clutter/view: Make it possible to assign a temporary direct scanout

Make it possible to cause the next frame to scan out directly from the
passed CoglScannout. This makes it possible to completely bypass
compositing for the following frame.

Original Mutter commit: https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/798/diffs?commit_id=753066598ff83fa9bdbd1be23d1e22663ae59297

Author: Sunderland93

clutter/clutter/clutter-muffin.h

@@ -75,6 +75,10 @@ void clutter_stage_thaw_updates (ClutterStage *stage);
 CLUTTER_EXPORT
 void clutter_stage_update_resource_scales (ClutterStage *stage);
 
+CLUTTER_EXPORT
+void clutter_stage_view_assign_next_scanout (ClutterStageView *stage_view,
+                                             CoglScanout      *scanout);
+
 CLUTTER_EXPORT
 gboolean clutter_actor_has_damage (ClutterActor *actor);
 

clutter/clutter/clutter-stage-view-private.h

@@ -43,4 +43,6 @@ const cairo_region_t * clutter_stage_view_peek_redraw_clip (ClutterStageView *vi
 
 cairo_region_t * clutter_stage_view_take_redraw_clip (ClutterStageView *view);
 
+CoglScanout * clutter_stage_view_take_scanout (ClutterStageView *view);
+
 #endif /* __CLUTTER_STAGE_VIEW_PRIVATE_H__ */

clutter/clutter/clutter-stage-view.c

@@ -24,6 +24,8 @@
 #include <math.h>
 
 #include "clutter/clutter-private.h"
+#include "clutter/clutter-muffin.h"
+#include "cogl/cogl.h"
 
 enum
 {
@@ -52,6 +54,8 @@ typedef struct _ClutterStageViewPrivate
   CoglOffscreen *shadowfb;
   CoglPipeline *shadowfb_pipeline;
 
+  CoglScanout *next_scanout;
+
   gboolean has_redraw_clip;
   cairo_region_t *redraw_clip;
 
@@ -407,6 +411,26 @@ clutter_stage_default_get_offscreen_transformation_matrix (ClutterStageView *vie
   cogl_matrix_init_identity (matrix);
 }
 
+void
+clutter_stage_view_assign_next_scanout (ClutterStageView *view,
+                                        CoglScanout      *scanout)
+{
+  ClutterStageViewPrivate *priv =
+    clutter_stage_view_get_instance_private (view);
+
+  g_clear_object (&priv->next_scanout);
+  priv->next_scanout = scanout;
+}
+
+CoglScanout *
+clutter_stage_view_take_scanout (ClutterStageView *view)
+{
+  ClutterStageViewPrivate *priv =
+    clutter_stage_view_get_instance_private (view);
+
+  return g_steal_pointer (&priv->next_scanout);
+}
+
 static void
 clutter_stage_view_get_property (GObject    *object,
                                  guint       prop_id,

clutter/clutter/cogl/clutter-stage-cogl.c

@@ -989,6 +989,20 @@ clutter_stage_cogl_redraw_view (ClutterStageWindow *stage_window,
     }
 }
 
+static void
+clutter_stage_cogl_scanout_view (ClutterStageCogl *stage_cogl,
+                                 ClutterStageView *view,
+                                 CoglScanout      *scanout)
+{
+  CoglFramebuffer *framebuffer = clutter_stage_view_get_framebuffer (view);
+  CoglOnscreen *onscreen;
+
+  g_return_if_fail (cogl_is_onscreen (framebuffer));
+
+  onscreen = COGL_ONSCREEN (framebuffer);
+  cogl_onscreen_direct_scanout (onscreen, scanout);
+}
+
 static void
 clutter_stage_cogl_redraw (ClutterStageWindow *stage_window)
 {
@@ -1016,11 +1030,23 @@ clutter_stage_cogl_redraw (ClutterStageWindow *stage_window)
   for (l = _clutter_stage_window_get_views (stage_window); l; l = l->next)
     {
       ClutterStageView *view = l->data;
+      g_autoptr (CoglScanout) scanout = NULL;
 
       if (!clutter_stage_view_has_redraw_clip (view))
         continue;
 
-      swap_event |= clutter_stage_cogl_redraw_view (stage_window, view);
+      scanout = clutter_stage_view_take_scanout (view);
+      if (scanout)
+        {
+          clutter_stage_cogl_scanout_view (stage_cogl,
+                                           view,
+                                           scanout);
+          swap_event = TRUE;
+        }
+      else
+        {
+          swap_event |= clutter_stage_cogl_redraw_view (stage_window, view);
+        }
     }
 
   if (has_redraw_clip)

cogl/cogl/cogl-onscreen.h

@@ -289,7 +289,7 @@ cogl_onscreen_swap_buffers_with_damage (CoglOnscreen *onscreen,
 /**
  * cogl_onscreen_direct_scanout: (skip)
  */
-void
+COGL_EXPORT void
 cogl_onscreen_direct_scanout (CoglOnscreen *onscreen,
                               CoglScanout  *scanout);