[mutter/gnome-3-34] clutter/offscreen-effect: Clear offscreen framebuffer when disabling

[Robert Mader <rmader src gnome org>]

commit 47fe7ac25bf7ba85a5f03de8e30e9faa5b243f9c
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Tue Jan 7 11:58:54 2020 -0300

    clutter/offscreen-effect: Clear offscreen framebuffer when disabling
    
    When changing the 'enabled' property and disabling the offscreen effect,
    it doesn't make sense to preserve the offscreen framebuffer. It's not
    drawing, after all.
    
    Furthermore, because ClutterOffscreenEffect only checks if the offscreen
    framebuffer exists to decide whether or not to redraw, keeping the fbo
    alive is a waste of resources.
    
    Clear the offscreen framebuffer when the effect is disabled or enabled.
    
    Fixes https://gitlab.gnome.org/GNOME/mutter/issues/810
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/992
    
    (cherry picked from commit bf594e9fb6d973259163f73881dd91c8910dd54f)

 clutter/clutter/clutter-offscreen-effect.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)
---
diff --git a/clutter/clutter/clutter-offscreen-effect.c b/clutter/clutter/clutter-offscreen-effect.c
index 02d0f4c06..12ab0f833 100644
--- a/clutter/clutter/clutter-offscreen-effect.c
+++ b/clutter/clutter/clutter-offscreen-effect.c
@@ -467,6 +467,19 @@ clutter_offscreen_effect_paint (ClutterEffect           *effect,
     clutter_offscreen_effect_paint_texture (self);
 }
 
+static void
+clutter_offscreen_effect_notify (GObject    *gobject,
+                                 GParamSpec *pspec)
+{
+  ClutterOffscreenEffect *offscreen_effect = CLUTTER_OFFSCREEN_EFFECT (gobject);
+  ClutterOffscreenEffectPrivate *priv = offscreen_effect->priv;
+
+  if (strcmp (pspec->name, "enabled") == 0)
+    g_clear_pointer (&priv->offscreen, cogl_object_unref);
+
+  G_OBJECT_CLASS (clutter_offscreen_effect_parent_class)->notify (gobject, pspec);
+}
+
 static void
 clutter_offscreen_effect_finalize (GObject *gobject)
 {
@@ -497,6 +510,7 @@ clutter_offscreen_effect_class_init (ClutterOffscreenEffectClass *klass)
   effect_class->paint = clutter_offscreen_effect_paint;
 
   gobject_class->finalize = clutter_offscreen_effect_finalize;
+  gobject_class->notify = clutter_offscreen_effect_notify;
 }
 
 static void