define LD_IS_LUA_SYMBOL_CLASS(klass) (G_TYPE_CHECK_INSTANCE_TYPE \
+	((klass), LD_TYPE_LUA_SYMBOL))
+#define LD_LUA_SYMBOL_GET_CLASS(obj) (G_TYPE_INSTANCE_GET_CLASS \
+	((obj), LD_LUA_SYMBOL, LdLuaSymbolClass))
+
+typedef struct _LdLuaSymbol LdLuaSymbol;
+typedef struct _LdLuaSymbolPrivate LdLuaSymbolPrivate;
+typedef struct _LdLuaSymbolClass LdLuaSymbolClass;
+
+
+/**
+ * LdLuaSymbol:
+ */
+struct _LdLuaSymbol
+{
+/*< private >*/
+	LdSymbol parent_instance;
+	LdLuaSymbolPrivate *priv;
+};
+
+/**
+ * LdLuaSymbolClass:
+ * @parent_class: The parent class.
+ */
+struct _LdLuaSymbolClass
+{
+	LdSymbolClass parent_class;
+};
+
+
+GType ld_lua_symbol_get_type (void) G_GNUC_CONST;
+
+
+G_END_DECLS
+
+#endif /* ! __LD_LUA_SYMBOL_H__ */
+
diff --git a/liblogdiag/ld-lua.c b/liblogdiag/ld-lua.c
new file mode 100644
index 0000000..47a41b5
--- /dev/null
+++ b/liblogdiag/ld-lua.c
@@ -0,0 +1,808 @@
+/*
+ * ld-lua.c
+ *
+ * This file is a part of logdiag.
+ * Copyright Přemysl Janouch 2010 - 2011. All rights reserved.
+ *
+ * See the file LICENSE for licensing information.
+ *
+ */
+
+#include <lua.h>
+#include <lualib.h>
+#include <lauxlib.h>
+
+#include "liblogdiag.h"
+#include "config.h"
+
+#include "ld-lua-private.h"
+#include "ld-lua-symbol-private.h"
+
+
+/**
+ * SECTION:ld-lua
+ * @short_description: Lua symbol engine.
+ * @see_also: #LdLuaSymbol
+ *
+ * #LdLua is a symbol engine that uses Lua scripts to manage symbols.
+ */
+
+/*
+ * LdLuaPrivate:
+ * @L: Lua state.
+ *
+ * The library contains the real function for rendering.
+ */
+struct _LdLuaPrivate
+{
+	lua_State *L;
+};
+
+/* registry.logdiag_symbols
+ *   -> A table indexed by pointers to LdLuaSymbol objects
+ * registry.logdiag_symbols.object.render(cr)
+ *   -> The rendering function
+ */
+
+#define LD_LUA_LIBRARY_NAME "logdiag"
+#define LD_LUA_DATA_INDEX LD_LUA_LIBRARY_NAME "_data"
+#define LD_LUA_SYMBOLS_INDEX LD_LUA_LIBRARY_NAME "_symbols"
+
+/*
+ * LdLuaData:
+ * @self: A reference to self.
+ * @load_callback: A callback for newly registered symbols.
+ * @load_user_data: User data to be passed to the callback.
+ *
+ * Full user data to be stored in Lua registry.
+ */
+typedef struct _LdLuaData LdLuaData;
+
+struct _LdLuaData
+{
+	LdLua *self;
+	LdLuaLoadCallback load_callback;
+	gpointer load_user_data;
+};
+
+typedef struct _LdLuaDrawData LdLuaDrawData;
+
+struct _LdLuaDrawData
+{
+	LdLuaSymbol *symbol;
+	cairo_t *cr;
+	unsigned save_count;
+};
+
+static void ld_lua_finalize (GObject *gobject);
+
+static void *ld_lua_alloc (void *ud, void *ptr, size_t osize, size_t nsize);
+
+static int ld_lua_private_draw_cb (lua_State *L);
+static int ld_lua_private_unregister_cb (lua_State *L);
+
+static int ld_lua_logdiag_register (lua_State *L);
+static int process_registration (lua_State *L);
+static gchar *get_translation (lua_State *L, int index);
+static gboolean read_symbol_area (lua_State *L, int index, LdRectangle *area);
+static gboolean read_terminals (lua_State *L, int index,
+	LdPointArray **terminals);
+
+static void push_cairo_object (lua_State *L, LdLuaDrawData *draw_data);
+static gdouble get_cairo_scale (cairo_t *cr);
+static int ld_lua_cairo_save (lua_State *L);
+static int ld_lua_cairo_restore (lua_State *L);
+static int ld_lua_cairo_get_line_width (lua_State *L);
+static int ld_lua_cairo_set_line_width (lua_State *L);
+static int ld_lua_cairo_move_to (lua_State *L);
+static int ld_lua_cairo_line_to (lua_State *L);
+static int ld_lua_cairo_curve_to (lua_State *L);
+static int ld_lua_cairo_arc (lua_State *L);
+static int ld_lua_cairo_arc_negative (lua_State *L);
+static int ld_lua_cairo_new_path (lua_State *L);
+static int ld_lua_cairo_new_sub_path (lua_State *L);
+static int ld_lua_cairo_close_path (lua_State *L);
+static int ld_lua_cairo_stroke (lua_State *L);
+static int ld_lua_cairo_stroke_preserve (lua_State *L);
+static int ld_lua_cairo_fill (lua_State *L);
+static int ld_lua_cairo_fill_preserve (lua_State *L);
+static int ld_lua_cairo_clip (lua_State *L);
+static int ld_lua_cairo_clip_preserve (lua_State *L);
+
+
+static luaL_Reg ld_lua_logdiag_lib[] =
+{
+	{"register", ld_lua_logdiag_register},
+	{NULL, NULL}
+};
+
+static luaL_Reg ld_lua_cairo_table[] =
+{
+	{"save", ld_lua_cairo_save},
+	{"restore", ld_lua_cairo_restore},
+	{"get_line_width", ld_lua_cairo_get_line_width},
+	{"set_line_width", ld_lua_cairo_set_line_width},
+	{"move_to", ld_lua_cairo_move_to},
+	{"line_to", ld_lua_cairo_line_to},
+	{"curve_to", ld_lua_cairo_curve_to},
+	{"arc", ld_lua_cairo_arc},
+	{"arc_negative", ld_lua_cairo_arc_negative},
+	{"new_path", ld_lua_cairo_new_path},
+	{"new_sub_path", ld_lua_cairo_new_sub_path},
+	{"close_path", ld_lua_cairo_close_path},
+	{"stroke", ld_lua_cairo_stroke},
+	{"stroke_preserve", ld_lua_cairo_stroke_preserve},
+	{"fill", ld_lua_cairo_fill},
+	{"fill_preserve", ld_lua_cairo_fill_preserve},
+	{"clip", ld_lua_cairo_clip},
+	{"clip_preserve", ld_lua_cairo_clip_preserve},
+	{NULL, NULL}
+};
+
+
+/* ===== Generic =========================================================== */
+
+G_DEFINE_TYPE (LdLua, ld_lua, G_TYPE_OBJECT);
+
+static void
+ld_lua_class_init (LdLuaClass *klass)
+{
+	GObjectClass *object_class;
+
+	object_class = G_OBJECT_CLASS (klass);
+	object_class->finalize = ld_lua_finalize;
+
+	g_type_class_add_private (klass, sizeof (LdLuaPrivate));
+}
+
+static void
+ld_lua_init (LdLua *self)
+{
+	lua_State *L;
+	LdLuaData *ud;
+
+	self->priv = G_TYPE_INSTANCE_GET_PRIVATE
+		(self, LD_TYPE_LUA, LdLuaPrivate);
+
+	L = self->priv->L = lua_newstate (ld_lua_alloc, NULL);
+	g_return_if_fail (L != NULL);
+
+	/* TODO: lua_atpanic () */
+
+	/* Load some safe libraries. */
+	lua_pushcfunction (L, luaopen_string);
+	lua_call (L, 0, 0);
+
+	lua_pushcfunction (L, luaopen_table);
+	lua_call (L, 0, 0);
+
+	lua_pushcfunction (L, luaopen_math);
+	lua_call (L, 0, 0);
+
+	/* Load the application library. */
+	luaL_register (L, LD_LUA_LIBRARY_NAME, ld_lua_logdiag_lib);
+
+	/* Store user data to the registry. */
+	ud = lua_newuserdata (L, sizeof (LdLuaData));
+	ud->self = self;
+	ud->load_callback = NULL;
+	ud->load_user_data = NULL;
+
+	lua_setfield (L, LUA_REGISTRYINDEX, LD_LUA_DATA_INDEX);
+
+	/* Create an empty symbol table. */
+	lua_newtable (L);
+	lua_setfield (L, LUA_REGISTRYINDEX, LD_LUA_SYMBOLS_INDEX);
+}
+
+static void
+ld_lua_finalize (GObject *gobject)
+{
+	LdLua *self;
+
+	self = LD_LUA (gobject);
+	lua_close (self->priv->L);
+
+	/* Chain up to the parent class. */
+	G_OBJECT_CLASS (ld_lua_parent_class)->finalize (gobject);
+}
+
+/**
+ * ld_lua_new:
+ *
+ * Create an instance of #LdLua.
+ */
+LdLua *
+ld_lua_new (void)
+{
+	return g_object_new (LD_TYPE_LUA, NULL);
+}
+
+static void *
+ld_lua_alloc (void *ud, void *ptr, size_t osize, size_t nsize)
+{
+	if (!nsize)
+	{
+		g_free (ptr);
+		return NULL;
+	}
+	else
+		return g_try_realloc (ptr, nsize);
+}
+
+/**
+ * ld_lua_check_file:
+ * @self: An #LdLua object.
+ * @filename: The file to be checked.
+ *
+ * Check if the given filename can be loaded by #LdLua.
+ */
+gboolean
+ld_lua_check_file (LdLua *self, const gchar *filename)
+{
+	g_return_val_if_fail (LD_IS_LUA (self), FALSE);
+	g_return_val_if_fail (filename != NULL, FALSE);
+
+	return g_str_has_suffix (filename, ".lua")
+		&& g_file_test (filename, G_FILE_TEST_IS_REGULAR);
+}
+
+/**
+ * ld_lua_load_file:
+ * @self: An #LdLua object.
+ * @filename: The file to be loaded.
+ * @callback: A callback for newly registered symbols.
+ * The callee is responsible for referencing the symbol.
+ * @user_data: User data to be passed to the callback.
+ *
+ * Loads a file and creates #LdLuaSymbol objects for contained symbols.
+ *
+ * Returns: TRUE if no error has occured, FALSE otherwise.
+ */
+gboolean
+ld_lua_load_file (LdLua *self, const gchar *filename,
+	LdLuaLoadCallback callback, gpointer user_data)
+{
+	gint retval;
+	LdLuaData *ud;
+
+	g_return_val_if_fail (LD_IS_LUA (self), FALSE);
+	g_return_val_if_fail (filename != NULL, FALSE);
+	g_return_val_if_fail (callback != NULL, FALSE);
+
+	/* XXX: If something from the following fails, Lua will call exit(). */
+	lua_getfield (self->priv->L, LUA_REGISTRYINDEX, LD_LUA_DATA_INDEX);
+	ud = lua_touserdata (self->priv->L, -1);
+	lua_pop (self->priv->L, 1);
+	g_return_val_if_fail (ud != NULL, FALSE);
+
+	ud->load_callback = callback;
+	ud->load_user_data = user_data;
+
+	retval = luaL_loadfile (self->priv->L, filename);
+	if (retval)
+		goto ld_lua_lftc_fail;
+
+	retval = lua_pcall (self->priv->L, 0, 0, 0);
+	if (retval)
+		goto ld_lua_lftc_fail;
+
+	ud->load_callback = NULL;
+	ud->load_user_data = NULL;
+	return TRUE;
+
+ld_lua_lftc_fail:
+	g_warning ("Lua error: %s", lua_tostring (self->priv->L, -1));
+	lua_remove (self->priv->L, -1);
+
+	ud->load_callback = NULL;
+	ud->load_user_data = NULL;
+	return FALSE;
+}
+
+/* ===== LdLuaSymbol callbacks ============================================= */
+
+/**
+ * ld_lua_private_draw:
+ * @self: An #LdLua object.
+ * @symbol: A symbol to be drawn.
+ * @cr: A Cairo context to be drawn onto.
+ *
+ * Draw a symbol onto a Cairo context.
+ */
+void
+ld_lua_private_draw (LdLua *self, LdLuaSymbol *symbol, cairo_t *cr)
+{
+	LdLuaDrawData data;
+
+	g_return_if_fail (LD_IS_LUA (self));
+	g_return_if_fail (LD_IS_LUA_SYMBOL (symbol));
+	g_return_if_fail (cr != NULL);
+
+	data.symbol = symbol;
+	data.cr = cr;
+	data.save_count = 0;
+
+	if (lua_cpcall (self->priv->L, ld_lua_private_draw_cb, &data))
+	{
+		g_warning ("Lua error: %s", lua_tostring (self->priv->L, -1));
+		lua_pop (self->priv->L, 1);
+	}
+
+	while (data.save_count--)
+		cairo_restore (cr);
+}
+
+static int
+ld_lua_private_draw_cb (lua_State *L)
+{
+	LdLuaDrawData *data;
+
+	data = lua_touserdata (L, -1);
+
+	/* Retrieve the function for rendering from the registry. */
+	lua_getfield (L, LUA_REGISTRYINDEX, LD_LUA_SYMBOLS_INDEX);
+	lua_pushlightuserdata (L, data->symbol);
+	lua_gettable (L, -2);
+
+	luaL_checktype (L, -1, LUA_TTABLE);
+	lua_getfield (L, -1, "render");
+	luaL_checktype (L, -1, LUA_TFUNCTION);
+
+	/* Call the function do draw the symbol. */
+	push_cairo_object (L, data);
+	lua_pcall (L, 1, 0, 0);
+	return 0;
+}
+
+/**
+ * ld_lua_private_unregister:
+ * @self: An #LdLua object.
+ * @symbol: A symbol to be unregistered.
+ *
+ * Unregister a symbol from the internal Lua state.
+ */
+void
+ld_lua_private_unregister (LdLua *self, LdLuaSymbol *symbol)
+{
+	g_return_if_fail (LD_IS_LUA (self));
+	g_return_if_fail (LD_IS_LUA_SYMBOL (symbol));
+
+	if (lua_cpcall (self->priv->L, ld_lua_private_unregister_cb, symbol))
+	{
+		g_warning ("Lua error: %s", lua_tostring (self->priv->L, -1));
+		lua_pop (self->priv->L, 1);
+	}
+}
+
+static int
+ld_lua_private_unregister_cb (lua_State *L)
+{
+	/* Set the entry in the symbol table to nil. */
+	lua_getfield (L, LUA_REGISTRYINDEX, LD_LUA_SYMBOLS_INDEX);
+	lua_insert (L, -2);
+	lua_pushnil (L);
+	lua_settable (L, -3);
+	return 0;
+}
+
+/* ===== Application library =============================================== */
+
+static int
+ld_lua_logdiag_register (lua_State *L)
+{
+	LdLuaData *ud;
+	LdLuaSymbol *symbol;
+
+	lua_getfield (L, LUA_REGISTRYINDEX, LD_LUA_DATA_INDEX);
+	ud = lua_touserdata (L, -1);
+	lua_pop (L, 1);
+	g_return_val_if_fail (ud != NULL, 0);
+
+	/* Use a protected environment, so script errors won't cause leaking
+	 * of the symbol object. Only a failure of the last three function calls
+	 * before lua_pcall() may cause the symbol to leak.
+	 */
+	lua_checkstack (L, 3);
+	symbol = g_object_new (LD_TYPE_LUA_SYMBOL, NULL);
+
+	lua_pushlightuserdata (L, symbol);
+	lua_pushcclosure (L, process_registration, 1);
+	lua_insert (L, 1);
+
+	/* On the stack, there are function arguments plus the function itself. */
+	if (lua_pcall (L, lua_gettop (L) - 1, 0, 0))
+	{
+		luaL_where (L, 1);
+		lua_insert (L, -2);
+		lua_concat (L, 2);
+
+		g_warning ("Lua symbol registration failed: %s",
+			lua_tostring (L, -1));
+		lua_pushboolean (L, FALSE);
+	}
+	else
+	{
+		/* We don't want an extra LdLua reference either. */
+		symbol->priv->lua = ud->self;
+		g_object_ref (ud->self);
+
+		ud->load_callback (LD_SYMBOL (symbol), ud->load_user_data);
+		lua_pushboolean (L, TRUE);
+	}
+	g_object_unref (symbol);
+
+	return 1;
+}
+
+/*
+ * process_registration:
+ * @L: A Lua state.
+ *
+ * Parse arguments, write them to a symbol object and register the object.
+ */
+static int
+process_registration (lua_State *L)
+{
+	LdLuaSymbol *symbol;
+	gchar *human_name;
+
+	int i, type, types[] =
+		{LUA_TSTRING, LUA_TTABLE, LUA_TTABLE, LUA_TTABLE, LUA_TFUNCTION};
+	int n_args_needed = sizeof (types) / sizeof (int);
+
+	if (lua_gettop (L) < n_args_needed)
+		return luaL_error (L, "Too few arguments.");
+
+	for (i = 0; i < n_args_needed; i++)
+		if ((type = lua_type (L, i + 1)) != types[i])
+			return luaL_error (L, "Bad type of argument #%d."
+				" Expected %s, got %s.", i + 1,
+				lua_typename (L, types[i]), lua_typename (L, type));
+
+	symbol = LD_LUA_SYMBOL (lua_touserdata (L, lua_upvalueindex (1)));
+	symbol->priv->name = g_strdup (lua_tostring (L, 1));
+
+	human_name = get_translation (L, 2);
+	if (!human_name)
+		human_name = g_strdup (symbol->priv->name);
+	symbol->priv->human_name = human_name;
+
+	if (!read_symbol_area (L, 3, &symbol->priv->area))
+		return luaL_error (L, "Malformed symbol area array.");
+	if (!read_terminals (L, 4, &symbol->priv->terminals))
+		return luaL_error (L, "Malformed terminals array.");
+
+	lua_getfield (L, LUA_REGISTRYINDEX, LD_LUA_SYMBOLS_INDEX);
+	lua_pushlightuserdata (L, symbol);
+
+	lua_newtable (L);
+	lua_pushvalue (L, 5);
+	lua_setfield (L, -2, "render");
+
+	lua_settable (L, -3);
+	return 0;
+}
+
+/*
+ * get_translation:
+ * @L: A Lua state.
+ * @index: Stack index of the table.
+ *
+ * Select an applicable translation from a table.
+ * The return value has to be freed with g_free().
+ *
+ * Return value: The translation, if found. If none was found, returns NULL.
+ */
+static gchar *
+get_translation (lua_State *L, int index)
+{
+	const gchar *const *lang;
+	gchar *result;
+
+	for (lang = g_get_language_names (); *lang; lang++)
+	{
+		lua_getfield (L, 2, *lang);
+		if (lua_isstring (L, -1))
+		{
+			result = g_strdup (lua_tostring (L, -1));
+			lua_pop (L, 1);
+			return result;
+		}
+		lua_pop (L, 1);
+	}
+	return NULL;
+}
+
+/*
+ * read_symbol_area:
+ * @L: A Lua state.
+ * @index: Stack index of the table.
+ * @area: Where the area will be returned.
+ *
+ * Read a symbol area from a Lua table.
+ *
+ * Return value: TRUE on success, FALSE on failure.
+ */
+static gboolean
+read_symbol_area (lua_State *L, int index, LdRectangle *area)
+{
+	lua_Number x1, x2, y1, y2;
+
+	if (lua_objlen (L, index) != 4)
+		return FALSE;
+
+	lua_rawgeti (L, index, 1);
+	if (!lua_isnumber (L, -1))
+		return FALSE;
+	x1 = lua_tonumber (L, -1);
+
+	lua_rawgeti (L, index, 2);
+	if (!lua_isnumber (L, -1))
+		return FALSE;
+	y1 = lua_tonumber (L, -1);
+
+	lua_rawgeti (L, index, 3);
+	if (!lua_isnumber (L, -1))
+		return FALSE;
+	x2 = lua_tonumber (L, -1);
+
+	lua_rawgeti (L, index, 4);
+	if (!lua_isnumber (L, -1))
+		return FALSE;
+	y2 = lua_tonumber (L, -1);
+
+	area->x = MIN (x1, x2);
+	area->y = MIN (y1, y2);
+	area->width = ABS (x2 - x1);
+	area->height = ABS (y2 - y1);
+
+	lua_pop (L, 4);
+	return TRUE;
+}
+
+/*
+ * read_terminals:
+ * @L: A Lua state.
+ * @index: Stack index of the table.
+ * @area: Where the point array will be returned.
+ *
+ * Read symbol terminals from a Lua table.
+ *
+ * Return value: TRUE on success, FALSE on failure.
+ */
+static gboolean
+read_terminals (lua_State *L, int index, LdPointArray **terminals)
+{
+	LdPointArray *points;
+	size_t num_points;
+	unsigned i = 0;
+
+	num_points = lua_objlen (L, index);
+	points = ld_point_array_new (num_points);
+
+	lua_pushnil (L);
+	while (lua_next (L, index) != 0)
+	{
+		g_assert (i < num_points);
+
+		if (!lua_istable (L, -1) || lua_objlen (L, -1) != 2)
+			goto read_terminals_fail;
+
+		lua_rawgeti (L, -1, 1);
+		if (!lua_isnumber (L, -1))
+			goto read_terminals_fail;
+		points->points[i].x = lua_tonumber (L, -1);
+		lua_pop (L, 1);
+
+		lua_rawgeti (L, -1, 2);
+		if (!lua_isnumber (L, -1))
+			goto read_terminals_fail;
+		points->points[i].y = lua_tonumber (L, -1);
+
+		lua_pop (L, 2);
+		i++;
+	}
+	*terminals = points;
+	return TRUE;
+
+read_terminals_fail:
+	ld_point_array_free (points);
+	*terminals = NULL;
+	return FALSE;
+}
+
+
+/* ===== Cairo ============================================================= */
+
+static void
+push_cairo_object (lua_State *L, LdLuaDrawData *draw_data)
+{
+	luaL_Reg *fn;
+
+	/* Create a table. */
+	lua_newtable (L);
+
+	/* Add methods. */
+	/* XXX: The light user data pointer gets invalid after the end of
+	 *      "render" function invocation. If the script stores the "cr" object
+	 *      in some global variable and then tries to reuse it the next time,
+	 *      the application may go SIGSEGV.
+	 *
+	 *      The solution is creating a full user data instead, referencing
+	 *      the cairo object and dereferencing it upon garbage collection
+	 *      of the user data object.
+	 */
+	for (fn = ld_lua_cairo_table; fn->name; fn++)
+	{
+		lua_pushlightuserdata (L, draw_data);
+		lua_pushcclosure (L, fn->func, 1);
+		lua_setfield (L, -2, fn->name);
+	}
+}
+
+static gdouble
+get_cairo_scale (cairo_t *cr)
+{
+	double dx = 1, dy = 0;
+
+	cairo_user_to_device_distance (cr, &dx, &dy);
+	return dx;
+}
+
+#define LD_LUA_CAIRO_TRIVIAL(name) \
+static int \
+ld_lua_cairo_ ## name (lua_State *L) \
+{ \
+	LdLuaDrawData *data; \
+	data = lua_touserdata (L, lua_upvalueindex (1)); \
+	cairo_ ## name (data->cr); \
+	return 0; \
+}
+
+LD_LUA_CAIRO_TRIVIAL (new_path)
+LD_LUA_CAIRO_TRIVIAL (new_sub_path)
+LD_LUA_CAIRO_TRIVIAL (close_path)
+
+LD_LUA_CAIRO_TRIVIAL (stroke)
+LD_LUA_CAIRO_TRIVIAL (stroke_preserve)
+LD_LUA_CAIRO_TRIVIAL (fill)
+LD_LUA_CAIRO_TRIVIAL (fill_preserve)
+LD_LUA_CAIRO_TRIVIAL (clip)
+LD_LUA_CAIRO_TRIVIAL (clip_preserve)
+
+static int
+ld_lua_cairo_save (lua_State *L)
+{
+	LdLuaDrawData *data;
+
+	data = lua_touserdata (L, lua_upvalueindex (1));
+	if (data->save_count + 1)
+	{
+		data->save_count++;
+		cairo_save (data->cr);
+	}
+	return 0;
+}
+
+static int
+ld_lua_cairo_restore (lua_State *L)
+{
+	LdLuaDrawData *data;
+
+	data = lua_touserdata (L, lua_upvalueindex (1));
+	if (data->save_count)
+	{
+		data->save_count--;
+		cairo_restore (data->cr);
+	}
+	return 0;
+}
+
+static int
+ld_lua_cairo_get_line_width (lua_State *L)
+{
+	LdLuaDrawData *data;
+
+	data = lua_touserdata (L, lua_upvalueindex (1));
+	lua_pushnumber (L, cairo_get_line_width (data->cr)
+		* get_cairo_scale (data->cr));
+	return 1;
+}
+
+static int
+ld_lua_cairo_set_line_width (lua_State *L)
+{
+	LdLuaDrawData *data;
+
+	data = lua_touserdata (L, lua_upvalueindex (1));
+	cairo_set_line_width (data->cr, luaL_checknumber (L, 1)
+		/ get_cairo_scale (data->cr));
+	return 0;
+}
+
+static int
+ld_lua_cairo_move_to (lua_State *L)
+{
+	LdLuaDrawData *data;
+	lua_Number x, y;
+
+	data = lua_touserdata (L, lua_upvalueindex (1));
+
+	x = luaL_checknumber (L, 1);
+	y = luaL_checknumber (L, 2);
+
+	cairo_move_to (data->cr, x, y);
+	return 0;
+}
+
+static int
+ld_lua_cairo_line_to (lua_State *L)
+{
+	LdLuaDrawData *data;
+	lua_Number x, y;
+
+	data = lua_touserdata (L, lua_upvalueindex (1));
+
+	x = luaL_checknumber (L, 1);
+	y = luaL_checknumber (L, 2);
+
+	cairo_line_to (data->cr, x, y);
+	return 0;
+}
+
+static int
+ld_lua_cairo_curve_to (lua_State *L)
+{
+	LdLuaDrawData *data;
+	lua_Number x1, y1, x2, y2, x3, y3;
+
+	data = lua_touserdata (L, lua_upvalueindex (1));
+
+	x1 = luaL_checknumber (L, 1);
+	y1 = luaL_checknumber (L, 2);
+	x2 = luaL_checknumber (L, 3);
+	y2 = luaL_checknumber (L, 4);
+	x3 = luaL_checknumber (L, 5);
+	y3 = luaL_checknumber (L, 6);
+
+	cairo_curve_to (data->cr, x1, y1, x2, y2, x3, y3);
+	return 0;
+}
+
+static int
+ld_lua_cairo_arc (lua_State *L)
+{
+	LdLuaDrawData *data;
+	lua_Number xc, yc, radius, angle1, angle2;
+
+	data = lua_touserdata (L, lua_upvalueindex (1));
+
+	xc = luaL_checknumber (L, 1);
+	yc = luaL_checknumber (L, 2);
+	radius = luaL_checknumber (L, 3);
+	angle1 = luaL_checknumber (L, 4);
+	angle2 = luaL_checknumber (L, 5);
+
+	cairo_arc (data->cr, xc, yc, radius, angle1, angle2);
+	return 0;
+}
+
+static int
+ld_lua_cairo_arc_negative (lua_State *L)
+{
+	LdLuaDrawData *data;
+	lua_Number xc, yc, radius, angle1, angle2;
+
+	data = lua_touserdata (L, lua_upvalueindex (1));
+
+	xc = luaL_checknumber (L, 1);
+	yc = luaL_checknumber (L, 2);
+	radius = luaL_checknumber (L, 3);
+	angle1 = luaL_checknumber (L, 4);
+	angle2 = luaL_checknumber (L, 5);
+
+	cairo_arc_negative (data->cr, xc, yc, radius, angle1, angle2);
+	return 0;
+}
+
diff --git a/liblogdiag/ld-lua.h b/liblogdiag/ld-lua.h
new file mode 100644
index 0000000..b207d66
--- /dev/null
+++ b/liblogdiag/ld-lua.h
@@ -0,0 +1,70 @@
+/*
+ * ld-lua.h
+ *
+ * This file is a part of logdiag.
+ * Copyright Přemysl Janouch 2010. All rights reserved.
+ *
+ * See the file LICENSE for licensing information.
+ *
+ */
+
+#ifndef __LD_LUA_H__
+#define __LD_LUA_H__
+
+G_BEGIN_DECLS
+
+
+#define LD_TYPE_LUA (ld_lua_get_type ())
+#define LD_LUA(obj) (G_TYPE_CHECK_INSTANCE_CAST \
+	((obj), LD_TYPE_LUA, LdLua))
+#define LD_LUA_CLASS(klass) (G_TYPE_CHECK_CLASS_CAST \
+	((klass), LD_TYPE_LUA, LdLuaClass))
+#define LD_IS_LUA(obj) (G_TYPE_CHECK_INSTANCE_TYPE \
+	((obj), LD_TYPE_LUA))
+#define LD_IS_LUA_CLASS(klass) (G_TYPE_CHECK_INSTANCE_TYPE \
+	((klass), LD_TYPE_LUA))
+#define LD_LUA_GET_CLASS(obj) (G_TYPE_INSTANCE_GET_CLASS \
+	((obj), LD_LUA, LdLuaClass))
+
+typedef struct _LdLua LdLua;
+typedef struct _LdLuaPrivate LdLuaPrivate;
+typedef struct _LdLuaClass LdLuaClass;
+
+
+struct _LdLua
+{
+/*< private >*/
+	GObject parent_instance;
+	LdLuaPrivate *priv;
+};
+
+/* TODO: A virtual superclass, so other engines can be used. */
+struct _LdLuaClass
+{
+/*< private >*/
+	GObjectClass parent_class;
+};
+
+
+/**
+ * LdLuaLoadCallback:
+ * @symbol: The symbol that has been created.
+ * @user_data: User data passed to ld_lua_load_file().
+ *
+ * A callback function that is called when a symbol is created.
+ */
+typedef void (*LdLuaLoadCallback) (LdSymbol *symbol, gpointer user_data);
+
+
+GType ld_lua_get_type (void) G_GNUC_CONST;
+
+LdLua *ld_lua_new (void);
+gboolean ld_lua_check_file (LdLua *self, const gchar *filename);
+gboolean ld_lua_load_file (LdLua *self, const gchar *filename,
+	LdLuaLoadCallback callback, gpointer user_data);
+
+
+G_END_DECLS
+
+#endif /* ! __LD_LUA_H__ */
+
diff --git a/liblogdiag/ld-marshal.c b/liblogdiag/ld-marshal.c
new file mode 100644
index 0000000..ac88836
--- /dev/null
+++ b/liblogdiag/ld-marshal.c
@@ -0,0 +1,88 @@
+
+#include	<glib-object.h>
+
+
+#ifdef G_ENABLE_DEBUG
+#define g_marshal_value_peek_boolean(v)  g_value_get_boolean (v)
+#define g_marshal_value_peek_char(v)     g_value_get_char (v)
+#define g_marshal_value_peek_uchar(v)    g_value_get_uchar (v)
+#define g_marshal_value_peek_int(v)      g_value_get_int (v)
+#define g_marshal_value_peek_uint(v)     g_value_get_uint (v)
+#define g_marshal_value_peek_long(v)     g_value_get_long (v)
+#define g_marshal_value_peek_ulong(v)    g_value_get_ulong (v)
+#define g_marshal_value_peek_int64(v)    g_value_get_int64 (v)
+#define g_marshal_value_peek_uint64(v)   g_value_get_uint64 (v)
+#define g_marshal_value_peek_enum(v)     g_value_get_enum (v)
+#define g_marshal_value_peek_flags(v)    g_value_get_flags (v)
+#define g_marshal_value_peek_float(v)    g_value_get_float (v)
+#define g_marshal_value_peek_double(v)   g_value_get_double (v)
+#define g_marshal_value_peek_string(v)   (char*) g_value_get_string (v)
+#define g_marshal_value_peek_param(v)    g_value_get_param (v)
+#define g_marshal_value_peek_boxed(v)    g_value_get_boxed (v)
+#define g_marshal_value_peek_pointer(v)  g_value_get_pointer (v)
+#define g_marshal_value_peek_object(v)   g_value_get_object (v)
+#define g_marshal_value_peek_variant(v)  g_value_get_variant (v)
+#else /* !G_ENABLE_DEBUG */
+/* WARNING: This code accesses GValues directly, which is UNSUPPORTED API.
+ *          Do not access GValues directly in your code. Instead, use the
+ *          g_value_get_*() functions
+ */
+#define g_marshal_value_peek_boolean(v)  (v)->data[0].v_int
+#define g_marshal_value_peek_char(v)     (v)->data[0].v_int
+#define g_marshal_value_peek_uchar(v)    (v)->data[0].v_uint
+#define g_marshal_value_peek_int(v)      (v)->data[0].v_int
+#define g_marshal_value_peek_uint(v)     (v)->data[0].v_uint
+#define g_marshal_value_peek_long(v)     (v)->data[0].v_long
+#define g_marshal_value_peek_ulong(v)    (v)->data[0].v_ulong
+#define g_marshal_value_peek_int64(v)    (v)->data[0].v_int64
+#define g_marshal_value_peek_uint64(v)   (v)->data[0].v_uint64
+#define g_marshal_value_peek_enum(v)     (v)->data[0].v_long
+#define g_marshal_value_peek_flags(v)    (v)->data[0].v_ulong
+#define g_marshal_value_peek_float(v)    (v)->data[0].v_float
+#define g_marshal_value_peek_double(v)   (v)->data[0].v_double
+#define g_marshal_value_peek_string(v)   (v)->data[0].v_pointer
+#define g_marshal_value_peek_param(v)    (v)->data[0].v_pointer
+#define g_marshal_value_peek_boxed(v)    (v)->data[0].v_pointer
+#define g_marshal_value_peek_pointer(v)  (v)->data[0].v_pointer
+#define g_marshal_value_peek_object(v)   (v)->data[0].v_pointer
+#define g_marshal_value_peek_variant(v)  (v)->data[0].v_pointer
+#endif /* !G_ENABLE_DEBUG */
+
+
+/* VOID:OBJECT,OBJECT (ld-marshal.list:1) */
+void
+g_cclosure_user_marshal_VOID__OBJECT_OBJECT (GClosure     *closure,
+                                             GValue       *return_value G_GNUC_UNUSED,
+                                             guint         n_param_values,
+                                             const GValue *param_values,
+                                             gpointer      invocation_hint G_GNUC_UNUSED,
+                                             gpointer      marshal_data)
+{
+  typedef void (*GMarshalFunc_VOID__OBJECT_OBJECT) (gpointer     data1,
+                                                    gpointer     arg_1,
+                                                    gpointer     arg_2,
+                                                    gpointer     data2);
+  register GMarshalFunc_VOID__OBJECT_OBJECT callback;
+  register GCClosure *cc = (GCClosure*) closure;
+  register gpointer data1, data2;
+
+  g_return_if_fail (n_param_values == 3);
+
+  if (G_CCLOSURE_SWAP_DATA (closure))
+    {
+      data1 = closure->data;
+      data2 = g_value_peek_pointer (param_values + 0);
+    }
+  else
+    {
+      data1 = g_value_peek_pointer (param_values + 0);
+      data2 = closure->data;
+    }
+  callback = (GMarshalFunc_VOID__OBJECT_OBJECT) (marshal_data ? marshal_data : cc->callback);
+
+  callback (data1,
+            g_marshal_value_peek_object (param_values + 1),
+            g_marshal_value_peek_object (param_values + 2),
+            data2);
+}
+
diff --git a/liblogdiag/ld-marshal.h b/liblogdiag/ld-marshal.h
new file mode 100644
index 0000000..545735a
--- /dev/null
+++ b/liblogdiag/ld-marshal.h
@@ -0,0 +1,20 @@
+
+#ifndef __g_cclosure_user_marshal_MARSHAL_H__
+#define __g_cclosure_user_marshal_MARSHAL_H__
+
+#include	<glib-object.h>
+
+G_BEGIN_DECLS
+
+/* VOID:OBJECT,OBJECT (ld-marshal.list:1) */
+extern void g_cclosure_user_marshal_VOID__OBJECT_OBJECT (GClosure     *closure,
+                                                         GValue       *return_value,
+                                                         guint         n_param_values,
+                                                         const GValue *param_values,
+                                                         gpointer      invocation_hint,
+                                                         gpointer      marshal_data);
+
+G_END_DECLS
+
+#endif /* __g_cclosure_user_marshal_MARSHAL_H__ */
+
diff --git a/liblogdiag/ld-marshal.list b/liblogdiag/ld-marshal.list
new file mode 100644
index 0000000..38076d6
--- /dev/null
+++ b/liblogdiag/ld-marshal.list
@@ -0,0 +1 @@
+VOID:OBJECT,OBJECT
diff --git a/liblogdiag/ld-symbol-category.c b/liblogdiag/ld-symbol-category.c
new file mode 100644
index 0000000..e4b86a9
--- /dev/null
+++ b/liblogdiag/ld-symbol-category.c
@@ -0,0 +1,339 @@
+/*
+ * ld-symbol-category.c
+ *
+ * This file is a part of logdiag.
+ * Copyright Přemysl Janouch 2010 - 2011. All rights reserved.
+ *
+ * See the file LICENSE for licensing information.
+ *
+ */
+
+#include "liblogdiag.h"
+#include "config.h"
+
+
+/**
+ * SECTION:ld-symbol-category
+ * @short_description: A category of symbols.
+ * @see_also: #LdSymbol, #LdLibrary
+ *
+ * #LdSymbolCategory represents a category of #LdSymbol objects.
+ */
+
+/*
+ * LdSymbolCategoryPrivate:
+ * @name: The name of this category.
+ * @image_path: Path to the image for this category.
+ * @children: Children of this category.
+ */
+struct _LdSymbolCategoryPrivate
+{
+	gchar *name;
+	gchar *human_name;
+	gchar *image_path;
+	GSList *children;
+};
+
+enum
+{
+	PROP_0,
+	PROP_NAME,
+	PROP_HUMAN_NAME,
+	PROP_IMAGE_PATH
+};
+
+static void ld_symbol_category_get_property (GObject *object, guint property_id,
+	GValue *value, GParamSpec *pspec);
+static void ld_symbol_category_set_property (GObject *object, guint property_id,
+	const GValue *value, GParamSpec *pspec);
+static void ld_symbol_category_finalize (GObject *gobject);
+
+
+G_DEFINE_TYPE (LdSymbolCategory, ld_symbol_category, G_TYPE_OBJECT);
+
+static void
+ld_symbol_category_class_init (LdSymbolCategoryClass *klass)
+{
+	GObjectClass *object_class;
+	GParamSpec *pspec;
+
+	object_class = G_OBJECT_CLASS (klass);
+	object_class->get_property = ld_symbol_category_get_property;
+	object_class->set_property = ld_symbol_category_set_property;
+	object_class->finalize = ld_symbol_category_finalize;
+
+/**
+ * LdSymbolCategory:name:
+ *
+ * The name of this symbol category.
+ */
+	pspec = g_param_spec_string ("name", "Name",
+		"The name of this symbol category.",
+		"", G_PARAM_READWRITE);
+	g_object_class_install_property (object_class, PROP_NAME, pspec);
+
+/**
+ * LdSymbolCategory:human-name:
+ *
+ * The localized human name of this symbol category.
+ */
+	pspec = g_param_spec_string ("human-name", "Human name",
+		"The localized human name of this symbol category.",
+		"", G_PARAM_READWRITE);
+	g_object_class_install_property (object_class, PROP_HUMAN_NAME, pspec);
+
+/**
+ * LdSymbolCategory:image-path:
+ *
+ * Path to an image file representing this category.
+ */
+	pspec = g_param_spec_string ("image-path", "Image path",
+		"Path to an image file representing this category.",
+		"", G_PARAM_READWRITE);
+	g_object_class_install_property (object_class, PROP_IMAGE_PATH, pspec);
+
+	g_type_class_add_private (klass, sizeof (LdSymbolCategoryPrivate));
+}
+
+static void
+ld_symbol_category_init (LdSymbolCategory *self)
+{
+	self->priv = G_TYPE_INSTANCE_GET_PRIVATE
+		(self, LD_TYPE_SYMBOL_CATEGORY, LdSymbolCategoryPrivate);
+}
+
+static void
+ld_symbol_category_get_property (GObject *object, guint property_id,
+	GValue *value, GParamSpec *pspec)
+{
+	LdSymbolCategory *self;
+
+	self = LD_SYMBOL_CATEGORY (object);
+	switch (property_id)
+	{
+	case PROP_NAME:
+		g_value_set_string (value, ld_symbol_category_get_name (self));
+		break;
+	case PROP_HUMAN_NAME:
+		g_value_set_string (value, ld_symbol_category_get_human_name (self));
+		break;
+	case PROP_IMAGE_PATH:
+		g_value_set_string (value, ld_symbol_category_get_image_path (self));
+		break;
+	default:
+		G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
+	}
+}
+
+static void
+ld_symbol_category_set_property (GObject *object, guint property_id,
+	const GValue *value, GParamSpec *pspec)
+{
+	LdSymbolCategory *self;
+
+	self = LD_SYMBOL_CATEGORY (object);
+	switch (property_id)
+	{
+	case PROP_NAME:
+		ld_symbol_category_set_name (self, g_value_get_string (value));
+		break;
+	case PROP_HUMAN_NAME:
+		ld_symbol_category_set_human_name (self, g_value_get_string (value));
+		break;
+	case PROP_IMAGE_PATH:
+		ld_symbol_category_set_image_path (self, g_value_get_string (value));
+		break;
+	default:
+		G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
+	}
+}
+
+static void
+ld_symbol_category_finalize (GObject *gobject)
+{
+	LdSymbolCategory *self;
+
+	self = LD_SYMBOL_CATEGORY (gobject);
+
+	if (self->priv->name)
+		g_free (self->priv->name);
+	if (self->priv->human_name)
+		g_free (self->priv->human_name);
+	if (self->priv->image_path)
+		g_free (self->priv->image_path);
+
+	g_slist_foreach (self->priv->children, (GFunc) g_object_unref, NULL);
+	g_slist_free (self->priv->children);
+
+	/* Chain up to the parent class. */
+	G_OBJECT_CLASS (ld_symbol_category_parent_class)->finalize (gobject);
+}
+
+
+/**
+ * ld_symbol_category_new:
+ * @name: The name of the new category.
+ * @human_name: The localized human name of the new category.
+ *
+ * Create an instance.
+ */
+LdSymbolCategory *
+ld_symbol_category_new (const gchar *name, const gchar *human_name)
+{
+	LdSymbolCategory *cat;
+
+	g_return_val_if_fail (name != NULL, NULL);
+	g_return_val_if_fail (human_name != NULL, NULL);
+
+	cat = g_object_new (LD_TYPE_SYMBOL_CATEGORY, NULL);
+	cat->priv->name = g_strdup (name);
+	cat->priv->human_name = g_strdup (human_name);
+
+	return cat;
+}
+
+/**
+ * ld_symbol_category_set_name:
+ * @self: An #LdSymbolCategory object.
+ * @name: The new name for this category.
+ */
+void
+ld_symbol_category_set_name (LdSymbolCategory *self, const gchar *name)
+{
+	g_return_if_fail (LD_IS_SYMBOL_CATEGORY (self));
+	g_return_if_fail (name != NULL);
+
+	if (self->priv->name)
+		g_free (self->priv->name);
+	self->priv->name = g_strdup (name);
+
+	g_object_notify (G_OBJECT (self), "name");
+}
+
+/**
+ * ld_symbol_category_get_name:
+ * @self: An #LdSymbolCategory object.
+ *
+ * Return the name of this category.
+ */
+const gchar *
+ld_symbol_category_get_name (LdSymbolCategory *self)
+{
+	g_return_val_if_fail (LD_IS_SYMBOL_CATEGORY (self), NULL);
+	return self->priv->name;
+}
+
+/**
+ * ld_symbol_category_set_human_name:
+ * @self: An #LdSymbolCategory object.
+ * @human_name: The new localized human name for this category.
+ */
+void
+ld_symbol_category_set_human_name (LdSymbolCategory *self,
+	const gchar *human_name)
+{
+	g_return_if_fail (LD_IS_SYMBOL_CATEGORY (self));
+	g_return_if_fail (human_name != NULL);
+
+	if (self->priv->human_name)
+		g_free (self->priv->human_name);
+	self->priv->human_name = g_strdup (human_name);
+
+	g_object_notify (G_OBJECT (self), "human-name");
+}
+
+/**
+ * ld_symbol_category_get_human_name:
+ * @self: An #LdSymbolCategory object.
+ *
+ * Return the localized human name of this category.
+ */
+const gchar *
+ld_symbol_category_get_human_name (LdSymbolCategory *self)
+{
+	g_return_val_if_fail (LD_IS_SYMBOL_CATEGORY (self), NULL);
+	return self->priv->human_name;
+}
+
+/**
+ * ld_symbol_category_set_image_path:
+ * @self: An #LdSymbolCategory object.
+ * @image_path: The new path to the image for this category. May be NULL.
+ */
+void
+ld_symbol_category_set_image_path (LdSymbolCategory *self,
+	const gchar *image_path)
+{
+	g_return_if_fail (LD_IS_SYMBOL_CATEGORY (self));
+
+	if (self->priv->image_path)
+		g_free (self->priv->image_path);
+	self->priv->image_path = g_strdup (image_path);
+
+	g_object_notify (G_OBJECT (self), "image-path");
+}
+
+/**
+ * ld_symbol_category_get_image_path:
+ * @self: An #LdSymbolCategory object.
+ *
+ * Return the filesystem path to the image for this category. May be NULL.
+ */
+const gchar *
+ld_symbol_category_get_image_path (LdSymbolCategory *self)
+{
+	g_return_val_if_fail (LD_IS_SYMBOL_CATEGORY (self), NULL);
+	return self->priv->image_path;
+}
+
+/**
+ * ld_symbol_category_insert_child:
+ * @self: An #LdSymbolCategory object.
+ * @child: The child to be inserted.
+ * @pos: The position at which the child will be inserted.
+ *       Negative values will append to the end of list.
+ *
+ * Insert a child into the category.
+ */
+void
+ld_symbol_category_insert_child (LdSymbolCategory *self,
+	GObject *child, gint pos)
+{
+	g_return_if_fail (LD_IS_SYMBOL_CATEGORY (self));
+	g_return_if_fail (G_IS_OBJECT (child));
+
+	g_object_ref (child);
+	self->priv->children = g_slist_insert (self->priv->children, child, pos);
+}
+
+/**
+ * ld_symbol_category_remove_child:
+ * @self: An #LdSymbolCategory object.
+ * @child: The child to be removed.
+ *
+ * Removes a child from the category.
+ */
+void
+ld_symbol_category_remove_child (LdSymbolCategory *self,
+	GObject *child)
+{
+	g_return_if_fail (LD_IS_SYMBOL_CATEGORY (self));
+	g_return_if_fail (G_IS_OBJECT (child));
+
+	g_object_unref (child);
+	self->priv->children = g_slist_remove (self->priv->children, child);
+}
+
+/**
+ * ld_symbol_category_get_children:
+ * @self: An #LdSymbolCategory object.
+ *
+ * Return value: The internal list of children. Do not modify.
+ */
+const GSList *
+ld_symbol_category_get_children (LdSymbolCategory *self)
+{
+	g_return_val_if_fail (LD_IS_SYMBOL_CATEGORY (self), NULL);
+	return self->priv->children;
+}
+
diff --git a/liblogdiag/ld-symbol-category.h b/liblogdiag/ld-symbol-category.h
new file mode 100644
index 0000000..3b1f05b
--- /dev/null
+++ b/liblogdiag/ld-symbol-category.h
@@ -0,0 +1,79 @@
+/*
+ * ld-symbol-category.h
+ *
+ * This file is a part of logdiag.
+ * Copyright Přemysl Janouch 2010. All rights reserved.
+ *
+ * See the file LICENSE for licensing information.
+ *
+ */
+
+#ifndef __LD_SYMBOL_CATEGORY_H__
+#define __LD_SYMBOL_CATEGORY_H__
+
+G_BEGIN_DECLS
+
+
+#define LD_TYPE_SYMBOL_CATEGORY (ld_symbol_category_get_type ())
+#define LD_SYMBOL_CATEGORY(obj) (G_TYPE_CHECK_INSTANCE_CAST \
+	((obj), LD_TYPE_SYMBOL_CATEGORY, LdSymbolCategory))
+#define LD_SYMBOL_CATEGORY_CLASS(klass) (G_TYPE_CHECK_CLASS_CAST \
+	((klass), LD_TYPE_SYMBOL_CATEGORY, LdSymbolCategoryClass))
+#define LD_IS_SYMBOL_CATEGORY(obj) (G_TYPE_CHECK_INSTANCE_TYPE \
+	((obj), LD_TYPE_SYMBOL_CATEGORY))
+#define LD_IS_SYMBOL_CATEGORY_CLASS(klass) (G_TYPE_CHECK_INSTANCE_TYPE \
+	((klass), LD_TYPE_SYMBOL_CATEGORY))
+#define LD_SYMBOL_CATEGORY_GET_CLASS(obj) (G_TYPE_INSTANCE_GET_CLASS \
+	((obj), LD_SYMBOL_CATEGORY, LdSymbolCategoryClass))
+
+typedef struct _LdSymbolCategory LdSymbolCategory;
+typedef struct _LdSymbolCategoryPrivate LdSymbolCategoryPrivate;
+typedef struct _LdSymbolCategoryClass LdSymbolCategoryClass;
+
+
+/**
+ * LdSymbolCategory:
+ */
+struct _LdSymbolCategory
+{
+/*< private >*/
+	GObject parent_instance;
+	LdSymbolCategoryPrivate *priv;
+};
+
+/* TODO: If required sometime, categories (and maybe symbols) should implement
+ *       a "changed" signal. This can be somewhat tricky. The library might be
+ *       a good candidate for what they call a proxy. See GtkUIManager.
+ */
+struct _LdSymbolCategoryClass
+{
+/*< private >*/
+	GObjectClass parent_class;
+};
+
+
+GType ld_symbol_category_get_type (void) G_GNUC_CONST;
+
+LdSymbolCategory *ld_symbol_category_new (const gchar *name,
+	const gchar *human_name);
+
+void ld_symbol_category_set_name (LdSymbolCategory *self, const gchar *name);
+const gchar *ld_symbol_category_get_name (LdSymbolCategory *self);
+void ld_symbol_category_set_human_name (LdSymbolCategory *self,
+	const gchar *human_name);
+const gchar *ld_symbol_category_get_human_name (LdSymbolCategory *self);
+void ld_symbol_category_set_image_path (LdSymbolCategory *self,
+	const gchar *image_path);
+const gchar *ld_symbol_category_get_image_path (LdSymbolCategory *self);
+
+void ld_symbol_category_insert_child (LdSymbolCategory *self,
+	GObject *child, gint pos);
+void ld_symbol_category_remove_child (LdSymbolCategory *self,
+	GObject *child);
+const GSList *ld_symbol_category_get_children (LdSymbolCategory *self);
+
+
+G_END_DECLS
+
+#endif /* ! __LD_SYMBOL_CATEGORY_H__ */
+
diff --git a/liblogdiag/ld-symbol.c b/liblogdiag/ld-symbol.c
new file mode 100644
index 0000000..fafa9ab
--- /dev/null
+++ b/liblogdiag/ld-symbol.c
@@ -0,0 +1,232 @@
+/*
+ * ld-symbol.c
+ *
+ * This file is a part of logdiag.
+ * Copyright Přemysl Janouch 2010 - 2011. All rights reserved.
+ *
+ * See the file LICENSE for licensing information.
+ *
+ */
+
+#include "liblogdiag.h"
+#include "config.h"
+
+
+/**
+ * SECTION:ld-symbol
+ * @short_description: A symbol.
+ * @see_also: #LdDiagramSymbol, #LdCanvas
+ *
+ * #LdSymbol represents a symbol to be drawn onto a #LdCanvas.
+ *
+ * All implementations of this abstract class are required to use
+ * cairo_save() and cairo_restore() when drawing to store the state.
+ */
+
+enum
+{
+	PROP_0,
+	PROP_NAME,
+	PROP_HUMAN_NAME,
+	PROP_AREA,
+	PROP_TERMINALS
+};
+
+static void ld_symbol_get_property (GObject *object, guint property_id,
+	GValue *value, GParamSpec *pspec);
+static void ld_symbol_set_property (GObject *object, guint property_id,
+	const GValue *value, GParamSpec *pspec);
+
+
+G_DEFINE_ABSTRACT_TYPE (LdSymbol, ld_symbol, G_TYPE_OBJECT);
+
+static void
+ld_symbol_class_init (LdSymbolClass *klass)
+{
+	GObjectClass *object_class;
+	GParamSpec *pspec;
+
+	object_class = G_OBJECT_CLASS (klass);
+	object_class->get_property = ld_symbol_get_property;
+	object_class->set_property = ld_symbol_set_property;
+
+/**
+ * LdSymbol:name:
+ *
+ * The name of this symbol.
+ */
+	pspec = g_param_spec_string ("name", "Name",
+		"The name of this symbol.",
+		"", G_PARAM_READABLE);
+	g_object_class_install_property (object_class, PROP_NAME, pspec);
+
+/**
+ * LdSymbol:human-name:
+ *
+ * The localized human name of this symbol.
+ */
+	pspec = g_param_spec_string ("human-name", "Human name",
+		"The localized human name of this symbol.",
+		"", G_PARAM_READABLE);
+	g_object_class_install_property (object_class, PROP_HUMAN_NAME, pspec);
+
+/**
+ * LdSymbol:area:
+ *
+ * The area of this symbol.
+ */
+	pspec = g_param_spec_boxed ("area", "Area",
+		"The area of this symbol.",
+		LD_TYPE_RECTANGLE, G_PARAM_READABLE);
+	g_object_class_install_property (object_class, PROP_AREA, pspec);
+
+/**
+ * LdSymbol:terminals:
+ *
+ * A point array that specifies terminals of this symbol.
+ */
+	pspec = g_param_spec_boxed ("terminals", "Terminals",
+		"A point array that specifies terminals of this symbol.",
+		LD_TYPE_POINT_ARRAY, G_PARAM_READABLE);
+	g_object_class_install_property (object_class, PROP_TERMINALS, pspec);
+}
+
+static void
+ld_symbol_init (LdSymbol *self)
+{
+}
+
+static void
+ld_symbol_get_property (GObject *object, guint property_id,
+	GValue *value, GParamSpec *pspec)
+{
+	LdSymbol *self;
+
+	self = LD_SYMBOL (object);
+	switch (property_id)
+	{
+	case PROP_NAME:
+		g_value_set_string (value, ld_symbol_get_name (self));
+		break;
+	case PROP_HUMAN_NAME:
+		g_value_set_string (value, ld_symbol_get_human_name (self));
+		break;
+	case PROP_AREA:
+		{
+			LdRectangle area;
+
+			ld_symbol_get_area (self, &area);
+			g_value_set_boxed (value, &area);
+		}
+		break;
+	case PROP_TERMINALS:
+		g_value_set_boxed (value, ld_symbol_get_terminals (self));
+		break;
+	default:
+		G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
+	}
+}
+
+static void
+ld_symbol_set_property (GObject *object, guint property_id,
+	const GValue *value, GParamSpec *pspec)
+{
+	G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
+}
+
+
+/**
+ * ld_symbol_get_name:
+ * @self: An #LdSymbol object.
+ *
+ * Return value: The name of the symbol.
+ */
+const gchar *
+ld_symbol_get_name (LdSymbol *self)
+{
+	LdSymbolClass *klass;
+
+	g_return_val_if_fail (LD_IS_SYMBOL (self), NULL);
+
+	klass = LD_SYMBOL_GET_CLASS (self);
+	g_return_val_if_fail (klass->get_name != NULL, NULL);
+	return klass->get_name (self);
+}
+
+/**
+ * ld_symbol_get_human_name:
+ * @self: An #LdSymbol object.
+ *
+ * Return value: The localised human name of the symbol.
+ */
+const gchar *
+ld_symbol_get_human_name (LdSymbol *self)
+{
+	LdSymbolClass *klass;
+
+	g_return_val_if_fail (LD_IS_SYMBOL (self), NULL);
+
+	klass = LD_SYMBOL_GET_CLASS (self);
+	g_return_val_if_fail (klass->get_human_name != NULL, NULL);
+	return klass->get_human_name (self);
+}
+
+/**
+ * ld_symbol_get_area:
+ * @self: An #LdSymbol object.
+ * @area: Where the area of the symbol will be returned.
+ *
+ * Get the area of the symbol.
+ */
+void
+ld_symbol_get_area (LdSymbol *self, LdRectangle *area)
+{
+	LdSymbolClass *klass;
+
+	g_return_if_fail (LD_IS_SYMBOL (self));
+	g_return_if_fail (area != NULL);
+
+	klass = LD_SYMBOL_GET_CLASS (self);
+	g_return_if_fail (klass->get_area != NULL);
+	klass->get_area (self, area);
+}
+
+/**
+ * ld_symbol_get_terminals:
+ * @self: An #LdSymbol object.
+ *
+ * Get a list of symbol terminals.
+ *
+ * Return value: An #LdPointArray structure.
+ */
+const LdPointArray *
+ld_symbol_get_terminals (LdSymbol *self)
+{
+	LdSymbolClass *klass;
+
+	g_return_val_if_fail (LD_IS_SYMBOL (self), NULL);
+
+	klass = LD_SYMBOL_GET_CLASS (self);
+	g_return_val_if_fail (klass->get_terminals != NULL, NULL);
+	return klass->get_terminals (self);
+}
+
+/**
+ * ld_symbol_draw:
+ * @self: An #LdSymbol object.
+ * @cr: A cairo surface to be drawn on.
+ *
+ * Draw the symbol onto a Cairo surface.
+ */
+void
+ld_symbol_draw (LdSymbol *self, cairo_t *cr)
+{
+	LdSymbolClass *klass;
+
+	g_return_if_fail (LD_IS_SYMBOL (self));
+	g_return_if_fail (cr != NULL);
+
+	klass = LD_SYMBOL_GET_CLASS (self);
+	g_return_if_fail (klass->draw != NULL);
+	klass->draw (self, cr);
+}
diff --git a/liblogdiag/ld-symbol.h b/liblogdiag/ld-symbol.h
new file mode 100644
index 0000000..409eba5
--- /dev/null
+++ b/liblogdiag/ld-symbol.h
@@ -0,0 +1,74 @@
+/*
+ * ld-symbol.h
+ *
+ * This file is a part of logdiag.
+ * Copyright Přemysl Janouch 2010 - 2011. All rights reserved.
+ *
+ * See the file LICENSE for licensing information.
+ *
+ */
+
+#ifndef __LD_SYMBOL_H__
+#define __LD_SYMBOL_H__
+
+G_BEGIN_DECLS
+
+
+#define LD_TYPE_SYMBOL (ld_symbol_get_type ())
+#define LD_SYMBOL(obj) (G_TYPE_CHECK_INSTANCE_CAST \
+	((obj), LD_TYPE_SYMBOL, LdSymbol))
+#define LD_SYMBOL_CLASS(klass) (G_TYPE_CHECK_CLASS_CAST \
+	((klass), LD_TYPE_SYMBOL, LdSymbolClass))
+#define LD_IS_SYMBOL(obj) (G_TYPE_CHECK_INSTANCE_TYPE \
+	((obj), LD_TYPE_SYMBOL))
+#define LD_IS_SYMBOL_CLASS(klass) (G_TYPE_CHECK_INSTANCE_TYPE \
+	((klass), LD_TYPE_SYMBOL))
+#define LD_SYMBOL_GET_CLASS(obj) (G_TYPE_INSTANCE_GET_CLASS \
+	((obj), LD_SYMBOL, LdSymbolClass))
+
+typedef struct _LdSymbol LdSymbol;
+typedef struct _LdSymbolPrivate LdSymbolPrivate;
+typedef struct _LdSymbolClass LdSymbolClass;
+
+
+struct _LdSymbol
+{
+/*< private >*/
+	GObject parent_instance;
+	LdSymbolPrivate *priv;
+};
+
+/**
+ * LdSymbolClass:
+ * @parent_class: The parent class.
+ * @get_name: Get the name of the symbol.
+ * @get_human_name: Get the localized human name of the symbol.
+ * @get_area: Get the area of the symbol.
+ * @get_terminals: Get a list of symbol terminals.
+ * @draw: Draw the symbol on a Cairo surface.
+ */
+struct _LdSymbolClass
+{
+	GObjectClass parent_class;
+
+	const gchar *(*get_name) (LdSymbol *self);
+	const gchar *(*get_human_name) (LdSymbol *self);
+	void (*get_area) (LdSymbol *self, LdRectangle *area);
+	const LdPointArray *(*get_terminals) (LdSymbol *self);
+	void (*draw) (LdSymbol *self, cairo_t *cr);
+};
+
+
+GType ld_symbol_get_type (void) G_GNUC_CONST;
+
+const gchar *ld_symbol_get_name (LdSymbol *self);
+const gchar *ld_symbol_get_human_name (LdSymbol *self);
+void ld_symbol_get_area (LdSymbol *self, LdRectangle *area);
+const LdPointArray *ld_symbol_get_terminals (LdSymbol *self);
+void ld_symbol_draw (LdSymbol *self, cairo_t *cr);
+
+
+G_END_DECLS
+
+#endif /* ! __LD_SYMBOL_H__ */
+
diff --git a/liblogdiag/ld-types.c b/liblogdiag/ld-types.c
new file mode 100644
index 0000000..cde3da6
--- /dev/null
+++ b/liblogdiag/ld-types.c
@@ -0,0 +1,221 @@
+/*
+ * ld-types.c
+ *
+ * This file is a part of logdiag.
+ * Copyright Přemysl Janouch 2010 - 2011. All rights reserved.
+ *
+ * See the file LICENSE for licensing information.
+ *
+ */
+
+#include <math.h>
+
+#include "liblogdiag.h"
+#include "config.h"
+
+
+#define DEFINE_BOXED_TYPE(TypeName, type_name) \
+GType \
+type_name ## _get_type (void) \
+{ \
+	static GType our_type = 0; \
+	if (our_type == 0) \
+		our_type = g_boxed_type_register_static \
+			(g_intern_static_string (#TypeName), \
+			(GBoxedCopyFunc) type_name ## _copy, \
+			(GBoxedFreeFunc) type_name ## _free); \
+	return our_type; \
+}
+
+DEFINE_BOXED_TYPE (LdPoint, ld_point)
+DEFINE_BOXED_TYPE (LdPointArray, ld_point_array)
+DEFINE_BOXED_TYPE (LdRectangle, ld_rectangle)
+
+#define DEFINE_BOXED_TRIVIAL_COPY(TypeName, type_name) \
+TypeName * \
+type_name ## _copy (const TypeName *self) \
+{ \
+	TypeName *new_copy; \
+	g_return_val_if_fail (self != NULL, NULL); \
+	new_copy = g_slice_new (TypeName); \
+	*new_copy = *self; \
+	return new_copy; \
+}
+
+#define DEFINE_BOXED_TRIVIAL_FREE(TypeName, type_name) \
+void \
+type_name ## _free (TypeName *self) \
+{ \
+	g_return_if_fail (self != NULL); \
+	g_slice_free (TypeName, self); \
+}
+
+/**
+ * ld_point_copy:
+ * @self: An #LdPoint structure.
+ *
+ * Makes a copy of the structure.
+ * The result must be freed by ld_point_free().
+ *
+ * Return value: A copy of @self.
+ */
+DEFINE_BOXED_TRIVIAL_COPY (LdPoint, ld_point)
+
+/**
+ * ld_point_free:
+ * @self: An #LdPoint structure.
+ *
+ * Frees the structure created with ld_point_copy().
+ */
+DEFINE_BOXED_TRIVIAL_FREE (LdPoint, ld_point)
+
+/**
+ * ld_point_distance:
+ * @self: An #LdPoint structure.
+ * @x: The X coordinate of the second point.
+ * @y: The Y coordinate of the second point.
+ *
+ * Compute the distance between two points.
+ */
+gdouble
+ld_point_distance (LdPoint *self, gdouble x, gdouble y)
+{
+	gdouble dx, dy;
+
+	g_return_val_if_fail (self != NULL, -1);
+
+	dx = self->x - x;
+	dy = self->y - y;
+	return sqrt (dx * dx + dy * dy);
+}
+
+/**
+ * ld_point_array_new:
+ * @num_points: The number of points the array can store.
+ *
+ * Create a new array of points and initialize.
+ *
+ * Return value: An #LdPointArray structure.
+ */
+LdPointArray *
+ld_point_array_new (gint num_points)
+{
+	LdPointArray *new_array;
+
+	g_return_val_if_fail (num_points >= 1, NULL);
+
+	new_array = g_slice_new (LdPointArray);
+	new_array->num_points = num_points;
+	new_array->points = g_malloc0 (num_points * sizeof (LdPoint));
+	return new_array;
+}
+
+/**
+ * ld_point_array_copy:
+ * @self: An #LdPointArray structure.
+ *
+ * Makes a copy of the structure.
+ * The result must be freed by ld_point_array_free().
+ *
+ * Return value: A copy of @self.
+ */
+LdPointArray *
+ld_point_array_copy (const LdPointArray *self)
+{
+	LdPointArray *new_array;
+
+	g_return_val_if_fail (self != NULL, NULL);
+
+	new_array = g_slice_new (LdPointArray);
+	new_array->num_points = self->num_points;
+	new_array->points = g_memdup (self->points,
+		self->num_points * sizeof (LdPoint));
+	return new_array;
+}
+
+/**
+ * ld_point_array_free:
+ * @self: An #LdPointArray structure.
+ *
+ * Frees the structure created with ld_point_array_copy().
+ */
+void
+ld_point_array_free (LdPointArray *self)
+{
+	g_return_if_fail (self != NULL);
+
+	g_free (self->points);
+	g_slice_free (LdPointArray, self);
+}
+
+/**
+ * ld_rectangle_copy:
+ * @self: An #LdRectangle structure.
+ *
+ * Makes a copy of the structure.
+ * The result must be freed by ld_rectangle_free().
+ *
+ * Return value: A copy of @self.
+ */
+DEFINE_BOXED_TRIVIAL_COPY (LdRectangle, ld_rectangle)
+
+/**
+ * ld_rectangle_free:
+ * @self: An #LdRectangle structure.
+ *
+ * Frees the structure created with ld_rectangle_copy().
+ */
+DEFINE_BOXED_TRIVIAL_FREE (LdRectangle, ld_rectangle)
+
+/**
+ * ld_rectangle_contains:
+ * @self: An #LdRectangle structure.
+ * @x: The X coordinate of the point to be checked.
+ * @y: The Y coordinate of the point to be checked.
+ *
+ * Return value: TRUE if the rectangle contains the specified point.
+ */
+gboolean
+ld_rectangle_contains (LdRectangle *self, gdouble x, gdouble y)
+{
+	g_return_val_if_fail (self != NULL, FALSE);
+	return (x >= self->x && x <= self->x + self->width
+	     && y >= self->y && y <= self->y + self->height);
+}
+
+/**
+ * ld_rectangle_intersects:
+ * @self: An #LdRectangle structure.
+ * @rect: An #LdRectangle to be checked for intersection.
+ *
+ * Return value: TRUE if the two rectangles intersect.
+ */
+gboolean
+ld_rectangle_intersects (LdRectangle *self, LdRectangle *rect)
+{
+	g_return_val_if_fail (self != NULL, FALSE);
+	g_return_val_if_fail (rect != NULL, FALSE);
+
+	return !(self->x > rect->x + rect->width
+	      || self->y > rect->y + rect->height
+	      || self->x + self->width  < rect->x
+	      || self->y + self->height < rect->y);
+}
+
+/**
+ * ld_rectangle_extend:
+ * @self: An #LdRectangle structure.
+ * @border: The border by which the rectangle should be extended.
+ *
+ * Extend a rectangle on all sides.
+ */
+void
+ld_rectangle_extend (LdRectangle *self, gdouble border)
+{
+	g_return_if_fail (self != NULL);
+
+	self->x -= border;
+	self->y -= border;
+	self->width  += 2 * border;
+	self->height += 2 * border;
+}
diff --git a/liblogdiag/ld-types.h b/liblogdiag/ld-types.h
new file mode 100644
index 0000000..61a1a7d
--- /dev/null
+++ b/liblogdiag/ld-types.h
@@ -0,0 +1,101 @@
+/*
+ * ld-types.h
+ *
+ * This file is a part of logdiag.
+ * Copyright Přemysl Janouch 2010 - 2011. All rights reserved.
+ *
+ * See the file LICENSE for licensing information.
+ *
+ */
+
+#ifndef __LD_TYPES_H__
+#define __LD_TYPES_H__
+
+G_BEGIN_DECLS
+
+
+/**
+ * SECTION:ld-types
+ * @short_description: Simple data types.
+ *
+ * #LdPoint defines coordinates of a point.
+ *
+ * #LdRectangle defines the position and size of a rectangle.
+ */
+
+#define LD_TYPE_POINT (ld_point_get_type ())
+#define LD_TYPE_POINT_ARRAY (ld_point_array_get_type ())
+#define LD_TYPE_RECTANGLE (ld_rectangle_get_type ())
+
+typedef struct _LdPoint LdPoint;
+typedef struct _LdPointArray LdPointArray;
+typedef struct _LdRectangle LdRectangle;
+
+
+/**
+ * LdPoint:
+ * @x: The X coordinate.
+ * @y: The Y coordinate.
+ *
+ * Defines a point.
+ */
+struct _LdPoint
+{
+	gdouble x, y;
+};
+
+GType ld_point_get_type (void) G_GNUC_CONST;
+
+LdPoint *ld_point_copy (const LdPoint *self);
+void ld_point_free (LdPoint *self);
+gdouble ld_point_distance (LdPoint *self, gdouble x, gdouble y);
+
+
+/**
+ * LdPointArray:
+ * @points: An array of #LdPoint structures.
+ * @num_points: Count of points in @points.
+ *
+ * Moves quickly.
+ */
+struct _LdPointArray
+{
+	LdPoint *points;
+	gint num_points;
+};
+
+GType ld_point_array_get_type (void) G_GNUC_CONST;
+
+LdPointArray *ld_point_array_new (gint num_points);
+LdPointArray *ld_point_array_copy (const LdPointArray *self);
+void ld_point_array_free (LdPointArray *self);
+
+
+/**
+ * LdRectangle:
+ * @x: Left-top X coordinate.
+ * @y: Left-top Y coordinate.
+ * @width: Width of the area, must be positive.
+ * @height: Height of the area, must be positive.
+ *
+ * Defines a rectangle.
+ */
+struct _LdRectangle
+{
+	gdouble x, y;
+	gdouble width, height;
+};
+
+GType ld_rectangle_get_type (void) G_GNUC_CONST;
+
+LdRectangle *ld_rectangle_copy (const LdRectangle *self);
+void ld_rectangle_free (LdRectangle *self);
+gboolean ld_rectangle_contains (LdRectangle *self, gdouble x, gdouble y);
+gboolean ld_rectangle_intersects (LdRectangle *self, LdRectangle *rect);
+void ld_rectangle_extend (LdRectangle *self, gdouble border);
+
+
+G_END_DECLS
+
+#endif /* ! __LD_TYPES_H__ */
+
diff --git a/liblogdiag/liblogdiag.h b/liblogdiag/liblogdiag.h
new file mode 100644
index 0000000..800826f
--- /dev/null
+++ b/liblogdiag/liblogdiag.h
@@ -0,0 +1,34 @@
+/*
+ * liblogdiag.h
+ *
+ * This file is a part of logdiag.
+ * Copyright Přemysl Janouch 2011. All rights reserved.
+ *
+ * See the file LICENSE for licensing information.
+ *
+ */
+
+#ifndef __LIBLOGDIAG_H__
+#define __LIBLOGDIAG_H__
+
+#include <gtk/gtk.h>
+#include <json-glib/json-glib.h>
+
+#include "ld-marshal.h"
+#include "ld-types.h"
+
+#include "ld-symbol.h"
+#include "ld-symbol-category.h"
+#include "ld-library.h"
+
+#include "ld-diagram-object.h"
+#include "ld-diagram-symbol.h"
+#include "ld-diagram.h"
+
+#include "ld-canvas.h"
+
+#include "ld-lua.h"
+#include "ld-lua-symbol.h"
+
+#endif /* ! __LIBLOGDIAG_H__ */
+