clutter-actor: Add a debug flag for disabling offscreen redirect

This adds CLUTTER_PAINT=disable-offscreen-redirect to help diagnose
problems with the correct opacity changes. This just makes it so that
it never installs the flatten effect so it will never automatically
redirect an actor offscreen.

clutter/clutter-actor.c

@@ -2700,6 +2700,10 @@ needs_flatten_effect (ClutterActor *self)
 {
   ClutterActorPrivate *priv = self->priv;
 
+  if (G_UNLIKELY (clutter_paint_debug_flags &
+                  CLUTTER_DEBUG_DISABLE_OFFSCREEN_REDIRECT))
+    return FALSE;
+
   switch (priv->offscreen_redirect)
     {
     case CLUTTER_OFFSCREEN_REDIRECT_AUTOMATIC_FOR_OPACITY:

clutter/clutter-debug.h

@@ -39,7 +39,8 @@ typedef enum {
   CLUTTER_DEBUG_DISABLE_CLIPPED_REDRAWS = 1 << 1,
   CLUTTER_DEBUG_REDRAWS                 = 1 << 2,
   CLUTTER_DEBUG_PAINT_VOLUMES           = 1 << 3,
-  CLUTTER_DEBUG_DISABLE_CULLING         = 1 << 4
+  CLUTTER_DEBUG_DISABLE_CULLING         = 1 << 4,
+  CLUTTER_DEBUG_DISABLE_OFFSCREEN_REDIRECT = 1 << 5
 } ClutterDrawDebugFlag;
 
 #ifdef CLUTTER_ENABLE_DEBUG

clutter/clutter-main.c

@@ -180,7 +180,8 @@ static const GDebugKey clutter_paint_debug_keys[] = {
   { "disable-clipped-redraws", CLUTTER_DEBUG_DISABLE_CLIPPED_REDRAWS },
   { "redraws", CLUTTER_DEBUG_REDRAWS },
   { "paint-volumes", CLUTTER_DEBUG_PAINT_VOLUMES },
-  { "disable-culling", CLUTTER_DEBUG_DISABLE_CULLING }
+  { "disable-culling", CLUTTER_DEBUG_DISABLE_CULLING },
+  { "disable-offscreen-redirect", CLUTTER_DEBUG_DISABLE_OFFSCREEN_REDIRECT }
 };
 
 #ifdef CLUTTER_ENABLE_PROFILE