Rename LdCanvas to LdDiagramView.

1 files changed, 2346 insertions, 0 deletions

diff --git a/liblogdiag/ld-diagram-view.c b/liblogdiag/ld-diagram-view.c
new file mode 100644
index 0000000..5991824
--- /dev/null
+++ b/liblogdiag/ld-diagram-view.c
@@ -0,0 +1,2346 @@
+/*
+ * ld-diagram-view.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-diagram-view
+ * @short_description: A widget that displays an LdDiagram
+ * @see_also: #LdDiagram
+ *
+ * #LdDiagramView 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. */
+#define ZOOM_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) (LdDiagramView *self);
+
+enum
+{
+	OPER_0,
+	OPER_ADD_OBJECT,
+	OPER_CONNECT,
+	OPER_SELECT,
+	OPER_MOVE_SELECTION
+};
+
+typedef struct _AddObjectData AddObjectData;
+typedef struct _ConnectData ConnectData;
+typedef struct _SelectData SelectData;
+typedef struct _MoveSelectionData MoveSelectionData;
+
+struct _AddObjectData
+{
+	LdDiagramObject *object;
+	gboolean visible;
+};
+
+struct _ConnectData
+{
+	LdDiagramConnection *connection;
+	LdPoint origin;
+};
+
+struct _SelectData
+{
+	LdPoint drag_last_pos;
+};
+
+struct _MoveSelectionData
+{
+	LdPoint move_origin;
+};
+
+enum
+{
+	COLOR_BASE,
+	COLOR_GRID,
+	COLOR_OBJECT,
+	COLOR_SELECTION,
+	COLOR_TERMINAL,
+	COLOR_COUNT
+};
+
+typedef struct _Color Color;
+
+struct _Color
+{
+	gdouble r;
+	gdouble g;
+	gdouble b;
+	gdouble a;
+};
+
+/*
+ * LdDiagramViewPrivate:
+ * @diagram: a diagram object assigned as a model.
+ * @library: a library object assigned 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.
+ * @terminal: position of the highlighted terminal.
+ * @terminal_hovered: whether a terminal is hovered.
+ * @drag_start_pos: position of the mouse pointer when dragging started.
+ * @drag_operation: the operation to start when dragging starts.
+ * @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 _LdDiagramViewPrivate
+{
+	LdDiagram *diagram;
+	LdLibrary *library;
+
+	GtkAdjustment *adjustment_h;
+	GtkAdjustment *adjustment_v;
+
+	gdouble x;
+	gdouble y;
+	gdouble zoom;
+
+	LdPoint terminal;
+	gboolean terminal_hovered;
+
+	LdPoint drag_start_pos;
+	gint drag_operation;
+
+	gint operation;
+	union
+	{
+		AddObjectData add_object;
+		ConnectData connect;
+		SelectData select;
+		MoveSelectionData move_selection;
+	}
+	operation_data;
+	OperationEnd operation_end;
+
+	Color 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 #LdDiagramView.
+ * @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
+{
+	LdDiagramView *self;
+	cairo_t *cr;
+	LdRectangle exposed_rect;
+	gdouble scale;
+};
+
+enum
+{
+	PROP_0,
+	PROP_DIAGRAM,
+	PROP_LIBRARY,
+	PROP_ZOOM
+};
+
+static void ld_diagram_view_get_property (GObject *object, guint property_id,
+	GValue *value, GParamSpec *pspec);
+static void ld_diagram_view_set_property (GObject *object, guint property_id,
+	const GValue *value, GParamSpec *pspec);
+static void ld_diagram_view_finalize (GObject *gobject);
+
+static void ld_diagram_view_real_set_scroll_adjustments
+	(LdDiagramView *self, GtkAdjustment *horizontal, GtkAdjustment *vertical);
+static void on_adjustment_value_changed
+	(GtkAdjustment *adjustment, LdDiagramView *self);
+static void on_size_allocate (GtkWidget *widget, GtkAllocation *allocation,
+	gpointer user_data);
+static void update_adjustments (LdDiagramView *self);
+static void ld_diagram_view_real_move (LdDiagramView *self,
+	gdouble dx, gdouble dy);
+
+static void diagram_connect_signals (LdDiagramView *self);
+static void diagram_disconnect_signals (LdDiagramView *self);
+
+static gdouble ld_diagram_view_get_base_unit_in_px (GtkWidget *self);
+static gdouble ld_diagram_view_get_scale_in_px (LdDiagramView *self);
+
+/* Helper functions. */
+static void color_set (Color *color,
+	gdouble r, gdouble g, gdouble b, gdouble a);
+static void color_apply (Color *color, cairo_t *cr);
+static guint32 color_to_cairo_argb (Color *color);
+
+static gdouble point_to_line_segment_distance
+	(const LdPoint *point, const LdPoint *p1, const LdPoint *p2);
+
+/* Generic functions. */
+static gboolean object_hit_test (LdDiagramView *self,
+	LdDiagramObject *object, const LdPoint *point);
+static gboolean get_object_clip_area (LdDiagramView *self,
+	LdDiagramObject *object, LdRectangle *rect);
+
+static void move_object_to_point (LdDiagramView *self, LdDiagramObject *object,
+	const LdPoint *point);
+static LdDiagramObject *get_object_at_point (LdDiagramView *self,
+	const LdPoint *point);
+
+static void move_selection (LdDiagramView *self, gdouble dx, gdouble dy);
+static gboolean is_object_selected (LdDiagramView *self,
+	LdDiagramObject *object);
+
+static void queue_draw (LdDiagramView *self, LdRectangle *rect);
+static void queue_object_draw (LdDiagramView *self, LdDiagramObject *object);
+
+/* Symbol terminals. */
+static void check_terminals (LdDiagramView *self, const LdPoint *point);
+static void rotate_terminal (LdPoint *terminal, gint symbol_rotation);
+static void hide_terminals (LdDiagramView *self);
+static void queue_terminal_draw (LdDiagramView *self, LdPoint *terminal);
+
+/* Diagram symbol. */
+static gboolean symbol_hit_test (LdDiagramView *self,
+	LdDiagramSymbol *symbol, const LdPoint *point);
+static gboolean get_symbol_clip_area (LdDiagramView *self,
+	LdDiagramSymbol *symbol, LdRectangle *rect);
+
+static gboolean get_symbol_area (LdDiagramView *self,
+	LdDiagramSymbol *symbol, LdRectangle *rect);
+static void rotate_symbol_area (LdRectangle *area, gint rotation);
+static void rotate_symbol (LdDiagramView *self, LdDiagramSymbol *symbol);
+static LdSymbol *resolve_symbol (LdDiagramView *self,
+	LdDiagramSymbol *diagram_symbol);
+
+/* Diagram connection. */
+static gboolean connection_hit_test (LdDiagramView *self,
+	LdDiagramConnection *connection, const LdPoint *point);
+static gboolean get_connection_clip_area (LdDiagramView *self,
+	LdDiagramConnection *connection, LdRectangle *rect);
+
+static gboolean get_connection_area (LdDiagramView *self,
+	LdDiagramConnection *connection, LdRectangle *rect);
+
+/* Operations. */
+static void ld_diagram_view_real_cancel_operation (LdDiagramView *self);
+static void oper_add_object_end (LdDiagramView *self);
+
+static void oper_connect_begin (LdDiagramView *self, const LdPoint *point);
+static void oper_connect_end (LdDiagramView *self);
+static void oper_connect_motion (LdDiagramView *self, const LdPoint *point);
+
+static void oper_select_begin (LdDiagramView *self, const LdPoint *point);
+static void oper_select_end (LdDiagramView *self);
+static void oper_select_get_rectangle (LdDiagramView *self, LdRectangle *rect);
+static void oper_select_queue_draw (LdDiagramView *self);
+static void oper_select_draw (GtkWidget *widget, DrawData *data);
+static void oper_select_motion (LdDiagramView *self, const LdPoint *point);
+
+static void oper_move_selection_begin (LdDiagramView *self,
+	const LdPoint *point);
+static void oper_move_selection_end (LdDiagramView *self);
+static void oper_move_selection_motion (LdDiagramView *self,
+	const LdPoint *point);
+
+/* Events, rendering. */
+static void simulate_motion (LdDiagramView *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 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);
+static void draw_connection (LdDiagramConnection *connection, DrawData *data);
+
+
+G_DEFINE_TYPE (LdDiagramView, ld_diagram_view, GTK_TYPE_DRAWING_AREA);
+
+static void
+ld_diagram_view_class_init (LdDiagramViewClass *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_diagram_view_get_property;
+	object_class->set_property = ld_diagram_view_set_property;
+	object_class->finalize = ld_diagram_view_finalize;
+
+	klass->set_scroll_adjustments = ld_diagram_view_real_set_scroll_adjustments;
+	klass->cancel_operation = ld_diagram_view_real_cancel_operation;
+	klass->move = ld_diagram_view_real_move;
+
+	binding_set = gtk_binding_set_by_class (klass);
+	gtk_binding_entry_add_signal (binding_set, GDK_Escape, 0,
+		"cancel-operation", 0);
+	gtk_binding_entry_add_signal (binding_set, GDK_Left, 0,
+		"move", 2, G_TYPE_DOUBLE, (gdouble) -1, G_TYPE_DOUBLE, (gdouble) 0);
+	gtk_binding_entry_add_signal (binding_set, GDK_Right, 0,
+		"move", 2, G_TYPE_DOUBLE, (gdouble) 1, G_TYPE_DOUBLE, (gdouble) 0);
+	gtk_binding_entry_add_signal (binding_set, GDK_Up, 0,
+		"move", 2, G_TYPE_DOUBLE, (gdouble) 0, G_TYPE_DOUBLE, (gdouble) -1);
+	gtk_binding_entry_add_signal (binding_set, GDK_Down, 0,
+		"move", 2, G_TYPE_DOUBLE, (gdouble) 0, G_TYPE_DOUBLE, (gdouble) 1);
+
+/**
+ * LdDiagramView:diagram:
+ *
+ * The underlying #LdDiagram object of this view.
+ */
+	pspec = g_param_spec_object ("diagram", "Diagram",
+		"The underlying diagram object of this view.",
+		LD_TYPE_DIAGRAM, G_PARAM_READWRITE);
+	g_object_class_install_property (object_class, PROP_DIAGRAM, pspec);
+
+/**
+ * LdDiagramView:library:
+ *
+ * The #LdLibrary from which symbols are retrieved.
+ */
+	pspec = g_param_spec_object ("library", "Library",
+		"The library from which symbols are retrieved.",
+		LD_TYPE_LIBRARY, G_PARAM_READWRITE);
+	g_object_class_install_property (object_class, PROP_LIBRARY, pspec);
+
+/**
+ * LdDiagramView:zoom:
+ *
+ * The zoom of this view.
+ */
+	pspec = g_param_spec_double ("zoom", "Zoom",
+		"The zoom of this view.",
+		ZOOM_MIN, ZOOM_MAX, ZOOM_DEFAULT, G_PARAM_READWRITE);
+	g_object_class_install_property (object_class, PROP_ZOOM, pspec);
+
+/**
+ * LdDiagramView::set-scroll-adjustments:
+ * @self: an #LdDiagramView object.
+ * @horizontal: the horizontal #GtkAdjustment.
+ * @vertical: the vertical #GtkAdjustment.
+ *
+ * Set scroll adjustments for the widget.
+ */
+	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 (LdDiagramViewClass, set_scroll_adjustments),
+		NULL, NULL,
+		ld_marshal_VOID__OBJECT_OBJECT,
+		G_TYPE_NONE, 2, GTK_TYPE_ADJUSTMENT, GTK_TYPE_ADJUSTMENT);
+
+/**
+ * LdDiagramView::cancel-operation:
+ * @self: an #LdDiagramView object.
+ *
+ * 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 (LdDiagramViewClass, cancel_operation), NULL, NULL,
+		g_cclosure_marshal_VOID__VOID,
+		G_TYPE_NONE, 0);
+
+/**
+ * LdDiagramView::move:
+ * @self: an #LdDiagramView object.
+ * @dx: The difference by which to move on the horizontal axis.
+ * @dy: The difference by which to move on the vertical axis.
+ *
+ * Move the selection, if any, or the document.
+ */
+	klass->move_signal = g_signal_new
+		("move", G_TYPE_FROM_CLASS (klass),
+		G_SIGNAL_RUN_LAST | G_SIGNAL_ACTION,
+		G_STRUCT_OFFSET (LdDiagramViewClass, move), NULL, NULL,
+		ld_marshal_VOID__DOUBLE_DOUBLE,
+		G_TYPE_NONE, 2, G_TYPE_DOUBLE, G_TYPE_DOUBLE);
+
+	g_type_class_add_private (klass, sizeof (LdDiagramViewPrivate));
+}
+
+static void
+ld_diagram_view_init (LdDiagramView *self)
+{
+	self->priv = G_TYPE_INSTANCE_GET_PRIVATE
+		(self, LD_TYPE_DIAGRAM_VIEW, LdDiagramViewPrivate);
+
+	self->priv->x = 0;
+	self->priv->y = 0;
+	self->priv->zoom = ZOOM_DEFAULT;
+
+	color_set (COLOR_GET (self, COLOR_BASE), 1, 1, 1, 1);
+	color_set (COLOR_GET (self, COLOR_GRID), 0.5, 0.5, 0.5, 1);
+	color_set (COLOR_GET (self, COLOR_OBJECT), 0, 0, 0, 1);
+	color_set (COLOR_GET (self, COLOR_SELECTION), 1, 0, 0, 1);
+	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_diagram_view_finalize (GObject *gobject)
+{
+	LdDiagramView *self;
+
+	self = LD_DIAGRAM_VIEW (gobject);
+
+	ld_diagram_view_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_diagram_view_parent_class)->finalize (gobject);
+}
+
+static void
+ld_diagram_view_get_property (GObject *object, guint property_id,
+	GValue *value, GParamSpec *pspec)
+{
+	LdDiagramView *self;
+
+	self = LD_DIAGRAM_VIEW (object);
+	switch (property_id)
+	{
+	case PROP_DIAGRAM:
+		g_value_set_object (value, ld_diagram_view_get_diagram (self));
+		break;
+	case PROP_LIBRARY:
+		g_value_set_object (value, ld_diagram_view_get_library (self));
+		break;
+	case PROP_ZOOM:
+		g_value_set_double (value, ld_diagram_view_get_zoom (self));
+		break;
+	default:
+		G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
+	}
+}
+
+static void
+ld_diagram_view_set_property (GObject *object, guint property_id,
+	const GValue *value, GParamSpec *pspec)
+{
+	LdDiagramView *self;
+
+	self = LD_DIAGRAM_VIEW (object);
+	switch (property_id)
+	{
+	case PROP_DIAGRAM:
+		ld_diagram_view_set_diagram (self,
+			LD_DIAGRAM (g_value_get_object (value)));
+		break;
+	case PROP_LIBRARY:
+		ld_diagram_view_set_library (self,
+			LD_LIBRARY (g_value_get_object (value)));
+		break;
+	case PROP_ZOOM:
+		ld_diagram_view_set_zoom (self, g_value_get_double (value));
+		break;
+	default:
+		G_OBJECT_WARN_INVALID_PROPERTY_ID (object, property_id, pspec);
+	}
+}
+
+static void
+ld_diagram_view_real_set_scroll_adjustments (LdDiagramView *self,
+	GtkAdjustment *horizontal, GtkAdjustment *vertical)
+{
+	/* TODO: Infinite area. */
+	GtkWidget *widget;
+	gdouble scale;
+
+	widget = GTK_WIDGET (self);
+	scale = ld_diagram_view_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, LdDiagramView *self)
+{
+	GtkWidget *widget;
+	gdouble scale;
+
+	widget = GTK_WIDGET (self);
+	scale = ld_diagram_view_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)
+{
+	LdDiagramView *self;
+
+	self = LD_DIAGRAM_VIEW (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 (LdDiagramView *self)
+{
+	gdouble scale;
+
+	scale = ld_diagram_view_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);
+	}
+}
+
+static void
+ld_diagram_view_real_move (LdDiagramView *self, gdouble dx, gdouble dy)
+{
+	LdDiagram *diagram;
+
+	diagram = self->priv->diagram;
+	if (!diagram)
+		return;
+
+	/* TODO: Check/move boundaries, also implement normal
+	 *       getters and setters for priv->x and priv->y.
+	 */
+	if (ld_diagram_get_selection (diagram))
+		move_selection (self, dx, dy);
+	else
+	{
+		self->priv->x += dx;
+		self->priv->y += dy;
+
+		simulate_motion (self);
+		update_adjustments (self);
+	}
+	gtk_widget_queue_draw (GTK_WIDGET (self));
+}
+
+
+/* ===== Generic interface etc. ============================================ */
+
+/**
+ * ld_diagram_view_new:
+ *
+ * Create an instance.
+ */
+GtkWidget *
+ld_diagram_view_new (void)
+{
+	return g_object_new (LD_TYPE_DIAGRAM_VIEW, NULL);
+}
+
+/**
+ * ld_diagram_view_set_diagram:
+ * @self: an #LdDiagramView object.
+ * @diagram: the #LdDiagram to be assigned to the view.
+ *
+ * Assign an #LdDiagram object to the view.
+ */
+void
+ld_diagram_view_set_diagram (LdDiagramView *self, LdDiagram *diagram)
+{
+	g_return_if_fail (LD_IS_DIAGRAM_VIEW (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_diagram_view_get_diagram:
+ * @self: an #LdDiagramView object.
+ *
+ * Get the #LdDiagram object assigned to this view.
+ * The reference count on the diagram is not incremented.
+ */
+LdDiagram *
+ld_diagram_view_get_diagram (LdDiagramView *self)
+{
+	g_return_val_if_fail (LD_IS_DIAGRAM_VIEW (self), NULL);
+	return self->priv->diagram;
+}
+
+static void
+diagram_connect_signals (LdDiagramView *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 (LdDiagramView *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_diagram_view_set_library:
+ * @self: an #LdDiagramView object.
+ * @library: the #LdLibrary to be assigned to the view.
+ *
+ * Assign an #LdLibrary object to the view.
+ */
+void
+ld_diagram_view_set_library (LdDiagramView *self, LdLibrary *library)
+{
+	g_return_if_fail (LD_IS_DIAGRAM_VIEW (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_diagram_view_get_library:
+ * @self: an #LdDiagramView object.
+ *
+ * Get the #LdLibrary object assigned to this view.
+ * The reference count on the library is not incremented.
+ */
+LdLibrary *
+ld_diagram_view_get_library (LdDiagramView *self)
+{
+	g_return_val_if_fail (LD_IS_DIAGRAM_VIEW (self), NULL);
+	return self->priv->library;
+}
+
+/*
+ * ld_diagram_view_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_diagram_view_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_DIAGRAM_VIEW_BASE_UNIT_LENGTH;
+}
+
+/*
+ * ld_diagram_view_get_scale_in_px:
+ * @self: an #LdDiagramView object.
+ *
+ * Return value: displayed length of the base unit in pixels.
+ */
+static gdouble
+ld_diagram_view_get_scale_in_px (LdDiagramView *self)
+{
+	g_return_val_if_fail (LD_IS_DIAGRAM_VIEW (self), 1);
+
+	return ld_diagram_view_get_base_unit_in_px (GTK_WIDGET (self))
+		* self->priv->zoom;
+}
+
+/**
+ * ld_diagram_view_widget_to_diagram_coords:
+ * @self: an #LdDiagramView 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 widget coordinates into diagram coordinates.
+ */
+void
+ld_diagram_view_widget_to_diagram_coords (LdDiagramView *self,
+	gdouble wx, gdouble wy, gdouble *dx, gdouble *dy)
+{
+	GtkWidget *widget;
+	gdouble scale;
+
+	g_return_if_fail (LD_IS_DIAGRAM_VIEW (self));
+	g_return_if_fail (dx != NULL);
+	g_return_if_fail (dy != NULL);
+
+	widget = GTK_WIDGET (self);
+	scale = ld_diagram_view_get_scale_in_px (self);
+
+	/* We know diagram coordinates of the center of view, 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_diagram_view_diagram_to_widget_coords:
+ * @self: an #LdDiagramView 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 widget coordinates.
+ */
+void
+ld_diagram_view_diagram_to_widget_coords (LdDiagramView *self,
+	gdouble dx, gdouble dy, gdouble *wx, gdouble *wy)
+{
+	GtkWidget *widget;
+	gdouble scale;
+
+	g_return_if_fail (LD_IS_DIAGRAM_VIEW (self));
+	g_return_if_fail (wx != NULL);
+	g_return_if_fail (wy != NULL);
+
+	widget = GTK_WIDGET (self);
+	scale = ld_diagram_view_get_scale_in_px (self);
+
+	/* Just the reversal of ld_diagram_view_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_diagram_view_get_zoom:
+ * @self: an #LdDiagramView object.
+ *
+ * Return value: zoom of the view.
+ */
+gdouble
+ld_diagram_view_get_zoom (LdDiagramView *self)
+{
+	g_return_val_if_fail (LD_IS_DIAGRAM_VIEW (self), -1);
+	return self->priv->zoom;
+}
+
+/**
+ * ld_diagram_view_set_zoom:
+ * @self: an #LdDiagramView object.
+ * @zoom: the zoom.
+ *
+ * Set zoom of the view.
+ */
+void
+ld_diagram_view_set_zoom (LdDiagramView *self, gdouble zoom)
+{
+	gdouble clamped_zoom;
+
+	g_return_if_fail (LD_IS_DIAGRAM_VIEW (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");
+}
+
+/**
+ * ld_diagram_view_can_zoom_in:
+ * @self: an #LdDiagramView object.
+ *
+ * Return value: %TRUE if the view can be zoomed in.
+ */
+gboolean
+ld_diagram_view_can_zoom_in (LdDiagramView *self)
+{
+	g_return_val_if_fail (LD_IS_DIAGRAM_VIEW (self), FALSE);
+	return self->priv->zoom < ZOOM_MAX;
+}
+
+/**
+ * ld_diagram_view_can_zoom_out:
+ * @self: an #LdDiagramView object.
+ *
+ * Return value: %TRUE if the view can be zoomed out.
+ */
+gboolean
+ld_diagram_view_can_zoom_out (LdDiagramView *self)
+{
+	g_return_val_if_fail (LD_IS_DIAGRAM_VIEW (self), FALSE);
+	return self->priv->zoom > ZOOM_MIN;
+}
+
+/**
+ * ld_diagram_view_zoom_in:
+ * @self: an #LdDiagramView object.
+ *
+ * Zoom the view in.
+ */
+void
+ld_diagram_view_zoom_in (LdDiagramView *self)
+{
+	g_return_if_fail (LD_IS_DIAGRAM_VIEW (self));
+	ld_diagram_view_set_zoom (self, self->priv->zoom * ZOOM_STEP);
+}
+
+/**
+ * ld_diagram_view_zoom_out:
+ * @self: an #LdDiagramView object.
+ *
+ * Zoom the view out.
+ */
+void
+ld_diagram_view_zoom_out (LdDiagramView *self)
+{
+	g_return_if_fail (LD_IS_DIAGRAM_VIEW (self));
+	ld_diagram_view_set_zoom (self, self->priv->zoom / ZOOM_STEP);
+}
+
+
+/* ===== Helper functions ================================================== */
+
+static void
+color_set (Color *color, gdouble r, gdouble g, gdouble b, gdouble a)
+{
+	color->r = r;
+	color->g = g;
+	color->b = b;
+	color->a = a;
+}
+
+static void
+color_apply (Color *color, cairo_t *cr)
+{
+	cairo_set_source_rgba (cr, color->r, color->g, color->b, color->a);
+}
+
+static guint32
+color_to_cairo_argb (Color *color)
+{
+	return (guint) (color->a            * 255) << 24
+	     | (guint) (color->r * color->a * 255) << 16
+	     | (guint) (color->g * color->a * 255) << 8
+	     | (guint) (color->b * color->a * 255);
+}
+
+static gdouble
+point_to_line_segment_distance
+	(const LdPoint *point, const LdPoint *p1, const LdPoint *p2)
+{
+	gdouble dx, dy, u;
+
+	dx = p2->x - p1->x;
+	dy = p2->y - p1->y;
+
+	if (dx == 0. && dy == 0.)
+		return ld_point_distance (point, p1->x, p1->y);
+
+	/* Find projection of the point onto the line. */
+	u = ((point->x - p1->x) * dx + (point->y - p1->y) * dy)
+		/ (dx * dx + dy * dy);
+
+	/* The projection is beyond the line segment. */
+	if (u < 0.)
+		return ld_point_distance (point, p1->x, p1->y);
+	else if (u > 1.)
+		return ld_point_distance (point, p2->x, p2->y);
+
+	/* The projection is on the line segment. */
+	return ld_point_distance (point, p1->x + u * dx, p1->y + u * dy);
+}
+
+
+/* ===== Generic functions ================================================= */
+
+static gboolean
+object_hit_test (LdDiagramView *self, LdDiagramObject *object,
+	const LdPoint *point)
+{
+	if (LD_IS_DIAGRAM_SYMBOL (object))
+		return symbol_hit_test (self,
+			LD_DIAGRAM_SYMBOL (object), point);
+	if (LD_IS_DIAGRAM_CONNECTION (object))
+		return connection_hit_test (self,
+			LD_DIAGRAM_CONNECTION (object), point);
+	return FALSE;
+}
+
+static gboolean
+get_object_clip_area (LdDiagramView *self,
+	LdDiagramObject *object, LdRectangle *rect)
+{
+	if (LD_IS_DIAGRAM_SYMBOL (object))
+		return get_symbol_clip_area (self,
+			LD_DIAGRAM_SYMBOL (object), rect);
+	if (LD_IS_DIAGRAM_CONNECTION (object))
+		return get_connection_clip_area (self,
+			LD_DIAGRAM_CONNECTION (object), rect);
+	return FALSE;
+}
+
+static void
+move_object_to_point (LdDiagramView *self, LdDiagramObject *object,
+	const LdPoint *point)
+{
+	gdouble diagram_x, diagram_y;
+
+	ld_diagram_view_widget_to_diagram_coords (self,
+		point->x, point->y, &diagram_x, &diagram_y);
+	g_object_set (object,
+		"x", floor (diagram_x + 0.5),
+		"y", floor (diagram_y + 0.5),
+		NULL);
+}
+
+static LdDiagramObject *
+get_object_at_point (LdDiagramView *self, const LdPoint *point)
+{
+	GList *objects, *iter;
+
+	/* Iterate from the top object downwards. */
+	objects = (GList *) ld_diagram_get_objects (self->priv->diagram);
+	for (iter = g_list_last (objects); iter; iter = g_list_previous (iter))
+	{
+		LdDiagramObject *object;
+
+		object = LD_DIAGRAM_OBJECT (iter->data);
+		if (object_hit_test (self, object, point))
+			return object;
+	}
+	return NULL;
+}
+
+static void
+move_selection (LdDiagramView *self, gdouble dx, gdouble dy)
+{
+	LdDiagram *diagram;
+	GList *selection, *iter;
+
+	diagram = self->priv->diagram;
+	if (!diagram)
+		return;
+
+	selection = ld_diagram_get_selection (diagram);
+	if (!selection)
+		return;
+
+	ld_diagram_begin_user_action (diagram);
+	for (iter = selection; iter; iter = g_list_next (iter))
+	{
+		gdouble x, y;
+
+		g_object_get (iter->data, "x", &x, "y", &y, NULL);
+		x += dx;
+		y += dy;
+		g_object_set (iter->data, "x", x, "y", y, NULL);
+	}
+	ld_diagram_end_user_action (diagram);
+}
+
+static gboolean
+is_object_selected (LdDiagramView *self, LdDiagramObject *object)
+{
+	return g_list_find (ld_diagram_get_selection (self->priv->diagram),
+		object) != NULL;
+}
+
+static void
+queue_draw (LdDiagramView *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 (LdDiagramView *self, LdDiagramObject *object)
+{
+	LdRectangle rect;
+
+	if (!get_object_clip_area (self, object, &rect))
+		return;
+	queue_draw (self, &rect);
+}
+
+
+/* ===== Symbol terminals ================================================== */
+
+static void
+check_terminals (LdDiagramView *self, const LdPoint *point)
+{
+	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))
+	{
+		gdouble object_x, object_y;
+		LdDiagramSymbol *diagram_symbol;
+		LdSymbol *symbol;
+		const LdPointArray *terminals;
+		guint i;
+		gint rotation;
+
+		if (!LD_IS_DIAGRAM_SYMBOL (iter->data))
+			continue;
+
+		diagram_symbol = LD_DIAGRAM_SYMBOL (iter->data);
+		symbol = resolve_symbol (self, diagram_symbol);
+		if (!symbol)
+			continue;
+
+		g_object_get (diagram_symbol, "x", &object_x, "y", &object_y,
+			"rotation", &rotation, NULL);
+
+		terminals = ld_symbol_get_terminals (symbol);
+		for (i = 0; i < terminals->length; i++)
+		{
+			LdPoint cur_term, widget_coords;
+			gdouble distance;
+
+			cur_term = terminals->points[i];
+			rotate_terminal (&cur_term, rotation);
+			cur_term.x += object_x;
+			cur_term.y += object_y;
+
+			ld_diagram_view_diagram_to_widget_coords (self,
+				cur_term.x, cur_term.y, &widget_coords.x, &widget_coords.y);
+			distance = ld_point_distance (&widget_coords, point->x, point->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_hovered = TRUE;
+		self->priv->terminal = closest_terminal;
+		queue_terminal_draw (self, &closest_terminal);
+	}
+}
+
+static void
+rotate_terminal (LdPoint *terminal, gint symbol_rotation)
+{
+	gdouble temp;
+
+	switch (symbol_rotation)
+	{
+	case LD_DIAGRAM_SYMBOL_ROTATION_90:
+		temp = terminal->y;
+		terminal->y = terminal->x;
+		terminal->x = -temp;
+		break;
+	case LD_DIAGRAM_SYMBOL_ROTATION_180:
+		terminal->y = -terminal->y;
+		terminal->x = -terminal->x;
+		break;
+	case LD_DIAGRAM_SYMBOL_ROTATION_270:
+		temp = terminal->x;
+		terminal->x = terminal->y;
+		terminal->y = -temp;
+		break;
+	}
+}
+
+static void
+hide_terminals (LdDiagramView *self)
+{
+	if (self->priv->terminal_hovered)
+	{
+		self->priv->terminal_hovered = FALSE;
+		queue_terminal_draw (self, &self->priv->terminal);
+	}
+}
+
+static void
+queue_terminal_draw (LdDiagramView *self, LdPoint *terminal)
+{
+	LdRectangle rect;
+	LdPoint widget_coords;
+
+	ld_diagram_view_diagram_to_widget_coords (self,
+		terminal->x, terminal->y, &widget_coords.x, &widget_coords.y);
+
+	rect.x = widget_coords.x - TERMINAL_RADIUS;
+	rect.y = widget_coords.y - TERMINAL_RADIUS;
+	rect.width  = 2 * TERMINAL_RADIUS;
+	rect.height = 2 * TERMINAL_RADIUS;
+
+	queue_draw (self, &rect);
+}
+
+
+/* ===== Diagram symbol ==================================================== */
+
+static gboolean
+symbol_hit_test (LdDiagramView *self, LdDiagramSymbol *symbol,
+	const LdPoint *point)
+{
+	LdRectangle rect;
+
+	if (!get_symbol_area (self, symbol, &rect))
+		return FALSE;
+	ld_rectangle_extend (&rect, OBJECT_BORDER_TOLERANCE);
+	return ld_rectangle_contains_point (&rect, point);
+}
+
+static gboolean
+get_symbol_clip_area (LdDiagramView *self,
+	LdDiagramSymbol *symbol, LdRectangle *rect)
+{
+	LdRectangle object_rect;
+
+	if (!get_symbol_area (self, symbol, &object_rect))
+		return FALSE;
+
+	*rect = object_rect;
+	ld_rectangle_extend (rect, SYMBOL_CLIP_TOLERANCE);
+	return TRUE;
+}
+
+static gboolean
+get_symbol_area (LdDiagramView *self, LdDiagramSymbol *symbol,
+	LdRectangle *rect)
+{
+	gdouble object_x, object_y;
+	LdSymbol *library_symbol;
+	LdRectangle area;
+	gdouble x1, x2;
+	gdouble y1, y2;
+	gint rotation;
+
+	g_object_get (symbol, "x", &object_x, "y", &object_y,
+		"rotation", &rotation, NULL);
+
+	library_symbol = resolve_symbol (self, symbol);
+	if (library_symbol)
+		ld_symbol_get_area (library_symbol, &area);
+	else
+		return FALSE;
+
+	rotate_symbol_area (&area, rotation);
+
+	ld_diagram_view_diagram_to_widget_coords (self,
+		object_x + area.x,
+		object_y + area.y,
+		&x1, &y1);
+	ld_diagram_view_diagram_to_widget_coords (self,
+		object_x + area.x + area.width,
+		object_y + area.y + area.height,
+		&x2, &y2);
+
+	x1 = floor (x1);
+	y1 = floor (y1);
+	x2 = ceil (x2);
+	y2 = ceil (y2);
+
+	rect->x = x1;
+	rect->y = y1;
+	rect->width  = x2 - x1;
+	rect->height = y2 - y1;
+	return TRUE;
+}
+
+static void
+rotate_symbol_area (LdRectangle *area, gint rotation)
+{
+	gdouble temp;
+
+	switch (rotation)
+	{
+	case LD_DIAGRAM_SYMBOL_ROTATION_90:
+		temp = area->y;
+		area->y = area->x;
+		area->x = -(temp + area->height);
+		break;
+	case LD_DIAGRAM_SYMBOL_ROTATION_180:
+		area->y = -(area->y + area->height);
+		area->x = -(area->x + area->width);
+		break;
+	case LD_DIAGRAM_SYMBOL_ROTATION_270:
+		temp = area->x;
+		area->x = area->y;
+		area->y = -(temp + area->width);
+		break;
+	}
+
+	switch (rotation)
+	{
+	case LD_DIAGRAM_SYMBOL_ROTATION_90:
+	case LD_DIAGRAM_SYMBOL_ROTATION_270:
+		temp = area->width;
+		area->width = area->height;
+		area->height = temp;
+		break;
+	}
+}
+
+static void
+rotate_symbol (LdDiagramView *self, LdDiagramSymbol *symbol)
+{
+	gint rotation;
+
+	g_object_get (symbol, "rotation", &rotation, NULL);
+	queue_object_draw (self, LD_DIAGRAM_OBJECT (symbol));
+
+	switch (rotation)
+	{
+	case LD_DIAGRAM_SYMBOL_ROTATION_0:
+		rotation = LD_DIAGRAM_SYMBOL_ROTATION_90;
+		break;
+	case LD_DIAGRAM_SYMBOL_ROTATION_90:
+		rotation = LD_DIAGRAM_SYMBOL_ROTATION_180;
+		break;
+	case LD_DIAGRAM_SYMBOL_ROTATION_180:
+		rotation = LD_DIAGRAM_SYMBOL_ROTATION_270;
+		break;
+	case LD_DIAGRAM_SYMBOL_ROTATION_270:
+		rotation = LD_DIAGRAM_SYMBOL_ROTATION_0;
+		break;
+	}
+
+	g_object_set (symbol, "rotation", rotation, NULL);
+	queue_object_draw (self, LD_DIAGRAM_OBJECT (symbol));
+}
+
+static LdSymbol *
+resolve_symbol (LdDiagramView *self, LdDiagramSymbol *diagram_symbol)
+{
+	LdSymbol *symbol;
+	gchar *klass;
+
+	if (!self->priv->library)
+		return NULL;
+
+	klass = ld_diagram_symbol_get_class (diagram_symbol);
+	symbol = ld_library_find_symbol (self->priv->library, klass);
+	g_free (klass);
+	return symbol;
+}
+
+
+/* ===== Diagram connection ================================================ */
+
+static gboolean
+connection_hit_test (LdDiagramView *self, LdDiagramConnection *connection,
+	const LdPoint *point)
+{
+	gdouble object_x, object_y, length;
+	LdPointArray *points;
+	guint i;
+
+	g_object_get (connection, "x", &object_x, "y", &object_y, NULL);
+
+	points = ld_diagram_connection_get_points (connection);
+	if (points->length < 2)
+	{
+		ld_point_array_free (points);
+		return FALSE;
+	}
+
+	for (i = 0; i < points->length; i++)
+	{
+		ld_diagram_view_diagram_to_widget_coords (self,
+			points->points[i].x + object_x,
+			points->points[i].y + object_y,
+			&points->points[i].x,
+			&points->points[i].y);
+
+		if (!i)
+			continue;
+
+		length = point_to_line_segment_distance
+			(point, &points->points[i - 1], &points->points[i]);
+		if (length <= OBJECT_BORDER_TOLERANCE)
+		{
+			ld_point_array_free (points);
+			return TRUE;
+		}
+	}
+	ld_point_array_free (points);
+	return FALSE;
+}
+
+static gboolean
+get_connection_clip_area (LdDiagramView *self,
+	LdDiagramConnection *connection, LdRectangle *rect)
+{
+	return get_connection_area (self, connection, rect);
+}
+
+static gboolean
+get_connection_area (LdDiagramView *self,
+	LdDiagramConnection *connection, LdRectangle *rect)
+{
+	gdouble x_origin, y_origin;
+	gdouble x, y, x_min, x_max, y_min, y_max;
+	LdPointArray *points;
+	guint i;
+
+	points = ld_diagram_connection_get_points (connection);
+	if (!points->length)
+	{
+		ld_point_array_free (points);
+		return FALSE;
+	}
+
+	g_object_get (connection, "x", &x_origin, "y", &y_origin, NULL);
+
+	ld_diagram_view_diagram_to_widget_coords (self,
+		x_origin + points->points[0].x,
+		y_origin + points->points[0].y,
+		&x, &y);
+
+	x_max = x_min = x;
+	y_max = y_min = y;
+
+	for (i = 1; i < points->length; i++)
+	{
+		ld_diagram_view_diagram_to_widget_coords (self,
+			x_origin + points->points[i].x,
+			y_origin + points->points[i].y,
+			&x, &y);
+
+		if (x < x_min)
+			x_min = x;
+		else if (x > x_max)
+			x_max = x;
+
+		if (y < y_min)
+			y_min = y;
+		else if (y > y_max)
+			y_max = y;
+	}
+
+	rect->x = x_min;
+	rect->y = y_min;
+	rect->width  = x_max - x_min;
+	rect->height = y_max - y_min;
+
+	ld_point_array_free (points);
+	return TRUE;
+}
+
+
+/* ===== Operations ======================================================== */
+
+static void
+ld_diagram_view_real_cancel_operation (LdDiagramView *self)
+{
+	g_return_if_fail (LD_IS_DIAGRAM_VIEW (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_diagram_view_add_object_begin:
+ * @self: an #LdDiagramView object.
+ * @object: (transfer full): the object to be added to the diagram.
+ *
+ * Begin an operation for adding an object into the diagram.
+ */
+void
+ld_diagram_view_add_object_begin (LdDiagramView *self, LdDiagramObject *object)
+{
+	AddObjectData *data;
+
+	g_return_if_fail (LD_IS_DIAGRAM_VIEW (self));
+	g_return_if_fail (LD_IS_DIAGRAM_OBJECT (object));
+
+	g_signal_emit (self,
+		LD_DIAGRAM_VIEW_GET_CLASS (self)->cancel_operation_signal, 0);
+
+	self->priv->operation = OPER_ADD_OBJECT;
+	self->priv->operation_end = oper_add_object_end;
+
+	data = &OPER_DATA (self, add_object);
+	data->object = object;
+}
+
+static void
+oper_add_object_end (LdDiagramView *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;
+	}
+}
+
+static void
+oper_connect_begin (LdDiagramView *self, const LdPoint *point)
+{
+	ConnectData *data;
+
+	g_signal_emit (self,
+		LD_DIAGRAM_VIEW_GET_CLASS (self)->cancel_operation_signal, 0);
+
+	self->priv->operation = OPER_CONNECT;
+	self->priv->operation_end = oper_connect_end;
+
+	data = &OPER_DATA (self, connect);
+	data->connection = ld_diagram_connection_new (NULL);
+
+	data->origin = self->priv->terminal;
+	g_object_set (data->connection,
+		"x", data->origin.x,
+		"y", data->origin.y,
+		NULL);
+
+	self->priv->terminal_hovered = FALSE;
+
+	oper_connect_motion (self, point);
+}
+
+static void
+oper_connect_end (LdDiagramView *self)
+{
+	ConnectData *data;
+
+	data = &OPER_DATA (self, connect);
+	queue_object_draw (self, LD_DIAGRAM_OBJECT (data->connection));
+
+	ld_diagram_insert_object (self->priv->diagram,
+		LD_DIAGRAM_OBJECT (data->connection), -1);
+
+	g_object_unref (data->connection);
+}
+
+static void
+oper_connect_motion (LdDiagramView *self, const LdPoint *point)
+{
+	ConnectData *data;
+	LdPointArray *points;
+	gdouble diagram_x, diagram_y;
+
+	data = &OPER_DATA (self, connect);
+
+	/* Find an orthogonal path between the points. */
+	/* TODO: This alghorithm is pretty lame, needs to be improved. */
+	points = ld_point_array_sized_new (4);
+	points->length = 4;
+
+	points->points[0].x = 0;
+	points->points[0].y = 0;
+
+	ld_diagram_view_widget_to_diagram_coords (self,
+		point->x, point->y, &diagram_x, &diagram_y);
+	points->points[3].x = floor (diagram_x - data->origin.x + 0.5);
+	points->points[3].y = floor (diagram_y - data->origin.y + 0.5);
+
+	if (ABS (points->points[3].x) > ABS (points->points[3].y))
+	{
+		points->points[1].x = points->points[3].x / 2;
+		points->points[1].y = 0;
+		points->points[2].x = points->points[3].x / 2;
+		points->points[2].y = points->points[3].y;
+	}
+	else
+	{
+		points->points[1].x = 0;
+		points->points[1].y = points->points[3].y / 2;
+		points->points[2].x = points->points[3].x;
+		points->points[2].y = points->points[3].y / 2;
+	}
+
+	queue_object_draw (self, LD_DIAGRAM_OBJECT (data->connection));
+	ld_diagram_connection_set_points (data->connection, points);
+	queue_object_draw (self, LD_DIAGRAM_OBJECT (data->connection));
+	ld_point_array_free (points);
+
+	check_terminals (self, point);
+
+	if (self->priv->terminal.x == data->origin.x
+		&& self->priv->terminal.y == data->origin.y)
+		self->priv->terminal_hovered = FALSE;
+}
+
+static void
+oper_select_begin (LdDiagramView *self, const LdPoint *point)
+{
+	SelectData *data;
+
+	g_signal_emit (self,
+		LD_DIAGRAM_VIEW_GET_CLASS (self)->cancel_operation_signal, 0);
+
+	self->priv->operation = OPER_SELECT;
+	self->priv->operation_end = oper_select_end;
+
+	data = &OPER_DATA (self, select);
+	data->drag_last_pos.x = self->priv->drag_start_pos.x;
+	data->drag_last_pos.y = self->priv->drag_start_pos.y;
+
+	oper_select_motion (self, point);
+}
+
+static void
+oper_select_end (LdDiagramView *self)
+{
+	oper_select_queue_draw (self);
+}
+
+static void
+oper_select_get_rectangle (LdDiagramView *self, LdRectangle *rect)
+{
+	SelectData *data;
+
+	data = &OPER_DATA (self, select);
+	rect->x = MIN (self->priv->drag_start_pos.x, data->drag_last_pos.x);
+	rect->y = MIN (self->priv->drag_start_pos.y, data->drag_last_pos.y);
+	rect->width  = ABS (self->priv->drag_start_pos.x - data->drag_last_pos.x);
+	rect->height = ABS (self->priv->drag_start_pos.y - data->drag_last_pos.y);
+}
+
+static void
+oper_select_queue_draw (LdDiagramView *self)
+{
+	LdRectangle rect;
+	SelectData *data;
+
+	data = &OPER_DATA (self, select);
+	oper_select_get_rectangle (self, &rect);
+	queue_draw (self, &rect);
+}
+
+static void
+oper_select_draw (GtkWidget *widget, DrawData *data)
+{
+	static const double dashes[] = {3, 5};
+	SelectData *select_data;
+
+	g_return_if_fail (data->self->priv->operation == OPER_SELECT);
+
+	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_SQUARE);
+	cairo_set_dash (data->cr, dashes, G_N_ELEMENTS (dashes), 0);
+
+	select_data = &OPER_DATA (data->self, select);
+
+	cairo_rectangle (data->cr,
+		data->self->priv->drag_start_pos.x - 0.5,
+		data->self->priv->drag_start_pos.y - 0.5,
+		select_data->drag_last_pos.x - data->self->priv->drag_start_pos.x + 1,
+		select_data->drag_last_pos.y - data->self->priv->drag_start_pos.y + 1);
+	cairo_stroke (data->cr);
+}
+
+static void
+oper_select_motion (LdDiagramView *self, const LdPoint *point)
+{
+	SelectData *data;
+	GList *objects, *iter;
+	LdRectangle selection_rect, rect;
+
+	data = &OPER_DATA (self, select);
+
+	oper_select_queue_draw (self);
+	data->drag_last_pos = *point;
+	oper_select_queue_draw (self);
+
+	oper_select_get_rectangle (self, &selection_rect);
+	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 (LD_IS_DIAGRAM_SYMBOL (object))
+		{
+			if (!get_symbol_area (self,
+				LD_DIAGRAM_SYMBOL (object), &rect))
+				continue;
+		}
+		else if (LD_IS_DIAGRAM_CONNECTION (object))
+		{
+			if (!get_connection_area (self,
+				LD_DIAGRAM_CONNECTION (object), &rect))
+				continue;
+		}
+
+		ld_rectangle_extend (&rect, OBJECT_BORDER_TOLERANCE);
+		if (ld_rectangle_contains (&selection_rect, &rect))
+			ld_diagram_select (self->priv->diagram, object);
+		else
+			ld_diagram_unselect (self->priv->diagram, object);
+	}
+}
+
+static void
+oper_move_selection_begin (LdDiagramView *self, const LdPoint *point)
+{
+	MoveSelectionData *data;
+
+	g_signal_emit (self,
+		LD_DIAGRAM_VIEW_GET_CLASS (self)->cancel_operation_signal, 0);
+
+	self->priv->operation = OPER_MOVE_SELECTION;
+	self->priv->operation_end = oper_move_selection_end;
+
+	ld_diagram_begin_user_action (self->priv->diagram);
+
+	data = &OPER_DATA (self, move_selection);
+	data->move_origin = self->priv->drag_start_pos;
+
+	oper_move_selection_motion (self, point);
+}
+
+static void
+oper_move_selection_end (LdDiagramView *self)
+{
+	ld_diagram_end_user_action (self->priv->diagram);
+}
+
+static void
+oper_move_selection_motion (LdDiagramView *self, const LdPoint *point)
+{
+	MoveSelectionData *data;
+	gdouble scale, dx, dy, move_x, move_y;
+	gdouble move = FALSE;
+
+	scale = ld_diagram_view_get_scale_in_px (self);
+	data = &OPER_DATA (self, move_selection);
+
+	dx = point->x - data->move_origin.x;
+	dy = point->y - data->move_origin.y;
+
+	move_x = dx < 0 ? ceil (dx / scale) : floor (dx / scale);
+	move_y = dy < 0 ? ceil (dy / scale) : floor (dy / scale);
+
+	if (ABS (move_x) >= 1)
+	{
+		data->move_origin.x += move_x * scale;
+		move = TRUE;
+	}
+	if (ABS (move_y) >= 1)
+	{
+		data->move_origin.y += move_y * scale;
+		move = TRUE;
+	}
+
+	if (move)
+		move_selection (self, move_x, move_y);
+}
+
+
+/* ===== Events, rendering ================================================= */
+
+static void
+simulate_motion (LdDiagramView *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)
+{
+	LdPoint point;
+	LdDiagramView *self;
+	AddObjectData *add_data;
+
+	point.x = event->x;
+	point.y = event->y;
+
+	self = LD_DIAGRAM_VIEW (widget);
+	switch (self->priv->operation)
+	{
+	case OPER_ADD_OBJECT:
+		add_data = &OPER_DATA (self, add_object);
+		add_data->visible = TRUE;
+
+		queue_object_draw (self, add_data->object);
+		move_object_to_point (self, add_data->object, &point);
+		queue_object_draw (self, add_data->object);
+		break;
+	case OPER_CONNECT:
+		oper_connect_motion (self, &point);
+		break;
+	case OPER_SELECT:
+		oper_select_motion (self, &point);
+		break;
+	case OPER_MOVE_SELECTION:
+		oper_move_selection_motion (self, &point);
+		break;
+	case OPER_0:
+		if (event->state & GDK_BUTTON1_MASK
+			&& (event->x != self->priv->drag_start_pos.x
+			|| event->y != self->priv->drag_start_pos.y))
+		{
+			switch (self->priv->drag_operation)
+			{
+			case OPER_CONNECT:
+				oper_connect_begin (self, &point);
+				break;
+			case OPER_SELECT:
+				oper_select_begin (self, &point);
+				break;
+			case OPER_MOVE_SELECTION:
+				oper_move_selection_begin (self, &point);
+				break;
+			}
+		}
+		check_terminals (self, &point);
+		break;
+	}
+	return FALSE;
+}
+
+static gboolean
+on_leave_notify (GtkWidget *widget, GdkEventCrossing *event, gpointer user_data)
+{
+	LdDiagramView *self;
+
+	self = LD_DIAGRAM_VIEW (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)
+{
+	LdPoint point;
+	LdDiagramView *self;
+	AddObjectData *data;
+	LdDiagramObject *object;
+
+	point.x = event->x;
+	point.y = event->y;
+
+	self = LD_DIAGRAM_VIEW (widget);
+	if (!self->priv->diagram)
+		return FALSE;
+
+	if (event->button == 3 && self->priv->operation == OPER_0)
+	{
+		object = get_object_at_point (self, &point);
+		if (object && LD_IS_DIAGRAM_SYMBOL (object))
+			rotate_symbol (self, LD_DIAGRAM_SYMBOL (object));
+		return FALSE;
+	}
+
+	if (event->button != 1)
+		return FALSE;
+	if (!gtk_widget_has_focus (widget))
+		gtk_widget_grab_focus (widget);
+
+	self->priv->drag_operation = OPER_0;
+	switch (self->priv->operation)
+	{
+	case OPER_ADD_OBJECT:
+		data = &OPER_DATA (self, add_object);
+
+		queue_object_draw (self, data->object);
+		move_object_to_point (self, data->object, &point);
+		ld_diagram_insert_object (self->priv->diagram, data->object, -1);
+
+		/* XXX: "cancel" causes confusion. */
+		g_signal_emit (self,
+			LD_DIAGRAM_VIEW_GET_CLASS (self)->cancel_operation_signal, 0);
+		break;
+	case OPER_0:
+		self->priv->drag_start_pos = point;
+
+		if (self->priv->terminal_hovered)
+		{
+			self->priv->drag_operation = OPER_CONNECT;
+			break;
+		}
+
+		object = get_object_at_point (self, &point);
+		if (!object)
+		{
+			ld_diagram_unselect_all (self->priv->diagram);
+			self->priv->drag_operation = OPER_SELECT;
+		}
+		else if (!is_object_selected (self, object))
+		{
+			if (event->state != GDK_SHIFT_MASK)
+				ld_diagram_unselect_all (self->priv->diagram);
+			ld_diagram_select (self->priv->diagram, object);
+			self->priv->drag_operation = OPER_MOVE_SELECTION;
+		}
+		else
+			self->priv->drag_operation = OPER_MOVE_SELECTION;
+		break;
+	}
+	return FALSE;
+}
+
+static gboolean
+on_button_release (GtkWidget *widget, GdkEventButton *event, gpointer user_data)
+{
+	LdPoint point;
+	LdDiagramView *self;
+	LdDiagramObject *object;
+
+	if (event->button != 1)
+		return FALSE;
+
+	point.x = event->x;
+	point.y = event->y;
+
+	self = LD_DIAGRAM_VIEW (widget);
+	if (!self->priv->diagram)
+		return FALSE;
+
+	switch (self->priv->operation)
+	{
+	case OPER_SELECT:
+	case OPER_MOVE_SELECTION:
+	case OPER_CONNECT:
+		g_signal_emit (self,
+			LD_DIAGRAM_VIEW_GET_CLASS (self)->cancel_operation_signal, 0);
+		break;
+	case OPER_0:
+		object = get_object_at_point (self, &point);
+		if (object && is_object_selected (self, object))
+		{
+			if (!(event->state & GDK_SHIFT_MASK))
+				ld_diagram_unselect_all (self->priv->diagram);
+			ld_diagram_select (self->priv->diagram, object);
+		}
+		break;
+	}
+	return FALSE;
+}
+
+static gboolean
+on_scroll (GtkWidget *widget, GdkEventScroll *event, gpointer user_data)
+{
+	gdouble prev_x, prev_y;
+	gdouble new_x, new_y;
+	LdPoint point;
+	LdDiagramView *self;
+
+	point.x = event->x;
+	point.y = event->y;
+	self = LD_DIAGRAM_VIEW (widget);
+
+	ld_diagram_view_widget_to_diagram_coords (self,
+		event->x, event->y, &prev_x, &prev_y);
+
+	switch (event->direction)
+	{
+	case GDK_SCROLL_UP:
+		ld_diagram_view_zoom_in (self);
+		break;
+	case GDK_SCROLL_DOWN:
+		ld_diagram_view_zoom_out (self);
+		break;
+	default:
+		return FALSE;
+	}
+
+	ld_diagram_view_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, &point);
+	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_DIAGRAM_VIEW (widget);
+	data.scale = ld_diagram_view_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);
+
+	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);
+
+	if (data.self->priv->operation == OPER_SELECT)
+		oper_select_draw (widget, &data);
+
+	cairo_destroy (data.cr);
+	return FALSE;
+}
+
+static void
+draw_grid (GtkWidget *widget, DrawData *data)
+{
+	gdouble grid_step;
+	gint grid_factor;
+	gdouble x_init, y_init;
+	gdouble x, y;
+	cairo_surface_t *grid_surface;
+	gint stride;
+	unsigned char *pixels;
+	guint32 color;
+
+	grid_step = data->scale;
+	grid_factor = 1;
+	while (grid_step < 5)
+	{
+		grid_step *= 5;
+		grid_factor *= 5;
+	}
+
+	/* Paint manually on our own raster surface for speed. */
+	stride = cairo_format_stride_for_width
+		(CAIRO_FORMAT_ARGB32, data->exposed_rect.width);
+	pixels = g_malloc0 (stride * data->exposed_rect.height);
+	grid_surface = cairo_image_surface_create_for_data
+		(pixels, CAIRO_FORMAT_ARGB32,
+		data->exposed_rect.width, data->exposed_rect.height, stride);
+
+	/* Get coordinates of the top-left point. */
+	ld_diagram_view_widget_to_diagram_coords (data->self,
+		data->exposed_rect.x, data->exposed_rect.y, &x_init, &y_init);
+
+	x_init = ceil (x_init);
+	x_init = x_init - (gint) x_init % grid_factor;
+	y_init = ceil (y_init);
+	y_init = y_init - (gint) y_init % grid_factor;
+
+	ld_diagram_view_diagram_to_widget_coords (data->self,
+		x_init, y_init, &x_init, &y_init);
+
+	x_init -= data->exposed_rect.x;
+	y_init -= data->exposed_rect.y;
+
+	while (x_init < 0)
+		x_init += grid_step;
+	while (y_init < 0)
+		y_init += grid_step;
+
+	color = color_to_cairo_argb (COLOR_GET (data->self, COLOR_GRID));
+
+	for     (x = x_init; x < data->exposed_rect.width;  x += grid_step)
+		for (y = y_init; y < data->exposed_rect.height; y += grid_step)
+			*((guint32 *) (pixels + stride * (gint) y) + (gint) x) = color;
+
+	cairo_set_source_surface (data->cr, grid_surface,
+		data->exposed_rect.x, data->exposed_rect.y);
+	cairo_paint (data->cr);
+
+	cairo_surface_destroy (grid_surface);
+	g_free (pixels);
+}
+
+static void
+draw_terminal (GtkWidget *widget, DrawData *data)
+{
+	LdDiagramViewPrivate *priv;
+	LdPoint widget_coords;
+
+	priv = data->self->priv;
+	if (!priv->terminal_hovered)
+		return;
+
+	color_apply (COLOR_GET (data->self, COLOR_TERMINAL), data->cr);
+	cairo_set_line_width (data->cr, 1);
+
+	cairo_new_path (data->cr);
+	ld_diagram_view_diagram_to_widget_coords (data->self,
+		priv->terminal.x, priv->terminal.y,
+		&widget_coords.x, &widget_coords.y);
+	cairo_arc (data->cr, widget_coords.x, widget_coords.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 = objects; iter; iter = g_list_next (iter))
+		draw_object (LD_DIAGRAM_OBJECT (iter->data), data);
+
+	switch (data->self->priv->operation)
+	{
+		AddObjectData *add_data;
+		ConnectData *connect_data;
+
+	case OPER_ADD_OBJECT:
+		add_data = &OPER_DATA (data->self, add_object);
+		if (add_data->visible)
+			draw_object (add_data->object, data);
+		break;
+	case OPER_CONNECT:
+		connect_data = &OPER_DATA (data->self, connect);
+		draw_object (LD_DIAGRAM_OBJECT (connect_data->connection), 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))
+		color_apply (COLOR_GET (data->self, COLOR_SELECTION), data->cr);
+	else
+		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);
+	else if (LD_IS_DIAGRAM_CONNECTION (diagram_object))
+		draw_connection (LD_DIAGRAM_CONNECTION (diagram_object), data);
+}
+
+static void
+draw_symbol (LdDiagramSymbol *diagram_symbol, DrawData *data)
+{
+	LdSymbol *symbol;
+	LdRectangle clip_rect;
+	gdouble x, y;
+	gint rotation;
+
+	symbol = resolve_symbol (data->self, diagram_symbol);
+
+	/* TODO: Resolve this better; draw a cross or whatever. */
+	if (!symbol)
+	{
+		gchar *klass;
+
+		klass = ld_diagram_symbol_get_class (diagram_symbol);
+		g_warning ("cannot find symbol `%s' in the library", klass);
+		g_free (klass);
+		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);
+
+	g_object_get (diagram_symbol, "x", &x, "y", &y,
+		"rotation", &rotation, NULL);
+	ld_diagram_view_diagram_to_widget_coords (data->self, x, y, &x, &y);
+	cairo_translate (data->cr, x, y);
+	cairo_scale (data->cr, data->scale, data->scale);
+
+	switch (rotation)
+	{
+	case LD_DIAGRAM_SYMBOL_ROTATION_90:
+		cairo_rotate (data->cr, G_PI * 0.5);
+		break;
+	case LD_DIAGRAM_SYMBOL_ROTATION_180:
+		cairo_rotate (data->cr, G_PI);
+		break;
+	case LD_DIAGRAM_SYMBOL_ROTATION_270:
+		cairo_rotate (data->cr, G_PI * 1.5);
+		break;
+	}
+
+	ld_symbol_draw (symbol, data->cr);
+	cairo_restore (data->cr);
+}
+
+static void
+draw_connection (LdDiagramConnection *connection, DrawData *data)
+{
+	LdRectangle clip_rect;
+	LdPointArray *points;
+	gdouble x, y;
+	guint i;
+
+	if (!get_connection_clip_area (data->self, connection, &clip_rect)
+		|| !ld_rectangle_intersects (&clip_rect, &data->exposed_rect))
+		return;
+
+	points = ld_diagram_connection_get_points (connection);
+	if (points->length < 2)
+		goto draw_connection_end;
+
+	cairo_save (data->cr);
+
+	g_object_get (connection, "x", &x, "y", &y, NULL);
+	ld_diagram_view_diagram_to_widget_coords (data->self, x, y, &x, &y);
+	cairo_translate (data->cr, x, y);
+	cairo_scale (data->cr, data->scale, data->scale);
+
+	for (i = 1; i < points->length; i++)
+	{
+		cairo_move_to (data->cr,
+			points->points[i - 1].x,
+			points->points[i - 1].y);
+		cairo_line_to (data->cr,
+			points->points[i].x,
+			points->points[i].y);
+		cairo_stroke (data->cr);
+	}
+	cairo_restore (data->cr);
+
+draw_connection_end:
+	ld_point_array_free (points);
+	return;
+}