compositor/native: Track what Wayland surface is a scanout candidate

For the current candidate, set the candidate CRTC on that surface. This
will later be used to send DMA buffer feedback for direct scanout purposes.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1959>

src/compositor/meta-compositor-native.c

@@ -23,11 +23,14 @@
 #include "compositor/meta-compositor-native.h"
 
 #include "backends/meta-logical-monitor.h"
+#include "backends/native/meta-crtc-kms.h"
 #include "compositor/meta-surface-actor-wayland.h"
 
 struct _MetaCompositorNative
 {
   MetaCompositorServer parent;
+
+  MetaWaylandSurface *current_scanout_candidate;
 };
 
 G_DEFINE_TYPE (MetaCompositorNative, meta_compositor_native,
@@ -62,57 +65,88 @@ get_window_view (MetaRenderer *renderer,
 static void
 maybe_assign_primary_plane (MetaCompositor *compositor)
 {
+  MetaCompositorNative *compositor_native = META_COMPOSITOR_NATIVE (compositor);
   MetaBackend *backend = meta_get_backend ();
   MetaRenderer *renderer = meta_backend_get_renderer (backend);
   MetaWindowActor *window_actor;
   MetaWindow *window;
   MetaRendererView *view;
+  MetaCrtc *crtc;
   CoglFramebuffer *framebuffer;
   CoglOnscreen *onscreen;
   MetaSurfaceActor *surface_actor;
   MetaSurfaceActorWayland *surface_actor_wayland;
+  MetaWaylandSurface *surface;
+  MetaWaylandSurface *old_candidate =
+    compositor_native->current_scanout_candidate;
+  MetaWaylandSurface *new_candidate = NULL;
   g_autoptr (CoglScanout) scanout = NULL;
 
   if (meta_compositor_is_unredirect_inhibited (compositor))
-    return;
+    goto done;
 
   window_actor = meta_compositor_get_top_window_actor (compositor);
   if (!window_actor)
-    return;
+    goto done;
 
   if (meta_window_actor_effect_in_progress (window_actor))
-    return;
+    goto done;
 
   if (clutter_actor_has_transitions (CLUTTER_ACTOR (window_actor)))
-    return;
+    goto done;
 
   if (clutter_actor_get_n_children (CLUTTER_ACTOR (window_actor)) != 1)
-    return;
+    goto done;
 
   window = meta_window_actor_get_meta_window (window_actor);
   if (!window)
-    return;
+    goto done;
 
   view = get_window_view (renderer, window);
   if (!view)
-    return;
+    goto done;
+
+  crtc = meta_renderer_view_get_crtc (META_RENDERER_VIEW (view));
+  if (!META_IS_CRTC_KMS (crtc))
+    goto done;
 
   framebuffer = clutter_stage_view_get_framebuffer (CLUTTER_STAGE_VIEW (view));
   if (!COGL_IS_ONSCREEN (framebuffer))
-    return;
+    goto done;
 
   surface_actor = meta_window_actor_get_surface (window_actor);
   if (!META_IS_SURFACE_ACTOR_WAYLAND (surface_actor))
-    return;
-
+    goto done;
   surface_actor_wayland = META_SURFACE_ACTOR_WAYLAND (surface_actor);
+
+  surface = meta_surface_actor_wayland_get_surface (surface_actor_wayland);
+  if (!surface)
+    goto done;
+
+  new_candidate = surface;
+
   onscreen = COGL_ONSCREEN (framebuffer);
   scanout = meta_surface_actor_wayland_try_acquire_scanout (surface_actor_wayland,
                                                             onscreen);
   if (!scanout)
-    return;
+    goto done;
 
   clutter_stage_view_assign_next_scanout (CLUTTER_STAGE_VIEW (view), scanout);
+
+done:
+
+  if (old_candidate && old_candidate != new_candidate)
+    {
+      meta_wayland_surface_set_scanout_candidate (old_candidate, NULL);
+      g_clear_weak_pointer (&compositor_native->current_scanout_candidate);
+    }
+
+  if (new_candidate)
+    {
+      meta_wayland_surface_set_scanout_candidate (surface, crtc);
+      g_set_weak_pointer (&compositor_native->current_scanout_candidate,
+                          surface);
+    }
 }
 
 static void
@@ -137,6 +171,16 @@ meta_compositor_native_new (MetaDisplay *display,
                        NULL);
 }
 
+static void
+meta_compositor_native_finalize (GObject *object)
+{
+  MetaCompositorNative *compositor_native = META_COMPOSITOR_NATIVE (object);
+
+  g_clear_weak_pointer (&compositor_native->current_scanout_candidate);
+
+  G_OBJECT_CLASS (meta_compositor_native_parent_class)->finalize (object);
+}
+
 static void
 meta_compositor_native_init (MetaCompositorNative *compositor_native)
 {
@@ -145,7 +189,10 @@ meta_compositor_native_init (MetaCompositorNative *compositor_native)
 static void
 meta_compositor_native_class_init (MetaCompositorNativeClass *klass)
 {
+  GObjectClass *object_class = G_OBJECT_CLASS (klass);
   MetaCompositorClass *compositor_class = META_COMPOSITOR_CLASS (klass);
 
+  object_class->finalize = meta_compositor_native_finalize;
+
   compositor_class->before_paint = meta_compositor_native_before_paint;
 }

src/compositor/meta-surface-actor-wayland.c

@@ -79,8 +79,7 @@ meta_surface_actor_wayland_try_acquire_scanout (MetaSurfaceActorWayland *self,
     return NULL;
 
   surface = meta_surface_actor_wayland_get_surface (self);
-  if (!surface)
-    return NULL;
+  g_return_val_if_fail (surface, NULL);
 
   scanout = meta_wayland_surface_try_acquire_scanout (surface, onscreen);
   if (!scanout)

src/wayland/meta-wayland-surface.c

@@ -77,6 +77,17 @@ typedef struct _MetaWaylandSurfaceRolePrivate
   MetaWaylandSurface *surface;
 } MetaWaylandSurfaceRolePrivate;
 
+enum
+{
+  PROP_0,
+
+  PROP_SCANOUT_CANDIDATE,
+
+  N_PROPS
+};
+
+static GParamSpec *obj_props[N_PROPS];
+
 G_DEFINE_TYPE (MetaWaylandSurface, meta_wayland_surface, G_TYPE_OBJECT);
 
 G_DEFINE_ABSTRACT_TYPE_WITH_PRIVATE (MetaWaylandSurfaceRole,
@@ -1412,6 +1423,7 @@ wl_surface_destructor (struct wl_resource *resource)
 
   g_signal_emit (surface, surface_signals[SURFACE_DESTROY], 0);
 
+  g_clear_object (&surface->scanout_candidate);
   g_clear_object (&surface->role);
 
   if (surface->unassigned.buffer)
@@ -1693,11 +1705,41 @@ meta_wayland_surface_init (MetaWaylandSurface *surface)
     g_node_prepend_data (surface->subsurface_branch_node, surface);
 }
 
+static void
+meta_wayland_surface_get_property (GObject    *object,
+                                   guint       prop_id,
+                                   GValue     *value,
+                                   GParamSpec *pspec)
+{
+  MetaWaylandSurface *surface = META_WAYLAND_SURFACE (object);
+
+  switch (prop_id)
+    {
+    case PROP_SCANOUT_CANDIDATE:
+      g_value_set_object (value, surface->scanout_candidate);
+      break;
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+      break;
+    }
+}
+
 static void
 meta_wayland_surface_class_init (MetaWaylandSurfaceClass *klass)
 {
   GObjectClass *object_class = G_OBJECT_CLASS (klass);
 
+  object_class->get_property = meta_wayland_surface_get_property;
+
+  obj_props[PROP_SCANOUT_CANDIDATE] =
+    g_param_spec_object ("scanout-candidate",
+                         "scanout-candidate",
+                         "Scanout candidate for given CRTC",
+                         META_TYPE_CRTC,
+                         G_PARAM_READABLE |
+                         G_PARAM_STATIC_STRINGS);
+  g_object_class_install_properties (object_class, N_PROPS, obj_props);
+
   surface_signals[SURFACE_DESTROY] =
     g_signal_new ("destroy",
                   G_TYPE_FROM_CLASS (object_class),
@@ -2100,3 +2142,21 @@ meta_wayland_surface_try_acquire_scanout (MetaWaylandSurface *surface,
 
   return scanout;
 }
+
+MetaCrtc *
+meta_wayland_surface_get_scanout_candidate (MetaWaylandSurface *surface)
+{
+  return surface->scanout_candidate;
+}
+
+void
+meta_wayland_surface_set_scanout_candidate (MetaWaylandSurface *surface,
+                                            MetaCrtc           *crtc)
+{
+  if (surface->scanout_candidate == crtc)
+    return;
+
+  g_set_object (&surface->scanout_candidate, crtc);
+  g_object_notify_by_pspec (G_OBJECT (surface),
+                            obj_props[PROP_SCANOUT_CANDIDATE]);
+}

src/wayland/meta-wayland-surface.h

@@ -247,6 +247,9 @@ struct _MetaWaylandSurface
      */
     uint64_t sequence;
   } presentation_time;
+
+  /* dma-buf feedback */
+  MetaCrtc *scanout_candidate;
 };
 
 void                meta_wayland_shell_init     (MetaWaylandCompositor *compositor);
@@ -363,6 +366,11 @@ int                 meta_wayland_surface_get_height (MetaWaylandSurface *surface
 CoglScanout *       meta_wayland_surface_try_acquire_scanout (MetaWaylandSurface *surface,
                                                               CoglOnscreen       *onscreen);
 
+MetaCrtc * meta_wayland_surface_get_scanout_candidate (MetaWaylandSurface *surface);
+
+void meta_wayland_surface_set_scanout_candidate (MetaWaylandSurface *surface,
+                                                 MetaCrtc           *crtc);
+
 static inline GNode *
 meta_get_next_subsurface_sibling (GNode *n)
 {