window-actor: Handle geometry scale

Geometry scale is applied to each surface individually, using
Clutter scales, and not only this breaks subsurfaces, it also
pollutes the toolkit and makes the actor tree slightly too
fragile. If GNOME Shell mistakenly tries to set the actor scale
of any of these surfaces, for example, various artifacts might
happen.

Move geometry scale handling to MetaWindowActor. It is applied
as a child transform operation, so that the Clutter-managed
scale properties are left untouched.

In the future where the entirety of the window is managed by a
ClutterContent itself, the geometry scale will be applied
directly into the transform matrix of MetaWindowActor. However,
doing that now would break the various ClutterClones used by
GNOME Shell, so the child transform is an acceptable compromise
during this transition.

https://gitlab.gnome.org/GNOME/mutter/merge_requests/409

src/compositor/meta-surface-actor.c

@@ -22,6 +22,7 @@
 #include "clutter/clutter.h"
 #include "compositor/meta-cullable.h"
 #include "compositor/meta-shaped-texture-private.h"
+#include "compositor/meta-window-actor-private.h"
 #include "compositor/region-utils.h"
 #include "meta/meta-shaped-texture.h"
 
@@ -76,7 +77,6 @@ effective_unobscured_region (MetaSurfaceActor *surface_actor)
   return priv->unobscured_region;
 }
 
-
 static void
 set_unobscured_region (MetaSurfaceActor *surface_actor,
                        cairo_region_t   *unobscured_region)
@@ -250,18 +250,21 @@ meta_surface_actor_cull_out (MetaCullable   *cullable,
 
   if (opacity == 0xff)
     {
+      MetaWindowActor *window_actor;
       cairo_region_t *scaled_opaque_region;
       cairo_region_t *opaque_region;
-      double geometry_scale;
+      int geometry_scale = 1;
 
       opaque_region = meta_shaped_texture_get_opaque_region (priv->texture);
 
       if (!opaque_region)
         return;
 
-      clutter_actor_get_scale (CLUTTER_ACTOR (surface_actor),
-                               &geometry_scale,
-                               NULL);
+      window_actor =
+        meta_window_actor_from_actor (CLUTTER_ACTOR (surface_actor));
+      if (window_actor)
+        geometry_scale = meta_window_actor_get_geometry_scale (window_actor);
+
       scaled_opaque_region = meta_region_scale (opaque_region, geometry_scale);
 
       if (unobscured_region)

src/compositor/meta-window-actor-private.h

@@ -88,4 +88,9 @@ void meta_window_actor_assign_surface_actor (MetaWindowActor  *self,
 MetaWindowActor *meta_window_actor_from_window (MetaWindow *window);
 MetaWindowActor *meta_window_actor_from_actor (ClutterActor *actor);
 
+void meta_window_actor_set_geometry_scale (MetaWindowActor *window_actor,
+                                           int              geometry_scale);
+
+int meta_window_actor_get_geometry_scale (MetaWindowActor *window_actor);
+
 #endif /* META_WINDOW_ACTOR_PRIVATE_H */

src/compositor/meta-window-actor.c

@@ -81,6 +81,8 @@ typedef struct _MetaWindowActorPrivate
 
   MetaShadowMode    shadow_mode;
 
+  int geometry_scale;
+
   guint             size_changed_id;
 
   /*
@@ -252,6 +254,10 @@ meta_window_actor_class_init (MetaWindowActorClass *klass)
 static void
 meta_window_actor_init (MetaWindowActor *self)
 {
+  MetaWindowActorPrivate *priv =
+    meta_window_actor_get_instance_private (self);
+
+  priv->geometry_scale = 1;
 }
 
 static void
@@ -1891,6 +1897,34 @@ meta_window_actor_from_window (MetaWindow *window)
   return META_WINDOW_ACTOR (meta_window_get_compositor_private (window));
 }
 
+void
+meta_window_actor_set_geometry_scale (MetaWindowActor *window_actor,
+                                      int              geometry_scale)
+{
+  MetaWindowActorPrivate *priv =
+    meta_window_actor_get_instance_private (window_actor);
+  CoglMatrix child_transform;
+
+  if (priv->geometry_scale == geometry_scale)
+    return;
+
+  priv->geometry_scale = geometry_scale;
+
+  cogl_matrix_init_identity (&child_transform);
+  cogl_matrix_scale (&child_transform, geometry_scale, geometry_scale, 1);
+  clutter_actor_set_child_transform (CLUTTER_ACTOR (window_actor),
+                                     &child_transform);
+}
+
+int
+meta_window_actor_get_geometry_scale (MetaWindowActor *window_actor)
+{
+  MetaWindowActorPrivate *priv =
+    meta_window_actor_get_instance_private (window_actor);
+
+  return priv->geometry_scale;
+}
+
 static void
 meta_window_actor_get_frame_bounds (MetaScreenCastWindow *screen_cast_window,
                                     MetaRectangle        *bounds)

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

@@ -149,10 +149,6 @@ meta_wayland_actor_surface_real_sync_actor_state (MetaWaylandActorSurface *actor
 
   /* Wayland surface coordinate space -> stage coordinate space */
   geometry_scale = meta_wayland_actor_surface_get_geometry_scale (actor_surface);
-  clutter_actor_set_scale (CLUTTER_ACTOR (surface_actor),
-                           geometry_scale,
-                           geometry_scale);
-
   surface_rect = (cairo_rectangle_int_t) {
     .width = meta_wayland_surface_get_width (surface) * geometry_scale,
     .height = meta_wayland_surface_get_height (surface) * geometry_scale,

src/wayland/meta-wayland-subsurface.c

@@ -56,7 +56,6 @@ sync_actor_subsurface_state (MetaWaylandSurface *surface)
 {
   ClutterActor *actor = CLUTTER_ACTOR (meta_wayland_surface_get_actor (surface));
   MetaWindow *toplevel_window;
-  int geometry_scale;
   int x, y;
 
   toplevel_window = meta_wayland_surface_get_toplevel_window (surface);
@@ -66,9 +65,8 @@ sync_actor_subsurface_state (MetaWaylandSurface *surface)
   if (toplevel_window->client_type == META_WINDOW_CLIENT_TYPE_X11)
     return;
 
-  geometry_scale = meta_window_wayland_get_geometry_scale (toplevel_window);
-  x = (surface->offset_x + surface->sub.x) * geometry_scale;
-  y = (surface->offset_y + surface->sub.y) * geometry_scale;
+  x = surface->offset_x + surface->sub.x;
+  y = surface->offset_y + surface->sub.y;
 
   clutter_actor_set_position (actor, x, y);
 

src/wayland/meta-window-wayland.c

@@ -33,6 +33,7 @@
 #include "backends/meta-backend-private.h"
 #include "backends/meta-logical-monitor.h"
 #include "compositor/meta-surface-actor-wayland.h"
+#include "compositor/meta-window-actor-private.h"
 #include "core/boxes-private.h"
 #include "core/stack-tracker.h"
 #include "core/window-private.h"
@@ -69,6 +70,19 @@ struct _MetaWindowWaylandClass
 
 G_DEFINE_TYPE (MetaWindowWayland, meta_window_wayland, META_TYPE_WINDOW)
 
+static void
+set_geometry_scale_for_window (MetaWindowWayland *wl_window,
+                               int                geometry_scale)
+{
+  MetaWindowActor *window_actor;
+
+  wl_window->geometry_scale = geometry_scale;
+
+  window_actor = meta_window_actor_from_window (META_WINDOW (wl_window));
+  if (window_actor)
+    meta_window_actor_set_geometry_scale (window_actor, geometry_scale);
+}
+
 static int
 get_window_geometry_scale_for_logical_monitor (MetaLogicalMonitor *logical_monitor)
 {
@@ -526,8 +540,7 @@ meta_window_wayland_main_monitor_changed (MetaWindow               *window,
       meta_wayland_actor_surface_sync_actor_state (actor_surface);
     }
 
-  wl_window->geometry_scale = geometry_scale;
-
+  set_geometry_scale_for_window (wl_window, geometry_scale);
   meta_window_emit_size_changed (window);
 }
 
@@ -663,6 +676,8 @@ meta_window_wayland_new (MetaDisplay        *display,
                          MetaWaylandSurface *surface)
 {
   XWindowAttributes attrs = { 0 };
+  MetaWindowWayland *wl_window;
+  MetaWindow *window;
 
   /*
    * Set attributes used by _meta_window_shared_new, don't bother trying to fake
@@ -677,13 +692,18 @@ meta_window_wayland_new (MetaDisplay        *display,
   attrs.map_state = IsUnmapped;
   attrs.override_redirect = False;
 
-  return _meta_window_shared_new (display,
-                                  META_WINDOW_CLIENT_TYPE_WAYLAND,
-                                  surface,
-                                  None,
-                                  WithdrawnState,
-                                  META_COMP_EFFECT_CREATE,
-                                  &attrs);
+  window = _meta_window_shared_new (display,
+                                    META_WINDOW_CLIENT_TYPE_WAYLAND,
+                                    surface,
+                                    None,
+                                    WithdrawnState,
+                                    META_COMP_EFFECT_CREATE,
+                                    &attrs);
+
+  wl_window = META_WINDOW_WAYLAND (window);
+  set_geometry_scale_for_window (wl_window, wl_window->geometry_scale);
+
+  return window;
 }
 
 static gboolean