backends: Allow multiple "SW" cursor overlays on the stage

All the upper layers are prepared for multiple onscreen cursors, but
this. All MetaCursorRenderers created would poke the same internal
MetaOverlay in the stage.

This will lead to multiple cursor renderers resorting to the "SW"
rendering paths (as it can be seen with tablet support) to reuse the
same overlay, thus leading to flickering when a different
MetaCursorRenderer takes over the overlay.

Fix this by allowing per-cursor-renderer overlays, their lifetime
is attached to the cursor renderer, so is expected to be tear down
if the relevant device (eg. tablet) disappears.

src/backends/meta-cursor-renderer.c

@@ -40,6 +40,7 @@ struct _MetaCursorRendererPrivate
   int current_x, current_y;
 
   MetaCursorSprite *displayed_cursor;
+  MetaOverlay *stage_overlay;
   gboolean handled_by_backend;
 };
 typedef struct _MetaCursorRendererPrivate MetaCursorRendererPrivate;
@@ -63,12 +64,16 @@ queue_redraw (MetaCursorRenderer *renderer,
   if (!stage)
     return;
 
+  if (!priv->stage_overlay)
+    priv->stage_overlay = meta_stage_create_cursor_overlay (META_STAGE (stage));
+
   if (cursor_sprite && !priv->handled_by_backend)
     texture = meta_cursor_sprite_get_cogl_texture (cursor_sprite);
   else
     texture = NULL;
 
-  meta_stage_set_cursor (META_STAGE (stage), texture, &rect);
+  meta_stage_update_cursor_overlay (META_STAGE (stage), priv->stage_overlay,
+                                    texture, &rect);
 }
 
 static gboolean
@@ -81,9 +86,26 @@ meta_cursor_renderer_real_update_cursor (MetaCursorRenderer *renderer,
   return FALSE;
 }
 
+static void
+meta_cursor_renderer_finalize (GObject *object)
+{
+  MetaCursorRenderer *renderer = META_CURSOR_RENDERER (object);
+  MetaCursorRendererPrivate *priv = meta_cursor_renderer_get_instance_private (renderer);
+  MetaBackend *backend = meta_get_backend ();
+  ClutterActor *stage = meta_backend_get_stage (backend);
+
+  if (priv->stage_overlay)
+    meta_stage_remove_cursor_overlay (META_STAGE (stage), priv->stage_overlay);
+
+  G_OBJECT_CLASS (meta_cursor_renderer_parent_class)->finalize (object);
+}
+
 static void
 meta_cursor_renderer_class_init (MetaCursorRendererClass *klass)
 {
+  GObjectClass *object_class = G_OBJECT_CLASS (klass);
+
+  object_class->finalize = meta_cursor_renderer_finalize;
   klass->update_cursor = meta_cursor_renderer_real_update_cursor;
 }
 

src/backends/meta-stage.c

@@ -27,7 +27,7 @@
 #include <meta/meta-backend.h>
 #include <meta/util.h>
 
-typedef struct {
+struct _MetaOverlay {
   gboolean enabled;
 
   CoglPipeline *pipeline;
@@ -36,22 +36,26 @@ typedef struct {
   MetaRectangle current_rect;
   MetaRectangle previous_rect;
   gboolean previous_is_valid;
-} MetaOverlay;
+};
 
 struct _MetaStagePrivate {
-  MetaOverlay cursor_overlay;
+  GList *overlays;
   gboolean is_active;
 };
 typedef struct _MetaStagePrivate MetaStagePrivate;
 
 G_DEFINE_TYPE_WITH_PRIVATE (MetaStage, meta_stage, CLUTTER_TYPE_STAGE);
 
-static void
-meta_overlay_init (MetaOverlay *overlay)
+static MetaOverlay *
+meta_overlay_new ()
 {
+  MetaOverlay *overlay;
   CoglContext *ctx = clutter_backend_get_cogl_context (clutter_get_default_backend ());
 
+  overlay = g_slice_new0 (MetaOverlay);
   overlay->pipeline = cogl_pipeline_new (ctx);
+
+  return overlay;
 }
 
 static void
@@ -59,6 +63,8 @@ meta_overlay_free (MetaOverlay *overlay)
 {
   if (overlay->pipeline)
     cogl_object_unref (overlay->pipeline);
+
+  g_slice_free (MetaOverlay, overlay);
 }
 
 static void
@@ -111,8 +117,15 @@ meta_stage_finalize (GObject *object)
 {
   MetaStage *stage = META_STAGE (object);
   MetaStagePrivate *priv = meta_stage_get_instance_private (stage);
+  GList *l = priv->overlays;
 
-  meta_overlay_free (&priv->cursor_overlay);
+  while (l)
+    {
+      meta_overlay_free (l->data);
+      l = g_list_delete_link (l, l);
+    }
+
+  G_OBJECT_CLASS (meta_stage_parent_class)->finalize (object);
 }
 
 static void
@@ -120,10 +133,12 @@ meta_stage_paint (ClutterActor *actor)
 {
   MetaStage *stage = META_STAGE (actor);
   MetaStagePrivate *priv = meta_stage_get_instance_private (stage);
+  GList *l;
 
   CLUTTER_ACTOR_CLASS (meta_stage_parent_class)->paint (actor);
 
-  meta_overlay_paint (&priv->cursor_overlay);
+  for (l = priv->overlays; l; l = l->next)
+    meta_overlay_paint (l->data);
 }
 
 static void
@@ -166,10 +181,6 @@ meta_stage_class_init (MetaStageClass *klass)
 static void
 meta_stage_init (MetaStage *stage)
 {
-  MetaStagePrivate *priv = meta_stage_get_instance_private (stage);
-
-  meta_overlay_init (&priv->cursor_overlay);
-
   clutter_stage_set_user_resizable (CLUTTER_STAGE (stage), FALSE);
 }
 
@@ -209,17 +220,43 @@ queue_redraw_for_overlay (MetaStage   *stage,
     }
 }
 
+MetaOverlay *
+meta_stage_create_cursor_overlay (MetaStage *stage)
+{
+  MetaStagePrivate *priv = meta_stage_get_instance_private (stage);
+  MetaOverlay *overlay;
+
+  overlay = meta_overlay_new ();
+  priv->overlays = g_list_prepend (priv->overlays, overlay);
+
+  return overlay;
+}
+
 void
-meta_stage_set_cursor (MetaStage     *stage,
+meta_stage_remove_cursor_overlay (MetaStage   *stage,
+                                  MetaOverlay *overlay)
+{
+  MetaStagePrivate *priv = meta_stage_get_instance_private (stage);
+  GList *link;
+
+  link = g_list_find (priv->overlays, overlay);
+  if (!link)
+    return;
+
+  priv->overlays = g_list_delete_link (priv->overlays, link);
+  meta_overlay_free (overlay);
+}
+
+void
+meta_stage_update_cursor_overlay (MetaStage          *stage,
+                                  MetaOverlay        *overlay,
                                   CoglTexture        *texture,
                                   MetaRectangle      *rect)
 {
-  MetaStagePrivate *priv = meta_stage_get_instance_private (stage);
-
   g_assert (meta_is_wayland_compositor () || texture == NULL);
 
-  meta_overlay_set (&priv->cursor_overlay, texture, rect);
-  queue_redraw_for_overlay (stage, &priv->cursor_overlay);
+  meta_overlay_set (overlay, texture, rect);
+  queue_redraw_for_overlay (stage, overlay);
 }
 
 void

src/backends/meta-stage.h

@@ -36,6 +36,7 @@ G_BEGIN_DECLS
 
 typedef struct _MetaStage      MetaStage;
 typedef struct _MetaStageClass MetaStageClass;
+typedef struct _MetaOverlay    MetaOverlay;
 
 struct _MetaStageClass
 {
@@ -51,7 +52,12 @@ GType             meta_stage_get_type                (void) G_GNUC_CONST;
 
 ClutterActor     *meta_stage_new                     (void);
 
-void meta_stage_set_cursor (MetaStage     *stage,
+MetaOverlay      *meta_stage_create_cursor_overlay   (MetaStage   *stage);
+void              meta_stage_remove_cursor_overlay   (MetaStage   *stage,
+						      MetaOverlay *overlay);
+
+void              meta_stage_update_cursor_overlay   (MetaStage     *stage,
+						      MetaOverlay   *overlay,
 						      CoglTexture   *texture,
 						      MetaRectangle *rect);