[transitions] Do not recreate FBOs on opacity changes

Creating an FBO may be expensive, so we should avoid the operation
if possible. When transitioning between theme nodes, the widget's
opacity is used to paint to the offscreen textures which are blended
together - this means that the textures have to be recreated each time
the widget's opacity changes. It is much more effective to paint the
textures at full opacity and respect the widget's paint opacity when
blending the textures together.

https://bugzilla.gnome.org/show_bug.cgi?id=627085

diff --git a/src/st/st-theme-node-transition.c b/src/st/st-theme-node-transition.c
index 78be9667c7e3de690835d122bbf03d7535210d51..9dbb45c04a404b542acf2e3cd17c37eaa5217d72 100644 (file)
--- a/src/st/st-theme-node-transition.c
+++ b/src/st/st-theme-node-transition.c
@@ -49,7 +49,6 @@ struct _StThemeNodeTransitionPrivate {
 
   ClutterActorBox last_allocation;
   ClutterActorBox offscreen_box;
-  guint8          last_opacity;
 
   gboolean needs_setup;
 };
@@ -200,8 +199,7 @@ calculate_offscreen_box (StThemeNodeTransition *transition,
 
 static gboolean
 setup_framebuffers (StThemeNodeTransition *transition,
-                    const ClutterActorBox *allocation,
-                    guint8                 paint_opacity)
+                    const ClutterActorBox *allocation)
 {
   StThemeNodeTransitionPrivate *priv = transition->priv;
   CoglColor clear_color = { 0, 0, 0, 0 };
@@ -243,11 +241,17 @@ setup_framebuffers (StThemeNodeTransition *transition,
     cogl_handle_unref (priv->material);
   priv->material = cogl_material_new ();
 
+  cogl_material_set_layer_combine (priv->material, 0,
+                                   "RGBA = REPLACE (TEXTURE)",
+                                   NULL);
   cogl_material_set_layer_combine (priv->material, 1,
                                    "RGBA = INTERPOLATE (PREVIOUS, "
                                                        "TEXTURE, "
                                                        "CONSTANT[A])",
                                    NULL);
+  cogl_material_set_layer_combine (priv->material, 2,
+                                   "RGBA = MODULATE (PREVIOUS, PRIMARY)",
+                                   NULL);
 
   cogl_material_set_layer (priv->material, 0, priv->new_texture);
   cogl_material_set_layer (priv->material, 1, priv->old_texture);
@@ -257,9 +261,7 @@ setup_framebuffers (StThemeNodeTransition *transition,
   cogl_ortho (priv->offscreen_box.x1, priv->offscreen_box.x2,
               priv->offscreen_box.y2, priv->offscreen_box.y1,
               0.0, 1.0);
-  st_theme_node_paint (priv->old_theme_node,
-                       allocation,
-                       paint_opacity);
+  st_theme_node_paint (priv->old_theme_node, allocation, 255);
   cogl_pop_framebuffer ();
 
   cogl_push_framebuffer (priv->new_offscreen);
@@ -267,9 +269,7 @@ setup_framebuffers (StThemeNodeTransition *transition,
   cogl_ortho (priv->offscreen_box.x1, priv->offscreen_box.x2,
               priv->offscreen_box.y2, priv->offscreen_box.y1,
               0.0, 1.0);
-  st_theme_node_paint (priv->new_theme_node,
-                       allocation,
-                       paint_opacity);
+  st_theme_node_paint (priv->new_theme_node, allocation, 255);
   cogl_pop_framebuffer ();
 
   return TRUE;
@@ -291,26 +291,25 @@ st_theme_node_transition_paint (StThemeNodeTransition *transition,
   g_return_if_fail (ST_IS_THEME_NODE (priv->old_theme_node));
   g_return_if_fail (ST_IS_THEME_NODE (priv->new_theme_node));
 
-  if (!clutter_actor_box_equal (allocation, &priv->last_allocation) ||
-      paint_opacity != priv->last_opacity)
+  if (!clutter_actor_box_equal (allocation, &priv->last_allocation))
     priv->needs_setup = TRUE;
 
   if (priv->needs_setup)
     {
       priv->last_allocation = *allocation;
-      priv->last_opacity = paint_opacity;
 
       calculate_offscreen_box (transition, allocation);
-      priv->needs_setup = !setup_framebuffers (transition,
-                                               allocation,
-                                               paint_opacity);
+      priv->needs_setup = !setup_framebuffers (transition, allocation);
     }
 
-  cogl_color_set_from_4ub (&constant, 0, 0, 0,
-                           clutter_alpha_get_alpha (priv->alpha) * paint_opacity);
-
+  cogl_color_set_from_4f (&constant, 0., 0., 0.,
+                          clutter_alpha_get_alpha (priv->alpha));
   cogl_material_set_layer_combine_constant (priv->material, 1, &constant);
 
+  cogl_material_set_color4ub (priv->material,
+                              paint_opacity, paint_opacity,
+                              paint_opacity, paint_opacity);
+
   cogl_set_source (priv->material);
   cogl_rectangle_with_multitexture_coords (priv->offscreen_box.x1,
                                            priv->offscreen_box.y1,