wayland: change accessible boolean to use_count counter

Since a buffer can be used by multiple surfaces at once,
we need to release the buffer only after all surfaces
are finished with it.  Currently we track whether or
not to release the buffer based on the accessible boolean.
This commit changes it to a counter to accomodate multiple
users.

Also, each surface needs to know whether not it is done with
the buffer, so this commit adds a buffer_used boolean to the
surface state.

https://bugzilla.gnome.org/show_bug.cgi?id=761613

src/wayland/meta-wayland-buffer.c

@@ -51,32 +51,30 @@ void
 meta_wayland_buffer_unref (MetaWaylandBuffer *buffer)
 {
   buffer->ref_count--;
+
   if (buffer->ref_count == 0)
     {
-      g_clear_pointer (&buffer->texture, cogl_object_unref);
+      g_warn_if_fail (buffer->use_count == 0);
 
-      if (buffer->accessible)
-        meta_wayland_buffer_release_control (buffer);
+      g_clear_pointer (&buffer->texture, cogl_object_unref);
     }
 }
 
 void
-meta_wayland_buffer_take_control (MetaWaylandBuffer *buffer)
+meta_wayland_buffer_ref_use_count (MetaWaylandBuffer *buffer)
 {
-  if (buffer->accessible)
-    meta_fatal ("buffer control taken twice");
-
-  buffer->accessible = TRUE;
+  buffer->use_count++;
 }
 
 void
-meta_wayland_buffer_release_control (MetaWaylandBuffer *buffer)
+meta_wayland_buffer_unref_use_count (MetaWaylandBuffer *buffer)
 {
-  if (!buffer->accessible)
-    meta_fatal ("buffer released when not in control");
+  g_return_if_fail (buffer->use_count != 0);
 
+  buffer->use_count--;
+
+  if (buffer->use_count == 0)
     wl_resource_queue_event (buffer->resource, WL_BUFFER_RELEASE);
-  buffer->accessible = FALSE;
 }
 
 MetaWaylandBuffer *
@@ -114,8 +112,7 @@ meta_wayland_buffer_ensure_texture (MetaWaylandBuffer *buffer)
   CoglTexture *texture;
   struct wl_shm_buffer *shm_buffer;
 
-  if (!buffer->accessible)
-    meta_warning ("attempted to process damage on uncommitted buffer");
+  g_return_val_if_fail (buffer->use_count != 0, NULL);
 
   if (buffer->texture)
     goto out;
@@ -150,8 +147,7 @@ meta_wayland_buffer_process_damage (MetaWaylandBuffer *buffer,
 {
   struct wl_shm_buffer *shm_buffer;
 
-  if (!buffer->accessible)
-    meta_warning ("attempted to process damage on uncommitted buffer");
+  g_return_if_fail (buffer->use_count != 0);
 
   shm_buffer = wl_shm_buffer_get (buffer->resource);
 

src/wayland/meta-wayland-buffer.h

@@ -39,15 +39,14 @@ struct _MetaWaylandBuffer
 
   CoglTexture *texture;
   uint32_t ref_count;
-
-  uint32_t accessible : 1;
+  uint32_t use_count;
 };
 
 MetaWaylandBuffer *     meta_wayland_buffer_from_resource       (struct wl_resource    *resource);
 void                    meta_wayland_buffer_ref                 (MetaWaylandBuffer     *buffer);
 void                    meta_wayland_buffer_unref               (MetaWaylandBuffer     *buffer);
-void                    meta_wayland_buffer_take_control        (MetaWaylandBuffer     *buffer);
-void                    meta_wayland_buffer_release_control     (MetaWaylandBuffer     *buffer);
+void                    meta_wayland_buffer_ref_use_count       (MetaWaylandBuffer     *buffer);
+void                    meta_wayland_buffer_unref_use_count     (MetaWaylandBuffer     *buffer);
 CoglTexture *           meta_wayland_buffer_ensure_texture      (MetaWaylandBuffer     *buffer);
 void                    meta_wayland_buffer_process_damage      (MetaWaylandBuffer     *buffer,
                                                                  cairo_region_t        *region);

src/wayland/meta-wayland-surface.c

@@ -174,6 +174,25 @@ meta_wayland_surface_assign_role (MetaWaylandSurface *surface,
     }
 }
 
+static void
+surface_use_buffer (MetaWaylandSurface *surface)
+{
+  g_return_if_fail (!surface->using_buffer);
+
+  meta_wayland_buffer_ref_use_count (surface->buffer);
+  surface->using_buffer = TRUE;
+}
+
+static void
+surface_stop_using_buffer (MetaWaylandSurface *surface)
+{
+  if (!surface->using_buffer)
+    return;
+
+  meta_wayland_buffer_unref_use_count (surface->buffer);
+  surface->using_buffer = FALSE;
+}
+
 static void
 surface_set_buffer (MetaWaylandSurface *surface,
                     MetaWaylandBuffer  *buffer)
@@ -184,6 +203,8 @@ surface_set_buffer (MetaWaylandSurface *surface,
   if (surface->buffer)
     {
       wl_list_remove (&surface->buffer_destroy_listener.link);
+
+      surface_stop_using_buffer (surface);
       meta_wayland_buffer_unref (surface->buffer);
     }
 
@@ -657,11 +678,11 @@ apply_pending_state (MetaWaylandSurface      *surface,
 
       surface_set_buffer (surface, pending->buffer);
 
-      if (pending->buffer)
+      if (pending->buffer && !surface->using_buffer)
         {
           struct wl_shm_buffer *shm_buffer = wl_shm_buffer_get (pending->buffer->resource);
 
-          meta_wayland_buffer_take_control (pending->buffer);
+          surface_use_buffer (surface);
           CoglTexture *texture = meta_wayland_buffer_ensure_texture (pending->buffer);
           meta_surface_actor_wayland_set_texture (META_SURFACE_ACTOR_WAYLAND (surface->surface_actor), texture);
 
@@ -679,7 +700,7 @@ apply_pending_state (MetaWaylandSurface      *surface,
     surface_process_damage (surface, pending->damage);
 
   if (release_new_buffer)
-    meta_wayland_buffer_release_control (pending->buffer);
+    surface_stop_using_buffer (surface);
 
   surface->offset_x += pending->dx;
   surface->offset_y += pending->dy;

src/wayland/meta-wayland-surface.h

@@ -152,6 +152,7 @@ struct _MetaWaylandSurface
   MetaWaylandSurfaceRole *role;
   MetaWindow *window;
   MetaWaylandBuffer *buffer;
+  gboolean using_buffer;
   struct wl_listener buffer_destroy_listener;
   cairo_region_t *input_region;
   cairo_region_t *opaque_region;