[gnome-software] Show the desktop background behind the screenshot in some instances

[Richard Hughes <rhughes src gnome org>]

commit b46eb203f150e5d2003ce2d9cf596e45dec4818d
Author: Richard Hughes <richard hughsie com>
Date:   Fri Jul 4 13:10:02 2014 +0100

    Show the desktop background behind the screenshot in some instances
    
    We only do this if the screenshot has internal alpha areas detected.

 src/Makefile.am           |    1 +
 src/gs-screenshot-image.c |  100 +++++++++++++++++++++++++++++++++++++--------
 2 files changed, 84 insertions(+), 17 deletions(-)
---
diff --git a/src/Makefile.am b/src/Makefile.am
index 1ea0b65..0e00a4e 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -174,6 +174,7 @@ gnome_software_LDADD =                                      \
        $(GTK_LIBS)                                     \
        $(SOUP_LIBS)                                    \
        $(PACKAGEKIT_LIBS)                              \
+       $(GNOME_DESKTOP_LIBS)                           \
        -lm
 
 gnome_software_CFLAGS =                                        \
diff --git a/src/gs-screenshot-image.c b/src/gs-screenshot-image.c
index 09f7820..3ec692a 100644
--- a/src/gs-screenshot-image.c
+++ b/src/gs-screenshot-image.c
@@ -25,6 +25,10 @@
 #include <glib/gi18n.h>
 #include <gtk/gtk.h>
 
+#define GNOME_DESKTOP_USE_UNSTABLE_API
+#include <libgnome-desktop/gnome-bg.h>
+#include <libgnome-desktop/gnome-desktop-thumbnail.h>
+
 #include "gs-screenshot-image.h"
 
 struct _GsScreenshotImagePrivate
@@ -90,40 +94,102 @@ gs_screenshot_image_set_error (GsScreenshotImage *ssimg, const gchar *message)
 }
 
 /**
+ * gs_screenshot_image_get_desktop_pixbuf:
+ **/
+static GdkPixbuf *
+gs_screenshot_image_get_desktop_pixbuf (GsScreenshotImage *ssimg)
+{
+       GdkPixbuf *pixbuf;
+       GnomeBG *bg;
+       GnomeDesktopThumbnailFactory *factory;
+       GSettings *settings;
+       GsScreenshotImagePrivate *priv;
+
+       priv = gs_screenshot_image_get_instance_private (ssimg);
+
+       factory = gnome_desktop_thumbnail_factory_new (GNOME_DESKTOP_THUMBNAIL_SIZE_LARGE);
+       bg = gnome_bg_new ();
+       settings = g_settings_new ("org.gnome.desktop.background");
+       gnome_bg_load_from_preferences (bg, settings);
+       pixbuf = gnome_bg_create_thumbnail (bg, factory, gdk_screen_get_default (), priv->width, 
priv->height);
+       g_object_unref (bg);
+       g_object_unref (factory);
+       g_object_unref (settings);
+       return pixbuf;
+}
+
+/**
+ * gs_screenshot_image_use_desktop_background:
+ **/
+static gboolean
+gs_screenshot_image_use_desktop_background (GdkPixbuf *pixbuf)
+{
+       AsImage *im;
+       gboolean ret;
+
+       /* nothing to show, means no background mode */
+       if (pixbuf == NULL)
+               return FALSE;
+
+       /* use a temp AsImage */
+       im = as_image_new ();
+       as_image_set_pixbuf (im, pixbuf);
+       ret = (as_image_get_alpha_flags (im) & AS_IMAGE_ALPHA_FLAG_INTERNAL) > 0;
+       g_object_unref (im);
+       return ret;
+}
+
+/**
  * as_screenshot_show_image:
  **/
 static void
 as_screenshot_show_image (GsScreenshotImage *ssimg)
 {
-       GdkPixbuf *pixbuf;
+       GdkPixbuf *pixbuf_bg = NULL;
+       GdkPixbuf *pixbuf = NULL;
        GsScreenshotImagePrivate *priv;
 
        priv = gs_screenshot_image_get_instance_private (ssimg);
 
+       /* this is always going to have alpha */
+       pixbuf = gdk_pixbuf_new_from_file_at_scale (priv->filename,
+                                                   priv->width,
+                                                   priv->height,
+                                                   FALSE, NULL);
+       if (pixbuf != NULL) {
+               if (gs_screenshot_image_use_desktop_background (pixbuf)) {
+                       pixbuf_bg = gs_screenshot_image_get_desktop_pixbuf (ssimg);
+                       if (pixbuf_bg == NULL) {
+                               pixbuf_bg = g_object_ref (pixbuf);
+                       } else {
+                               gdk_pixbuf_composite (pixbuf, pixbuf_bg,
+                                                     0, 0,
+                                                     priv->width, priv->height,
+                                                     0, 0, 1.0f, 1.0f,
+                                                     GDK_INTERP_NEAREST, 255);
+                       }
+               } else {
+                       pixbuf_bg = g_object_ref (pixbuf);
+               }
+       }
+
        /* show icon */
        if (g_strcmp0 (priv->current_image, "image1") == 0) {
-               pixbuf = gdk_pixbuf_new_from_file_at_scale (priv->filename,
-                                                           priv->width,
-                                                           priv->height,
-                                                           FALSE, NULL);
-               if (pixbuf != NULL) {
-                       gtk_image_set_from_pixbuf (GTK_IMAGE (priv->image2), pixbuf);
-                       g_object_unref (pixbuf);
-               }
+               if (pixbuf_bg != NULL)
+                       gtk_image_set_from_pixbuf (GTK_IMAGE (priv->image2), pixbuf_bg);
                gtk_stack_set_visible_child_name (GTK_STACK (priv->stack), "image2");
                priv->current_image = "image2";
        } else {
-               pixbuf = gdk_pixbuf_new_from_file_at_scale (priv->filename,
-                                                           priv->width,
-                                                           priv->height,
-                                                           FALSE, NULL);
-               if (pixbuf != NULL) {
-                       gtk_image_set_from_pixbuf (GTK_IMAGE (priv->image1), pixbuf);
-                       g_object_unref (pixbuf);
-               }
+               if (pixbuf_bg != NULL)
+                       gtk_image_set_from_pixbuf (GTK_IMAGE (priv->image1), pixbuf_bg);
                gtk_stack_set_visible_child_name (GTK_STACK (priv->stack), "image1");
                priv->current_image = "image1";
        }
+
+       if (pixbuf != NULL)
+               g_object_unref (pixbuf);
+       if (pixbuf_bg != NULL)
+               g_object_unref (pixbuf_bg);
        gtk_widget_show (GTK_WIDGET (ssimg));
 }