screen: Remove alt-tab thumbnails

gdk_pixbuf_scale_simple generates very nice thumbnails at the expense of
a very slow rendering. So slow that the alt-tab popup is not usable: it
needs 3.6 seconds to downscale 30 windows of dimension 1600x900 on an
fairly recent computer.

We remove the thumbnailing to makes alt-tab blazing fast again in the
composited mode.

https://bugzilla.gnome.org/show_bug.cgi?id=504729

1 files changed, 13 insertions, 74 deletions

diff --git a/src/core/screen.c b/src/core/screen.c
index 34dcdc3b..52e020a6 100644
--- a/src/core/screen.c
+++ b/src/core/screen.c
@@ -1197,49 +1197,6 @@ meta_screen_update_cursor (MetaScreen *screen)
   XFreeCursor (screen->display->xdisplay, xcursor);
 }
 
-#define MAX_PREVIEW_SIZE 150.0
-
-static GdkPixbuf *
-get_window_pixbuf (MetaWindow *window,
-                   int        *width,
-                   int        *height)
-{
-  Pixmap pmap;
-  GdkPixbuf *pixbuf, *scaled;
-  double ratio;
-
-  pmap = meta_compositor_get_window_pixmap (window->display->compositor,
-                                            window);
-  if (pmap == None)
-    return NULL;
-
-  pixbuf = meta_ui_get_pixbuf_from_pixmap (pmap);
-  if (pixbuf == NULL) 
-    return NULL;
-
-  *width = gdk_pixbuf_get_width (pixbuf);
-  *height = gdk_pixbuf_get_height (pixbuf);
-
-  /* Scale pixbuf to max dimension MAX_PREVIEW_SIZE */
-  if (*width > *height)
-    {
-      ratio = ((double) *width) / MAX_PREVIEW_SIZE;
-      *width = (int) MAX_PREVIEW_SIZE;
-      *height = (int) (((double) *height) / ratio);
-    }
-  else
-    {
-      ratio = ((double) *height) / MAX_PREVIEW_SIZE;
-      *height = (int) MAX_PREVIEW_SIZE;
-      *width = (int) (((double) *width) / ratio);
-    }
-
-  scaled = gdk_pixbuf_scale_simple (pixbuf, *width, *height,
-                                    GDK_INTERP_BILINEAR);
-  g_object_unref (pixbuf);
-  return scaled;
-}
-                                         
 void
 meta_screen_ensure_tab_popup (MetaScreen      *screen,
                               MetaTabList      list_type,
@@ -1272,41 +1229,23 @@ meta_screen_ensure_tab_popup (MetaScreen      *screen,
     {
       MetaWindow *window;
       MetaRectangle r;
-      GdkPixbuf *win_pixbuf;
-      int width, height;
 
       window = tmp->data;
-      
+
+      /* Metacity used to generated a thumbnail of the window contents
+       * using gdk_pixbuf_simple_scale which is so slow with bilinear
+       * interpolation that it has been removed.
+       *
+       * The cairo downscale could have been an alternative, but the
+       * result is terrible ATM, so it is simply better to have the
+       * same user story as the non-composited case (no thumbnail).
+       *
+       * https://bugzilla.gnome.org/show_bug.cgi?id=504729
+       */
+
       entries[i].key = (MetaTabEntryKey) window->xwindow;
       entries[i].title = window->title;
-
-      win_pixbuf = get_window_pixbuf (window, &width, &height);
-      if (win_pixbuf == NULL)
-        entries[i].icon = g_object_ref (window->icon);
-      else
-        {
-          int icon_width, icon_height, t_width, t_height;
-#define ICON_OFFSET 6
-
-          icon_width = gdk_pixbuf_get_width (window->icon);
-          icon_height = gdk_pixbuf_get_height (window->icon);
-
-          t_width = width + ICON_OFFSET;
-          t_height = height + ICON_OFFSET;
-
-          entries[i].icon = gdk_pixbuf_new (GDK_COLORSPACE_RGB, TRUE, 8,
-                                            t_width, t_height);
-          gdk_pixbuf_fill (entries[i].icon, 0x00000000);
-          gdk_pixbuf_copy_area (win_pixbuf, 0, 0, width, height,
-                                entries[i].icon, 0, 0);
-          g_object_unref (win_pixbuf);
-          gdk_pixbuf_composite (window->icon, entries[i].icon, 
-                                t_width - icon_width, t_height - icon_height,
-                                icon_width, icon_height,
-                                t_width - icon_width, t_height - icon_height, 
-                                1.0, 1.0, GDK_INTERP_BILINEAR, 255);
-        }
-                                
+      entries[i].icon = g_object_ref (window->icon);
       entries[i].blank = FALSE;
       entries[i].hidden = !meta_window_showing_on_its_workspace (window);
       entries[i].demands_attention = window->wm_state_demands_attention;