[gnome-shell] [transitions] Do not recreate FBOs on opacity changes

[Florian Müllner <fmuellner src gnome org>]

commit 5bd977dd3c9e6183ed6c5fce9af98b29e661685d
Author: Florian Müllner <fmuellner gnome org>
Date:   Tue Aug 17 13:30:12 2010 +0200

    [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

 src/st/st-theme-node-transition.c |   35 +++++++++++++++++------------------
 1 files changed, 17 insertions(+), 18 deletions(-)
---
diff --git a/src/st/st-theme-node-transition.c b/src/st/st-theme-node-transition.c
index 78be966..9dbb45c 100644
--- 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,