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

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

commit 393a85971c477419e0c16cf66c349d83651aa223
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.
    
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1724>

 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 a9d77e44a0..9b325e911c 100644
--- a/clutter/clutter/clutter-stage-view.c
+++ b/clutter/clutter/clutter-stage-view.c
@@ -425,15 +425,19 @@ 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))
     {