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+//
+// fastiv-view.c: fast image viewer - view widget
+//
+// Copyright (c) 2021, Přemysl Eric Janouch <p@janouch.name>
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
+// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+//
+
+#define WUFFS_IMPLEMENTATION
+#define WUFFS_CONFIG__MODULES
+#define WUFFS_CONFIG__MODULE__ADLER32
+#define WUFFS_CONFIG__MODULE__BASE
+#define WUFFS_CONFIG__MODULE__BMP
+#define WUFFS_CONFIG__MODULE__CRC32
+#define WUFFS_CONFIG__MODULE__DEFLATE
+#define WUFFS_CONFIG__MODULE__GIF
+#define WUFFS_CONFIG__MODULE__LZW
+#define WUFFS_CONFIG__MODULE__PNG
+#define WUFFS_CONFIG__MODULE__ZLIB
+
+#include "wuffs-mirror-release-c/release/c/wuffs-v0.3.c"
+#include <turbojpeg.h>
+
+#include "fastiv-view.h"
+
+struct _FastivView {
+	GtkWidget parent_instance;
+	cairo_surface_t *surface;
+	// TODO(p): Eventually, we'll want to have the zoom level (scale) here,
+	// and some zoom-to-fit indication.
+};
+
+G_DEFINE_TYPE(FastivView, fastiv_view, GTK_TYPE_WIDGET)
+
+static void
+fastiv_view_finalize(GObject *gobject)
+{
+	FastivView *self = FASTIV_VIEW(gobject);
+	cairo_surface_destroy(self->surface);
+
+	G_OBJECT_CLASS(fastiv_view_parent_class)->finalize(gobject);
+}
+
+static void
+fastiv_view_get_preferred_height(GtkWidget *widget,
+	gint *minimum, gint *natural)
+{
+	*minimum = 0;
+	*natural = 0;
+
+	// TODO(p): Times the zoom.
+	FastivView *self = FASTIV_VIEW(widget);
+	if (self->surface)
+		*natural = cairo_image_surface_get_height(self->surface);
+}
+
+static void
+fastiv_view_get_preferred_width(GtkWidget *widget,
+	gint *minimum, gint *natural)
+{
+	*minimum = 0;
+	*natural = 0;
+
+	// TODO(p): Times the zoom.
+	FastivView *self = FASTIV_VIEW(widget);
+	if (self->surface)
+		*natural = cairo_image_surface_get_width(self->surface);
+}
+
+static gboolean
+fastiv_view_draw(GtkWidget *widget, cairo_t *cr)
+{
+	FastivView *self = FASTIV_VIEW(widget);
+	if (!self->surface)
+		return TRUE;
+
+	// TODO(p): Times the zoom.
+	cairo_set_source_surface(cr, self->surface, 0, 0);
+	cairo_paint(cr);
+	return TRUE;
+}
+
+static void
+fastiv_view_class_init(FastivViewClass *klass)
+{
+	GObjectClass *object_class = G_OBJECT_CLASS(klass);
+	object_class->finalize = fastiv_view_finalize;
+
+	GtkWidgetClass *widget_class = GTK_WIDGET_CLASS(klass);
+	widget_class->get_preferred_height = fastiv_view_get_preferred_height;
+	widget_class->get_preferred_width = fastiv_view_get_preferred_width;
+	widget_class->draw = fastiv_view_draw;
+}
+
+static void
+fastiv_view_init(FastivView *self)
+{
+	gtk_widget_set_has_window(GTK_WIDGET(self), FALSE);
+}
+
+// --- Picture loading ---------------------------------------------------------
+
+#define FASTIV_VIEW_ERROR  fastiv_view_error_quark()
+
+G_DEFINE_QUARK(fastiv-view-error-quark, fastiv_view_error)
+
+enum FastivViewError {
+	FASTIV_VIEW_ERROR_OPEN,
+};
+
+static void
+set_error(GError **error, const char *message)
+{
+	g_set_error_literal(error,
+		FASTIV_VIEW_ERROR, FASTIV_VIEW_ERROR_OPEN, message);
+}
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+// https://github.com/google/wuffs/blob/main/example/gifplayer/gifplayer.c
+// is pure C, and a good reference. I can't use the auxiliary libraries,
+// since they depend on C++, which is undesirable.
+static cairo_surface_t *
+open_wuffs(wuffs_base__image_decoder *dec,
+	wuffs_base__io_buffer src, GError **error)
+{
+	wuffs_base__image_config cfg;
+	wuffs_base__status status =
+		wuffs_base__image_decoder__decode_image_config(dec, &cfg, &src);
+	if (!wuffs_base__status__is_ok(&status)) {
+		set_error(error, wuffs_base__status__message(&status));
+		return NULL;
+	}
+	if (!wuffs_base__image_config__is_valid(&cfg)) {
+		set_error(error, "invalid Wuffs image configuration");
+		return NULL;
+	}
+
+	// We need to check because of the Cairo API.
+	uint32_t width = wuffs_base__pixel_config__width(&cfg.pixcfg);
+    uint32_t height = wuffs_base__pixel_config__height(&cfg.pixcfg);
+	if (width > INT_MAX || height > INT_MAX) {
+		set_error(error, "image dimensions overflow");
+		return NULL;
+	}
+
+	// CAIRO_FORMAT_ARGB32: "The 32-bit quantities are stored native-endian.
+	//   Pre-multiplied alpha is used."
+	// CAIRO_FORMAT_RGB{24,30}: analogous, not going to use these so far.
+	//
+	// Wuffs: /doc/note/pixel-formats.md specifies it as "memory order", which,
+	// for our purposes, means big endian.  Currently useful formats, as per
+	// support within wuffs_base__pixel_swizzler__prepare__*():
+	//  - WUFFS_BASE__PIXEL_FORMAT__ARGB_PREMUL: big-endian
+	//  - WUFFS_BASE__PIXEL_FORMAT__BGRA_PREMUL: little-endian
+	//  - WUFFS_BASE__PIXEL_FORMAT__XRGB: big-endian
+	//  - WUFFS_BASE__PIXEL_FORMAT__BGRX: little-endian
+	//
+	// TODO(p): Make Wuffs support RGB30 as a destination format,
+	// so far we only have WUFFS_BASE__PIXEL_FORMAT__BGRA_NONPREMUL_4X16LE
+	// and in general, 16-bit depth swizzlers are stubbed.
+	wuffs_base__pixel_config__set(&cfg.pixcfg,
+#if G_BYTE_ORDER == G_LITTLE_ENDIAN
+		WUFFS_BASE__PIXEL_FORMAT__BGRA_PREMUL,
+#else
+		WUFFS_BASE__PIXEL_FORMAT__ARGB_PREMUL,
+#endif
+		WUFFS_BASE__PIXEL_SUBSAMPLING__NONE, width, height);
+
+	wuffs_base__slice_u8 workbuf = {0};
+	uint64_t workbuf_len_max_incl =
+		wuffs_base__image_decoder__workbuf_len(dec).max_incl;
+	if (workbuf_len_max_incl) {
+		workbuf = wuffs_base__malloc_slice_u8(malloc, workbuf_len_max_incl);
+		if (!workbuf.ptr) {
+			set_error(error, "failed to allocate a work buffer");
+			return NULL;
+		}
+	}
+
+	cairo_surface_t *surface =
+		cairo_image_surface_create(CAIRO_FORMAT_ARGB32, width, height);
+	if (!surface) {
+		set_error(error, "failed to allocate an image surface");
+		free(workbuf.ptr);
+		return NULL;
+	}
+
+	// CAIRO_STRIDE_ALIGNMENT is 4 bytes, so there will be no padding with
+	// ARGB/BGR/XRGB/BGRX.  This function does not support a stride different
+	// from the width, maybe Wuffs internals do not either.
+	wuffs_base__pixel_buffer pb = {0};
+	status = wuffs_base__pixel_buffer__set_from_slice(&pb, &cfg.pixcfg,
+		wuffs_base__make_slice_u8(cairo_image_surface_get_data(surface),
+			cairo_image_surface_get_stride(surface) *
+			cairo_image_surface_get_height(surface)));
+	if (!wuffs_base__status__is_ok(&status)) {
+		set_error(error, wuffs_base__status__message(&status));
+		cairo_surface_destroy(surface);
+		free(workbuf.ptr);
+		return NULL;
+	}
+
+#if 0  // We're not using this right now.
+	wuffs_base__frame_config fc = {0};
+	status = wuffs_png__decoder__decode_frame_config(&dec, &fc, &src);
+	if (!wuffs_base__status__is_ok(&status)) {
+		set_error(error, wuffs_base__status__message(&status));
+		cairo_surface_destroy(surface);
+		free(workbuf.ptr);
+		return NULL;
+	}
+#endif
+
+	// Starting to modify pixel data directly. Probably an unnecessary call.
+	cairo_surface_flush(surface);
+
+	status = wuffs_base__image_decoder__decode_frame(dec, &pb, &src,
+		WUFFS_BASE__PIXEL_BLEND__SRC, workbuf, NULL);
+	if (!wuffs_base__status__is_ok(&status)) {
+		set_error(error, wuffs_base__status__message(&status));
+		cairo_surface_destroy(surface);
+		free(workbuf.ptr);
+		return NULL;
+	}
+
+	// Pixel data has been written, need to let Cairo know.
+	cairo_surface_mark_dirty(surface);
+
+	free(workbuf.ptr);
+	return surface;
+}
+
+static cairo_surface_t *
+open_wuffs_using(wuffs_base__image_decoder *(*allocate)(),
+	const gchar *data, gsize len, GError **error)
+{
+	wuffs_base__image_decoder *dec = allocate();
+	if (!dec) {
+		set_error(error, "memory allocation failed or internal error");
+		return NULL;
+	}
+
+	cairo_surface_t *surface = open_wuffs(dec,
+		wuffs_base__ptr_u8__reader((uint8_t *) data, len, TRUE), error);
+	free(dec);
+	return surface;
+}
+
+static void
+trivial_cmyk_to_bgra(unsigned char *p, int len)
+{
+	// Inspired by gdk-pixbuf's io-jpeg.c:
+	//
+	// Assume that all YCCK/CMYK JPEG files use inverted CMYK, as Photoshop
+	// does, see https://bugzilla.gnome.org/show_bug.cgi?id=618096
+	while (len--) {
+		int c = p[0], m = p[1], y = p[2], k = p[3];
+		p[0] = k * y / 255;
+		p[1] = k * m / 255;
+		p[2] = k * c / 255;
+		p[3] = 255;
+		p += 4;
+	}
+}
+
+static cairo_surface_t *
+open_libjpeg_turbo(const gchar *data, gsize len, GError **error)
+{
+	tjhandle dec = tjInitDecompress();
+	if (!dec) {
+		set_error(error, tjGetErrorStr2(dec));
+		return NULL;
+	}
+
+	int width = 0, height = 0, subsampling = TJSAMP_444, colorspace = TJCS_RGB;
+	if (tjDecompressHeader3(dec, (const unsigned char *) data, len,
+			&width, &height, &subsampling, &colorspace)) {
+		set_error(error, tjGetErrorStr2(dec));
+		tjDestroy(dec);
+		return NULL;
+	}
+
+	int pixel_format = (colorspace == TJCS_CMYK || colorspace == TJCS_YCCK)
+		? TJPF_CMYK
+		: (G_BYTE_ORDER == G_LITTLE_ENDIAN ? TJPF_BGRA : TJPF_ARGB);
+
+	cairo_surface_t *surface =
+		cairo_image_surface_create(CAIRO_FORMAT_ARGB32, width, height);
+	if (!surface) {
+		set_error(error, "failed to allocate an image surface");
+		tjDestroy(dec);
+		return NULL;
+	}
+
+	// Starting to modify pixel data directly. Probably an unnecessary call.
+	cairo_surface_flush(surface);
+
+	int stride = cairo_image_surface_get_stride(surface);
+	if (tjDecompress2(dec, (const unsigned char *) data, len,
+			cairo_image_surface_get_data(surface), width, stride,
+			height, pixel_format, TJFLAG_ACCURATEDCT)) {
+		set_error(error, tjGetErrorStr2(dec));
+		cairo_surface_destroy(surface);
+		tjDestroy(dec);
+		return NULL;
+	}
+
+	// TODO(p): Support big-endian machines, too, those need ARGB ordering.
+	if (pixel_format == TJPF_CMYK) {
+		// CAIRO_STRIDE_ALIGNMENT is 4 bytes, so there will be no padding with
+		// ARGB/BGR/XRGB/BGRX.
+		trivial_cmyk_to_bgra(cairo_image_surface_get_data(surface),
+			width * height);
+	}
+
+	// Pixel data has been written, need to let Cairo know.
+	cairo_surface_mark_dirty(surface);
+
+	tjDestroy(dec);
+	return surface;
+}
+
+// TODO(p): Progressive picture loading, or at least async/cancellable.
+gboolean
+fastiv_view_open(FastivView *self, const gchar *path, GError **error)
+{
+	// TODO(p): Don't always load everything into memory, test type first,
+	// for which we only need the first 16 bytes right now.
+	gchar *data = NULL;
+	gsize len = 0;
+	if (!g_file_get_contents(path, &data, &len, error))
+		return FALSE;
+
+	wuffs_base__slice_u8 prefix =
+		wuffs_base__make_slice_u8((uint8_t *) data, len);
+
+	cairo_surface_t *surface = NULL;
+	switch (wuffs_base__magic_number_guess_fourcc(prefix)) {
+	case WUFFS_BASE__FOURCC__BMP:
+		// Note that BMP can redirect into another format, which is unsupported.
+		surface = open_wuffs_using(
+			wuffs_bmp__decoder__alloc_as__wuffs_base__image_decoder,
+			data, len, error);
+		break;
+	case WUFFS_BASE__FOURCC__GIF:
+		surface = open_wuffs_using(
+			wuffs_gif__decoder__alloc_as__wuffs_base__image_decoder,
+			data, len, error);
+		break;
+	case WUFFS_BASE__FOURCC__PNG:
+		surface = open_wuffs_using(
+			wuffs_png__decoder__alloc_as__wuffs_base__image_decoder,
+			data, len, error);
+		break;
+	case WUFFS_BASE__FOURCC__JPEG:
+		surface = open_libjpeg_turbo(data, len, error);
+		break;
+	default:
+		// TODO(p): Integrate gdk-pixbuf as a fallback (optional dependency).
+		set_error(error, "unsupported file type");
+	}
+
+	free(data);
+	if (!surface)
+		return FALSE;
+
+	if (self->surface)
+		cairo_surface_destroy(self->surface);
+
+	self->surface = surface;
+	gtk_widget_queue_resize(GTK_WIDGET(self));
+	return TRUE;
+}