Split out image loaders into fastiv-io.c

4 files changed, 432 insertions, 402 deletions

diff --git a/fastiv-io.c b/fastiv-io.c
new file mode 100644
index 0000000..25b99b2
--- /dev/null
+++ b/fastiv-io.c
@@ -0,0 +1,426 @@
+//
+// fastiv-io.c: image loaders
+//
+// 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.
+//
+
+#include "config.h"
+
+#include <glib.h>
+#include <cairo.h>
+#include <turbojpeg.h>
+#ifdef HAVE_LIBRAW
+#include <libraw.h>
+#endif  // HAVE_LIBRAW
+
+#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"
+
+// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
+
+#define FASTIV_IO_ERROR  fastiv_io_error_quark()
+
+G_DEFINE_QUARK(fastiv-io-error-quark, fastiv_io_error)
+
+enum FastivIoError {
+	FASTIV_IO_ERROR_OPEN,
+};
+
+static void
+set_error(GError **error, const char *message)
+{
+	g_set_error_literal(error,
+		FASTIV_IO_ERROR, FASTIV_IO_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);
+	cairo_status_t surface_status = cairo_surface_status(surface);
+	if (surface_status != CAIRO_STATUS_SUCCESS) {
+		set_error(error, cairo_status_to_string(surface_status));
+		cairo_surface_destroy(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);
+	cairo_status_t surface_status = cairo_surface_status(surface);
+	if (surface_status != CAIRO_STATUS_SUCCESS) {
+		set_error(error, cairo_status_to_string(surface_status));
+		cairo_surface_destroy(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;
+}
+
+#ifdef HAVE_LIBRAW  // ---------------------------------------------------------
+
+static cairo_surface_t *
+open_libraw(const gchar *data, gsize len, GError **error)
+{
+	// https://github.com/LibRaw/LibRaw/issues/418
+	libraw_data_t *iprc = libraw_init(LIBRAW_OPIONS_NO_MEMERR_CALLBACK
+		| LIBRAW_OPIONS_NO_DATAERR_CALLBACK);
+	if (!iprc) {
+		set_error(error, "failed to obtain a LibRaw handle");
+		return NULL;
+	}
+
+#if 0
+	// TODO(p): Consider setting this--the image is still likely to be
+	// rendered suboptimally, so why not make it faster.
+	iprc->params.half_size = 1;
+#endif
+
+	// TODO(p): Check if we need to set anything for autorotation (sizes.flip).
+	iprc->params.use_camera_wb = 1;
+	iprc->params.output_color = 1;  // sRGB, TODO(p): Is this used?
+	iprc->params.output_bps = 8;  // This should be the default value.
+
+	int err = 0;
+	if ((err = libraw_open_buffer(iprc, (void *) data, len))) {
+		set_error(error, libraw_strerror(err));
+		libraw_close(iprc);
+		return NULL;
+	}
+
+	// TODO(p): Do we need to check iprc->idata.raw_count? Maybe for TIFFs?
+	if ((err = libraw_unpack(iprc))) {
+		set_error(error, libraw_strerror(err));
+		libraw_close(iprc);
+		return NULL;
+	}
+
+#if 0
+	// TODO(p): I'm not sure when this is necessary or useful yet.
+	if ((err = libraw_adjust_sizes_info_only(iprc))) {
+		set_error(error, libraw_strerror(err));
+		libraw_close(iprc);
+		return NULL;
+	}
+#endif
+
+	// TODO(p): Documentation says I should look at the code and do it myself.
+	if ((err = libraw_dcraw_process(iprc))) {
+		set_error(error, libraw_strerror(err));
+		libraw_close(iprc);
+		return NULL;
+	}
+
+	// FIXME: This is shittily written to iterate over the range of
+	// idata.colors, and will be naturally slow.
+	libraw_processed_image_t *image = libraw_dcraw_make_mem_image(iprc, &err);
+	if (!image) {
+		set_error(error, libraw_strerror(err));
+		libraw_close(iprc);
+		return NULL;
+	}
+
+	// This should have been transformed, and kept, respectively.
+	if (image->colors != 3 || image->bits != 8) {
+		set_error(error, "unexpected number of colours, or bit depth");
+		libraw_dcraw_clear_mem(image);
+		libraw_close(iprc);
+		return NULL;
+	}
+
+	int width = image->width, height = image->height;
+	cairo_surface_t *surface =
+		cairo_image_surface_create(CAIRO_FORMAT_ARGB32, width, height);
+	cairo_status_t surface_status = cairo_surface_status(surface);
+	if (surface_status != CAIRO_STATUS_SUCCESS) {
+		set_error(error, cairo_status_to_string(surface_status));
+		cairo_surface_destroy(surface);
+		libraw_dcraw_clear_mem(image);
+		libraw_close(iprc);
+		return NULL;
+	}
+
+	// Starting to modify pixel data directly. Probably an unnecessary call.
+	cairo_surface_flush(surface);
+
+	uint32_t *pixels = (uint32_t *) cairo_image_surface_get_data(surface);
+	unsigned char *p = image->data;
+	for (ushort y = 0; y < image->height; y++) {
+		for (ushort x = 0; x < image->width; x++) {
+			*pixels++ = 0xff000000 | (uint32_t) p[0] << 16
+				| (uint32_t) p[1] << 8 | (uint32_t) p[2];
+			p += 3;
+		}
+	}
+
+	// Pixel data has been written, need to let Cairo know.
+	cairo_surface_mark_dirty(surface);
+
+	libraw_dcraw_clear_mem(image);
+	libraw_close(iprc);
+	return surface;
+}
+
+#endif  // HAVE_LIBRAW ---------------------------------------------------------
+
+cairo_surface_t *
+fastiv_io_open(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.
+	// Though LibRaw poses an issue--we may want to try to map RAW formats
+	// to FourCC values--many of them are compliant TIFF files.
+	// We might want to employ a more generic way of magic identification,
+	// and with some luck, it could even be integrated into Wuffs.
+	gchar *data = NULL;
+	gsize len = 0;
+	if (!g_file_get_contents(path, &data, &len, error))
+		return NULL;
+
+	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:
+#ifdef HAVE_LIBRAW  // ---------------------------------------------------------
+		if ((surface = open_libraw(data, len, error)))
+			break;
+
+		// TODO(p): We should try to pass actual processing errors through,
+		// notably only continue with LIBRAW_FILE_UNSUPPORTED.
+		g_clear_error(error);
+#endif  // HAVE_LIBRAW ---------------------------------------------------------
+
+		// TODO(p): Integrate gdk-pixbuf as a fallback (optional dependency).
+		set_error(error, "unsupported file type");
+	}
+	free(data);
+	return surface;
+}
diff --git a/fastiv-view.c b/fastiv-view.c
index a7bf0cd..9d00e63 100644
--- a/fastiv-view.c
+++ b/fastiv-view.c
@@ -15,28 +15,10 @@
 // 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 <math.h>
 
-#include "wuffs-mirror-release-c/release/c/wuffs-v0.3.c"
-#include <turbojpeg.h>
-
-#include "config.h"
 #include "fastiv-view.h"
 
-#ifdef HAVE_LIBRAW
-#include <libraw.h>
-#endif  // HAVE_LIBRAW
-
 struct _FastivView {
 	GtkWidget parent_instance;
 	cairo_surface_t *surface;
@@ -149,394 +131,13 @@ fastiv_view_init(FastivView *self)
 
 // --- 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);
-	cairo_status_t surface_status = cairo_surface_status(surface);
-	if (surface_status != CAIRO_STATUS_SUCCESS) {
-		set_error(error, cairo_status_to_string(surface_status));
-		cairo_surface_destroy(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);
-	cairo_status_t surface_status = cairo_surface_status(surface);
-	if (surface_status != CAIRO_STATUS_SUCCESS) {
-		set_error(error, cairo_status_to_string(surface_status));
-		cairo_surface_destroy(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;
-}
-
-#ifdef HAVE_LIBRAW  // ---------------------------------------------------------
-
-static cairo_surface_t *
-open_libraw(const gchar *data, gsize len, GError **error)
-{
-	// https://github.com/LibRaw/LibRaw/issues/418
-	libraw_data_t *iprc = libraw_init(LIBRAW_OPIONS_NO_MEMERR_CALLBACK
-		| LIBRAW_OPIONS_NO_DATAERR_CALLBACK);
-	if (!iprc) {
-		set_error(error, "failed to obtain a LibRaw handle");
-		return NULL;
-	}
-
-#if 0
-	// TODO(p): Consider setting this--the image is still likely to be
-	// rendered suboptimally, so why not make it faster.
-	iprc->params.half_size = 1;
-#endif
-
-	// TODO(p): Check if we need to set anything for autorotation (sizes.flip).
-	iprc->params.use_camera_wb = 1;
-	iprc->params.output_color = 1;  // sRGB, TODO(p): Is this used?
-	iprc->params.output_bps = 8;  // This should be the default value.
-
-	int err = 0;
-	if ((err = libraw_open_buffer(iprc, (void *) data, len))) {
-		set_error(error, libraw_strerror(err));
-		libraw_close(iprc);
-		return NULL;
-	}
-
-	// TODO(p): Do we need to check iprc->idata.raw_count? Maybe for TIFFs?
-	if ((err = libraw_unpack(iprc))) {
-		set_error(error, libraw_strerror(err));
-		libraw_close(iprc);
-		return NULL;
-	}
-
-#if 0
-	// TODO(p): I'm not sure when this is necessary or useful yet.
-	if ((err = libraw_adjust_sizes_info_only(iprc))) {
-		set_error(error, libraw_strerror(err));
-		libraw_close(iprc);
-		return NULL;
-	}
-#endif
-
-	// TODO(p): Documentation says I should look at the code and do it myself.
-	if ((err = libraw_dcraw_process(iprc))) {
-		set_error(error, libraw_strerror(err));
-		libraw_close(iprc);
-		return NULL;
-	}
-
-	// FIXME: This is shittily written to iterate over the range of
-	// idata.colors, and will be naturally slow.
-	libraw_processed_image_t *image = libraw_dcraw_make_mem_image(iprc, &err);
-	if (!image) {
-		set_error(error, libraw_strerror(err));
-		libraw_close(iprc);
-		return NULL;
-	}
-
-	// This should have been transformed, and kept, respectively.
-	if (image->colors != 3 || image->bits != 8) {
-		set_error(error, "unexpected number of colours, or bit depth");
-		libraw_dcraw_clear_mem(image);
-		libraw_close(iprc);
-		return NULL;
-	}
-
-	int width = image->width, height = image->height;
-	cairo_surface_t *surface =
-		cairo_image_surface_create(CAIRO_FORMAT_ARGB32, width, height);
-	cairo_status_t surface_status = cairo_surface_status(surface);
-	if (surface_status != CAIRO_STATUS_SUCCESS) {
-		set_error(error, cairo_status_to_string(surface_status));
-		cairo_surface_destroy(surface);
-		libraw_dcraw_clear_mem(image);
-		libraw_close(iprc);
-		return NULL;
-	}
-
-	// Starting to modify pixel data directly. Probably an unnecessary call.
-	cairo_surface_flush(surface);
-
-	uint32_t *pixels = (uint32_t *) cairo_image_surface_get_data(surface);
-	unsigned char *p = image->data;
-	for (ushort y = 0; y < image->height; y++) {
-		for (ushort x = 0; x < image->width; x++) {
-			*pixels++ = 0xff000000 | (uint32_t) p[0] << 16
-				| (uint32_t) p[1] << 8 | (uint32_t) p[2];
-			p += 3;
-		}
-	}
-
-	// Pixel data has been written, need to let Cairo know.
-	cairo_surface_mark_dirty(surface);
-
-	libraw_dcraw_clear_mem(image);
-	libraw_close(iprc);
-	return surface;
-}
-
-#endif  // HAVE_LIBRAW ---------------------------------------------------------
-
 // 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.
-	// Though LibRaw poses an issue--we may want to try to map RAW formats
-	// to FourCC values--many of them are compliant TIFF files.
-	// We might want to employ a more generic way of magic identification,
-	// and with some luck, it could even be integrated into Wuffs.
-	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:
-#ifdef HAVE_LIBRAW  // ---------------------------------------------------------
-		if ((surface = open_libraw(data, len, error)))
-			break;
-
-		// TODO(p): We should try to pass actual processing errors through,
-		// notably only continue with LIBRAW_FILE_UNSUPPORTED.
-		g_clear_error(error);
-#endif  // HAVE_LIBRAW ---------------------------------------------------------
-
-		// TODO(p): Integrate gdk-pixbuf as a fallback (optional dependency).
-		set_error(error, "unsupported file type");
-	}
-
-	free(data);
+	cairo_surface_t *surface = fastiv_io_open(path, error);
 	if (!surface)
 		return FALSE;
-
 	if (self->surface)
 		cairo_surface_destroy(self->surface);
 
diff --git a/fastiv-view.h b/fastiv-view.h
index ed9260c..d9cfdba 100644
--- a/fastiv-view.h
+++ b/fastiv-view.h
@@ -24,3 +24,6 @@ G_DECLARE_FINAL_TYPE(FastivView, fastiv_view, FASTIV, VIEW, GtkWidget)
 
 /// Try to open the given file, synchronously, to be displayed by the widget.
 gboolean fastiv_view_open(FastivView *self, const gchar *path, GError **error);
+
+// Private, fastiv-io.c
+cairo_surface_t *fastiv_io_open(const gchar *path, GError **error);
diff --git a/meson.build b/meson.build
index 8c97696..deb6b46 100644
--- a/meson.build
+++ b/meson.build
@@ -18,7 +18,7 @@ configure_file(
 	configuration : conf,
 )
 
-executable('fastiv', 'fastiv.c', 'fastiv-view.c',
+executable('fastiv', 'fastiv.c', 'fastiv-view.c', 'fastiv-io.c',
 	install : true,
 	dependencies : [dependencies])