[mutter/gnome-3-38] clutter/stage-view: Disable double buffered shadow buffering

[Marge Bot <marge-bot src gnome org>]

commit 95b683ae2e912e07aade5308fca90d8a90d3b8aa
Author: Jonas Ådahl <jadahl gmail com>
Date:   Wed Feb 10 09:39:18 2021 +0100

    clutter/stage-view: Disable double buffered shadow buffering
    
    To make the double buffered shadow buffer damaged tiles detection
    feasable, a new EGL extension is needed for creating FBO's backed by
    a custom CPU memory buffer, instead of DMA buffers, as DMA buffers can
    be very slow to read, much slower than just painting the shadow buffer
    directly.
    
    Leave the code there, since such an EGL extension is intended to be
    added, but hide it behind an env var so that it isn't enabled by
    accident.
    
    (cherry picked from commit ad5b5f2c57dd0dcb9e586ea09486eebff89fb94d)
    
    https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1724
    
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1743>

 clutter/clutter/clutter-stage-view.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)
---
diff --git a/clutter/clutter/clutter-stage-view.c b/clutter/clutter/clutter-stage-view.c
index 00a4d5ad14..ccc07cd6c8 100644
--- a/clutter/clutter/clutter-stage-view.c
+++ b/clutter/clutter/clutter-stage-view.c
@@ -415,15 +415,19 @@ init_shadowfb (ClutterStageView *view)
   height = cogl_framebuffer_get_height (priv->framebuffer);
   cogl_context = cogl_framebuffer_get_context (priv->framebuffer);
 
-  if (init_dma_buf_shadowfbs (view, cogl_context, width, height, &error))
+  if (g_strcmp0 (g_getenv ("MUTTER_DEBUG_ENABLE_DOUBLE_SHADOWFB"), "1") == 0)
     {
-      g_message ("Initialized double buffered shadow fb for %s", priv->name);
-      return;
-    }
+      if (init_dma_buf_shadowfbs (view, cogl_context, width, height, &error))
+        {
+          g_message ("Initialized double buffered shadow fb for %s",
+                     priv->name);
+          return;
+        }
 
-  g_warning ("Failed to initialize double buffered shadow fb for %s: %s",
-             priv->name, error->message);
-  g_clear_error (&error);
+      g_warning ("Failed to initialize double buffered shadow fb for %s: %s",
+                 priv->name, error->message);
+      g_clear_error (&error);
+    }
 
   if (!init_fallback_shadowfb (view, cogl_context, width, height, &error))
     {