[mutter] clutter/stage-view: Use cogl_blit_framebuffer() for shadow FB

[Jonas Ådahl <jadahl src gnome org>]

commit 05e1a6c2ca3cd6222590033e5978a9d9f6d22526
Author: Olivier Fourdan <ofourdan redhat com>
Date:   Thu Sep 26 10:20:36 2019 +0200

    clutter/stage-view: Use cogl_blit_framebuffer() for shadow FB
    
    If there is no transformation, use `cogl_blit_framebuffer()` as a
    shortcut in `clutter_stage_view_blit_offscreen()`, that dramatically
    improves performance when using a shadow framebuffer.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/809

 clutter/clutter/clutter-stage-view.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)
---
diff --git a/clutter/clutter/clutter-stage-view.c b/clutter/clutter/clutter-stage-view.c
index a12261f44..7db079f78 100644
--- a/clutter/clutter/clutter-stage-view.c
+++ b/clutter/clutter/clutter-stage-view.c
@@ -143,6 +143,18 @@ clutter_stage_view_blit_offscreen (ClutterStageView            *view,
     clutter_stage_view_get_instance_private (view);
   CoglMatrix matrix;
 
+  clutter_stage_view_get_offscreen_transformation_matrix (view, &matrix);
+  if (cogl_matrix_is_identity (&matrix))
+    {
+      if (cogl_blit_framebuffer (priv->offscreen,
+                                 priv->framebuffer,
+                                 rect->x, rect->y,
+                                 rect->x, rect->y,
+                                 rect->width, rect->height,
+                                 NULL))
+        return;
+    }
+
   clutter_stage_view_ensure_offscreen_blit_pipeline (view);
   cogl_framebuffer_push_matrix (priv->framebuffer);