thumbnailer: Add an external thumbnailer for images

So that broken images, or images that use too much RAM can get killed
without prejudice.

_gdk_pixbuf_new_from_uri_at_scale() and
gnome_desktop_thumbnail_scale_down_pixbuf () are directly from
gnome-desktop.

https://bugzilla.gnome.org/show_bug.cgi?id=768062

Makefile.am

-SUBDIRS = gdk-pixbuf po docs tests contrib build
+SUBDIRS = gdk-pixbuf po docs thumbnailer tests contrib build
 
 EXTRA_DIST = 			\
 	config.h.win32 		\

configure.ac

@@ -1121,6 +1121,7 @@ docs/reference/gdk-pixbuf/Makefile
 docs/reference/gdk-pixbuf/version.xml
 po/Makefile.in
 tests/Makefile
+thumbnailer/Makefile
 contrib/Makefile
 contrib/gdk-pixbuf-xlib/Makefile
 contrib/gdk-pixbuf-xlib/gdk-pixbuf-xlib-2.0.pc

thumbnailer/Makefile.am

+bin_PROGRAMS = gdk-pixbuf-thumbnailer
+noinst_PROGRAMS = gdk-pixbuf-print-mime-types
+
+gdk_pixbuf_thumbnailer_SOURCES = gdk-pixbuf-thumbnailer.c gnome-thumbnailer-skeleton.c gnome-thumbnailer-skeleton.h
+gdk_pixbuf_thumbnailer_CPPFLAGS =			\
+	-I$(top_srcdir)					\
+	-I$(top_srcdir)/gdk-pixbuf			\
+	$(GDK_PIXBUF_DEP_CFLAGS)			\
+	-DTHUMBNAILER_RETURNS_PIXBUF			\
+	-DTHUMBNAILER_USAGE="\"Thumbnail images\""	\
+	$(WARN_CFLAGS)
+gdk_pixbuf_thumbnailer_LDADD =				\
+	$(GDK_PIXBUF_DEP_LIBS)				\
+	$(top_builddir)/gdk-pixbuf/libgdk_pixbuf-$(GDK_PIXBUF_API_VERSION).la
+
+gdk_pixbuf_print_mime_types_SOURCES = gdk-pixbuf-print-mime-types.c
+gdk_pixbuf_print_mime_types_CPPFLAGS =			\
+	-I$(top_srcdir)					\
+	-I$(top_srcdir)/gdk-pixbuf			\
+	$(GDK_PIXBUF_DEP_CFLAGS)			\
+	$(WARN_CFLAGS)
+gdk_pixbuf_print_mime_types_LDADD =			\
+	$(GDK_PIXBUF_DEP_LIBS)				\
+	$(top_builddir)/gdk-pixbuf/libgdk_pixbuf-$(GDK_PIXBUF_API_VERSION).la
+
+thumbnailerdir = $(datadir)/thumbnailers/
+thumbnailer_DATA = gdk-pixbuf-thumbnailer.thumbnailer
+gdk-pixbuf-thumbnailer.thumbnailer: gdk-pixbuf-thumbnailer.thumbnailer.in Makefile gdk-pixbuf-print-mime-types
+	$(AM_V_GEN) GDK_PIXBUF_MODULE_FILE=$(top_builddir)/gdk-pixbuf/loaders.cache	\
+	GDK_PIXBUF_PIXDATA=$(top_builddir)/gdk-pixbuf/gdk-pixbuf-pixdata		\
+	$(SED) -e "s|\@bindir\@|$(bindir)|"						\
+	-e "s|\@mimetypes\@|`$(builddir)/gdk-pixbuf-print-mime-types`|" $< > $@
+
+EXTRA_DIST = gdk-pixbuf-thumbnailer.thumbnailer.in
+
+CLEANFILES = $(thumbnailer_DATA)

thumbnailer/gdk-pixbuf-print-mime-types.c

+#include <gdk-pixbuf/gdk-pixbuf.h>
+
+int main (int argc, char **argv)
+{
+	GSList *formats, *l;
+	GString *s;
+
+	formats = gdk_pixbuf_get_formats ();
+	s = g_string_new (NULL);
+	for (l = formats; l != NULL; l = l->next) {
+		GdkPixbufFormat *format = l->data;
+		char **mime_types;
+		guint i;
+
+		mime_types = gdk_pixbuf_format_get_mime_types (format);
+		for (i = 0; mime_types[i] != NULL; i++) {
+			g_string_append (s, mime_types[i]);
+			g_string_append (s, ";");
+		}
+
+		g_strfreev (mime_types);
+	}
+	g_slist_free (formats);
+
+	g_print ("%s", s->str);
+	g_string_free (s, TRUE);
+
+	return 0;
+}

thumbnailer/gdk-pixbuf-thumbnailer.c

+/*
+ * Copyright (C) 2016 Bastien Nocera <hadess@hadess.net>
+ *
+ * Authors: Bastien Nocera <hadess@hadess.net>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ *
+ */
+
+#include <string.h>
+#include <glib.h>
+
+#include "gnome-thumbnailer-skeleton.h"
+
+typedef struct {
+    gint width;
+    gint height;
+    gint input_width;
+    gint input_height;
+    gboolean preserve_aspect_ratio;
+} SizePrepareContext;
+
+#define LOAD_BUFFER_SIZE 4096
+
+static void
+size_prepared_cb (GdkPixbufLoader *loader, 
+		  int              width,
+		  int              height,
+		  gpointer         data)
+{
+  SizePrepareContext *info = data;
+  
+  g_return_if_fail (width > 0 && height > 0);
+  
+  info->input_width = width;
+  info->input_height = height;
+  
+  if (width < info->width && height < info->height) return;
+  
+  if (info->preserve_aspect_ratio && 
+      (info->width > 0 || info->height > 0)) {
+    if (info->width < 0)
+      {
+	width = width * (double)info->height/(double)height;
+	height = info->height;
+      }
+    else if (info->height < 0)
+      {
+	height = height * (double)info->width/(double)width;
+	width = info->width;
+      }
+    else if ((double)height * (double)info->width >
+	     (double)width * (double)info->height) {
+      width = 0.5 + (double)width * (double)info->height / (double)height;
+      height = info->height;
+    } else {
+      height = 0.5 + (double)height * (double)info->width / (double)width;
+      width = info->width;
+    }
+  } else {
+    if (info->width > 0)
+      width = info->width;
+    if (info->height > 0)
+      height = info->height;
+  }
+  
+  gdk_pixbuf_loader_set_size (loader, width, height);
+}
+
+static GdkPixbufLoader *
+create_loader (GFile        *file,
+               const guchar *data,
+               gsize         size)
+{
+  GdkPixbufLoader *loader;
+  GError *error = NULL;
+  char *mime_type;
+  char *filename;
+
+  loader = NULL;
+
+  /* need to specify the type here because the gdk_pixbuf_loader_write
+     doesn't have access to the filename in order to correct detect
+     the image type. */
+  filename = g_file_get_basename (file);
+  mime_type = g_content_type_guess (filename, data, size, NULL);
+  g_free (filename);
+
+  if (mime_type != NULL) {
+    loader = gdk_pixbuf_loader_new_with_mime_type (mime_type, &error);
+  }
+
+  if (loader == NULL) {
+    g_debug ("Unable to create loader for mime type %s: %s", mime_type, error->message);
+    g_clear_error (&error);
+    loader = gdk_pixbuf_loader_new ();
+  }
+  g_free (mime_type);
+
+  return loader;
+}
+
+static GdkPixbuf *
+_gdk_pixbuf_new_from_uri_at_scale (const char *uri,
+				   gint        width,
+				   gint        height,
+				   gboolean    preserve_aspect_ratio)
+{
+    gboolean result;
+    guchar buffer[LOAD_BUFFER_SIZE];
+    gssize bytes_read;
+    GdkPixbufLoader *loader = NULL;
+    GdkPixbuf *pixbuf;	
+    GdkPixbufAnimation *animation;
+    GdkPixbufAnimationIter *iter;
+    gboolean has_frame;
+    SizePrepareContext info;
+    GFile *file;
+    GFileInfo *file_info;
+    GInputStream *input_stream;
+    GError *error = NULL;
+
+    g_return_val_if_fail (uri != NULL, NULL);
+
+    input_stream = NULL;
+
+    file = g_file_new_for_uri (uri);
+
+    /* First see if we can get an input stream via preview::icon  */
+    file_info = g_file_query_info (file,
+                                   G_FILE_ATTRIBUTE_PREVIEW_ICON,
+                                   G_FILE_QUERY_INFO_NONE,
+                                   NULL,  /* GCancellable */
+                                   NULL); /* return location for GError */
+    if (file_info != NULL) {
+        GObject *object;
+
+        object = g_file_info_get_attribute_object (file_info,
+                                                   G_FILE_ATTRIBUTE_PREVIEW_ICON);
+        if (object != NULL && G_IS_LOADABLE_ICON (object)) {
+            input_stream = g_loadable_icon_load (G_LOADABLE_ICON (object),
+                                                 0,     /* size */
+                                                 NULL,  /* return location for type */
+                                                 NULL,  /* GCancellable */
+                                                 NULL); /* return location for GError */
+        }
+        g_object_unref (file_info);
+    }
+
+    if (input_stream == NULL) {
+	    input_stream = G_INPUT_STREAM (g_file_read (file, NULL, &error));
+	    if (input_stream == NULL) {
+		    g_warning ("Unable to create an input stream for %s: %s", uri, error->message);
+		    g_clear_error (&error);
+		    g_object_unref (file);
+		    return NULL;
+	    }
+    }
+
+    has_frame = FALSE;
+
+    result = FALSE;
+    while (!has_frame) {
+
+	bytes_read = g_input_stream_read (input_stream,
+					  buffer,
+					  sizeof (buffer),
+					  NULL,
+					  &error);
+        if (bytes_read == -1) {
+            g_warning ("Error reading from %s: %s", uri, error->message);
+            g_clear_error (&error);
+            break;
+        }
+	result = TRUE;
+	if (bytes_read == 0) {
+	    break;
+	}
+
+        if (loader == NULL) {
+            loader = create_loader (file, buffer, bytes_read);
+            if (1 <= width || 1 <= height) {
+              info.width = width;
+              info.height = height;
+              info.input_width = info.input_height = 0;
+              info.preserve_aspect_ratio = preserve_aspect_ratio;
+              g_signal_connect (loader, "size-prepared", G_CALLBACK (size_prepared_cb), &info);
+            }
+            g_assert (loader != NULL);
+        }
+
+	if (!gdk_pixbuf_loader_write (loader,
+				      (unsigned char *)buffer,
+				      bytes_read,
+				      &error)) {
+            g_warning ("Error creating thumbnail for %s: %s", uri, error->message);
+            g_clear_error (&error);
+	    result = FALSE;
+	    break;
+	}
+
+	animation = gdk_pixbuf_loader_get_animation (loader);
+	if (animation) {
+		iter = gdk_pixbuf_animation_get_iter (animation, NULL);
+		if (!gdk_pixbuf_animation_iter_on_currently_loading_frame (iter)) {
+			has_frame = TRUE;
+		}
+		g_object_unref (iter);
+	}
+    }
+
+    if (loader == NULL) {
+        /* This can happen if the above loop was exited due to the
+         * g_input_stream_read() call failing. */
+        result = FALSE;
+    } else if (gdk_pixbuf_loader_close (loader, &error) == FALSE &&
+               !g_error_matches (error, GDK_PIXBUF_ERROR, GDK_PIXBUF_ERROR_INCOMPLETE_ANIMATION)) {
+        g_warning ("Error creating thumbnail for %s: %s", uri, error->message);
+        result = FALSE;
+    }
+    g_clear_error (&error);
+
+    if (!result) {
+        g_clear_object (&loader);
+	g_input_stream_close (input_stream, NULL, NULL);
+	g_object_unref (input_stream);
+	g_object_unref (file);
+	return NULL;
+    }
+
+    g_input_stream_close (input_stream, NULL, NULL);
+    g_object_unref (input_stream);
+    g_object_unref (file);
+
+    pixbuf = gdk_pixbuf_loader_get_pixbuf (loader);
+    if (pixbuf != NULL) {
+	g_object_ref (G_OBJECT (pixbuf));
+	g_object_set_data (G_OBJECT (pixbuf), "gnome-original-width",
+			   GINT_TO_POINTER (info.input_width));
+	g_object_set_data (G_OBJECT (pixbuf), "gnome-original-height",
+			   GINT_TO_POINTER (info.input_height));
+    }
+    g_object_unref (G_OBJECT (loader));
+
+    return pixbuf;
+}
+
+GdkPixbuf *
+file_to_pixbuf (const char  *path,
+		guint        destination_size,
+	        GError     **error)
+{
+	GdkPixbuf *pixbuf, *tmp_pixbuf;
+	GFile *file;
+	char *uri;
+	int original_width, original_height;
+
+	file = g_file_new_for_path (path);
+	uri = g_file_get_uri (file);
+	pixbuf = _gdk_pixbuf_new_from_uri_at_scale (uri, destination_size, destination_size, TRUE);
+	if (pixbuf == NULL) {
+		g_set_error_literal (error, G_IO_ERROR, G_IO_ERROR_FAILED,
+				     "Generic error");
+		return pixbuf;
+	}
+
+	tmp_pixbuf = gdk_pixbuf_apply_embedded_orientation (pixbuf);
+	gdk_pixbuf_copy_options (pixbuf, tmp_pixbuf);
+	gdk_pixbuf_remove_option (tmp_pixbuf, "orientation");
+	g_object_unref (pixbuf);
+	pixbuf = tmp_pixbuf;
+
+        original_width = GPOINTER_TO_INT (g_object_get_data (G_OBJECT (pixbuf),
+                                                             "gnome-original-width"));
+        original_height = GPOINTER_TO_INT (g_object_get_data (G_OBJECT (pixbuf),
+                                                              "gnome-original-height"));
+
+	if (original_width > 0 && original_height > 0) {
+		char *tmp;
+
+		tmp = g_strdup_printf ("%d", original_width);
+		gdk_pixbuf_set_option (pixbuf, "tEXt::Thumb::Image::Width", tmp);
+		g_free (tmp);
+
+		tmp = g_strdup_printf ("%d", original_height);
+		gdk_pixbuf_set_option (pixbuf, "tEXt::Thumb::Image::Height", tmp);
+		g_free (tmp);
+	}
+
+	return pixbuf;
+}

thumbnailer/gdk-pixbuf-thumbnailer.thumbnailer.in

+[Thumbnailer Entry]
+TryExec=@bindir@/gdk-pixbuf-thumbnailer
+Exec=@bindir@/gdk-pixbuf-thumbnailer -s %s %u %o
+MimeType=@mimetypes@

thumbnailer/gnome-thumbnailer-skeleton.c

+/*
+ * Copyright (C) 2013 Bastien Nocera <hadess@hadess.net>
+ *
+ * Authors: Bastien Nocera <hadess@hadess.net>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ *
+ */
+
+#include <string.h>
+#include <glib.h>
+#include <gio/gio.h>
+#include <gdk-pixbuf/gdk-pixbuf.h>
+
+#include <math.h>
+#include <stdlib.h>
+
+#include "gnome-thumbnailer-skeleton.h"
+
+#ifndef THUMBNAILER_USAGE
+#error "THUMBNAILER_USAGE must be set"
+#endif
+
+static int output_size = 256;
+static gboolean g_fatal_warnings = FALSE;
+static char **filenames = NULL;
+
+/**
+ * gnome_desktop_thumbnail_scale_down_pixbuf:
+ * @pixbuf: a #GdkPixbuf
+ * @dest_width: the desired new width
+ * @dest_height: the desired new height
+ *
+ * Scales the pixbuf to the desired size. This function
+ * is a lot faster than gdk-pixbuf when scaling down by
+ * large amounts.
+ *
+ * Return value: (transfer full): a scaled pixbuf
+ * 
+ * Since: 2.2
+ **/
+GdkPixbuf *
+gnome_desktop_thumbnail_scale_down_pixbuf (GdkPixbuf *pixbuf,
+					   int dest_width,
+					   int dest_height)
+{
+	int source_width, source_height;
+	int s_x1, s_y1, s_x2, s_y2;
+	int s_xfrac, s_yfrac;
+	int dx, dx_frac, dy, dy_frac;
+	div_t ddx, ddy;
+	int x, y;
+	int r, g, b, a;
+	int n_pixels;
+	gboolean has_alpha;
+	guchar *dest, *src, *xsrc, *src_pixels;
+	GdkPixbuf *dest_pixbuf;
+	int pixel_stride;
+	int source_rowstride, dest_rowstride;
+
+	if (dest_width == 0 || dest_height == 0) {
+		return NULL;
+	}
+	
+	source_width = gdk_pixbuf_get_width (pixbuf);
+	source_height = gdk_pixbuf_get_height (pixbuf);
+
+	g_assert (source_width >= dest_width);
+	g_assert (source_height >= dest_height);
+
+	ddx = div (source_width, dest_width);
+	dx = ddx.quot;
+	dx_frac = ddx.rem;
+	
+	ddy = div (source_height, dest_height);
+	dy = ddy.quot;
+	dy_frac = ddy.rem;
+
+	has_alpha = gdk_pixbuf_get_has_alpha (pixbuf);
+	source_rowstride = gdk_pixbuf_get_rowstride (pixbuf);
+	src_pixels = gdk_pixbuf_get_pixels (pixbuf);
+
+	dest_pixbuf = gdk_pixbuf_new (GDK_COLORSPACE_RGB, has_alpha, 8,
+				      dest_width, dest_height);
+	dest = gdk_pixbuf_get_pixels (dest_pixbuf);
+	dest_rowstride = gdk_pixbuf_get_rowstride (dest_pixbuf);
+
+	pixel_stride = (has_alpha)?4:3;
+	
+	s_y1 = 0;
+	s_yfrac = -dest_height/2;
+	while (s_y1 < source_height) {
+		s_y2 = s_y1 + dy;
+		s_yfrac += dy_frac;
+		if (s_yfrac > 0) {
+			s_y2++;
+			s_yfrac -= dest_height;
+		}
+
+		s_x1 = 0;
+		s_xfrac = -dest_width/2;
+		while (s_x1 < source_width) {
+			s_x2 = s_x1 + dx;
+			s_xfrac += dx_frac;
+			if (s_xfrac > 0) {
+				s_x2++;
+				s_xfrac -= dest_width;
+			}
+
+			/* Average block of [x1,x2[ x [y1,y2[ and store in dest */
+			r = g = b = a = 0;
+			n_pixels = 0;
+
+			src = src_pixels + s_y1 * source_rowstride + s_x1 * pixel_stride;
+			for (y = s_y1; y < s_y2; y++) {
+				xsrc = src;
+				if (has_alpha) {
+					for (x = 0; x < s_x2-s_x1; x++) {
+						n_pixels++;
+						
+						r += xsrc[3] * xsrc[0];
+						g += xsrc[3] * xsrc[1];
+						b += xsrc[3] * xsrc[2];
+						a += xsrc[3];
+						xsrc += 4;
+					}
+				} else {
+					for (x = 0; x < s_x2-s_x1; x++) {
+						n_pixels++;
+						r += *xsrc++;
+						g += *xsrc++;
+						b += *xsrc++;
+					}
+				}
+				src += source_rowstride;
+			}
+			
+			if (has_alpha) {
+				if (a != 0) {
+					*dest++ = r / a;
+					*dest++ = g / a;
+					*dest++ = b / a;
+					*dest++ = a / n_pixels;
+				} else {
+					*dest++ = 0;
+					*dest++ = 0;
+					*dest++ = 0;
+					*dest++ = 0;
+				}
+			} else {
+				*dest++ = r / n_pixels;
+				*dest++ = g / n_pixels;
+				*dest++ = b / n_pixels;
+			}
+			
+			s_x1 = s_x2;
+		}
+		s_y1 = s_y2;
+		dest += dest_rowstride - dest_width * pixel_stride;
+	}
+	
+	return dest_pixbuf;
+}
+
+static char *
+get_target_uri (GFile *file)
+{
+	GFileInfo *info;
+	char *target;
+
+	info = g_file_query_info (file, G_FILE_ATTRIBUTE_STANDARD_TARGET_URI, G_FILE_QUERY_INFO_NONE, NULL, NULL);
+	if (info == NULL)
+		return NULL;
+	target = g_strdup (g_file_info_get_attribute_string (info, G_FILE_ATTRIBUTE_STANDARD_TARGET_URI));
+	g_object_unref (info);
+
+	return target;
+}
+
+static char *
+get_target_path (GFile *input)
+{
+	if (g_file_has_uri_scheme (input, "trash") != FALSE ||
+	    g_file_has_uri_scheme (input, "recent") != FALSE) {
+		GFile *file;
+		char *input_uri;
+		char *input_path;
+
+		input_uri = get_target_uri (input);
+		file = g_file_new_for_uri (input_uri);
+		g_free (input_uri);
+		input_path = g_file_get_path (file);
+		g_object_unref (file);
+		return input_path;
+	}
+	return g_file_get_path (input);
+}
+
+static const GOptionEntry entries[] = {
+	{ "size", 's', 0, G_OPTION_ARG_INT, &output_size, "Size of the thumbnail in pixels", NULL },
+	{"g-fatal-warnings", 0, 0, G_OPTION_ARG_NONE, &g_fatal_warnings, "Make all warnings fatal", NULL},
+	{ G_OPTION_REMAINING, '\0', 0, G_OPTION_ARG_FILENAME_ARRAY, &filenames, NULL, "[INPUT FILE] [OUTPUT FILE]" },
+	{ NULL }
+};
+
+int main (int argc, char **argv)
+{
+	char *input_filename;
+	GdkPixbuf *pixbuf;
+	GError *error = NULL;
+	GOptionContext *context;
+	GFile *input;
+	const char *output;
+
+#ifdef THUMBNAILER_RETURNS_PIXBUF
+	int width, height;
+#elif THUMBNAILER_RETURNS_DATA
+	char *data = NULL;
+	gsize length;
+#endif
+
+	g_type_init ();
+
+	/* Options parsing */
+	context = g_option_context_new (THUMBNAILER_USAGE);
+	g_option_context_add_main_entries (context, entries, NULL);
+
+	if (g_option_context_parse (context, &argc, &argv, &error) == FALSE) {
+		g_warning ("Couldn't parse command-line options: %s", error->message);
+		g_error_free (error);
+		return 1;
+	}
+
+	/* Set fatal warnings if required */
+	if (g_fatal_warnings) {
+		GLogLevelFlags fatal_mask;
+
+		fatal_mask = g_log_set_always_fatal (G_LOG_FATAL_MASK);
+		fatal_mask |= G_LOG_LEVEL_WARNING | G_LOG_LEVEL_CRITICAL;
+		g_log_set_always_fatal (fatal_mask);
+	}
+
+	if (filenames == NULL || g_strv_length (filenames) != 2) {
+		g_print ("Expects an input and an output file\n");
+		return 1;
+	}
+
+	input = g_file_new_for_commandline_arg (filenames[0]);
+	input_filename = get_target_path (input);
+	g_object_unref (input);
+
+	if (input_filename == NULL) {
+		g_warning ("Could not get file path for %s", filenames[0]);
+		return 1;
+	}
+
+	output = filenames[1];
+
+#ifdef THUMBNAILER_RETURNS_PIXBUF
+	pixbuf = file_to_pixbuf (input_filename, output_size, &error);
+
+	width = gdk_pixbuf_get_width (pixbuf);
+	height = gdk_pixbuf_get_height (pixbuf);
+
+	/* Handle naive thumbnailers that don't resize */
+	if (output_size != 0 &&
+	    (height > output_size || width > output_size)) {
+		GdkPixbuf *scaled;
+		double scale;
+
+		scale = (double)output_size / MAX (width, height);
+
+		scaled = gnome_desktop_thumbnail_scale_down_pixbuf (pixbuf,
+								    floor (width * scale + 0.5),
+								    floor (height * scale + 0.5));
+		gdk_pixbuf_copy_options (pixbuf, scaled);
+		g_object_unref (pixbuf);
+		pixbuf = scaled;
+	}
+#elif THUMBNAILER_RETURNS_DATA
+	data = file_to_data (input_filename, &length, &error);
+	if (data) {
+		GInputStream *mem_stream;
+
+		mem_stream = g_memory_input_stream_new_from_data (data, length, g_free);
+		pixbuf = gdk_pixbuf_new_from_stream_at_scale (mem_stream, output_size, -1, TRUE, NULL, &error);
+		g_object_unref (mem_stream);
+	} else {
+		pixbuf = NULL;
+	}
+#else
+#error "One of THUMBNAILER_RETURNS_PIXBUF or THUMBNAILER_RETURNS_DATA must be set"
+#endif
+	g_free (input_filename);
+
+	if (!pixbuf) {
+		g_warning ("Could not thumbnail '%s': %s", filenames[0], error->message);
+		g_error_free (error);
+		g_strfreev (filenames);
+		return 1;
+	}
+
+	if (gdk_pixbuf_save (pixbuf, output, "png", &error, NULL) == FALSE) {
+		g_warning ("Couldn't save the thumbnail '%s' for file '%s': %s", output, filenames[0], error->message);
+		g_error_free (error);
+		return 1;
+	}
+
+	g_object_unref (pixbuf);
+
+	return 0;
+}

thumbnailer/gnome-thumbnailer-skeleton.h

+/*
+ * Copyright (C) 2013 Bastien Nocera <hadess@hadess.net>
+ *
+ * Authors: Bastien Nocera <hadess@hadess.net>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by