wayland: Check if state and size changed before calling move_resize()

The current implementation of the XdgSurface v6 protocol does not check
if the window changed before calling meta_window_wayland_move_resize().

The problem with this approach is that calling this function is a costly
operation since we enter the compositor side. In GNOME Shell case, it is
in JavaScript, which triggers a GJS trampoline. Calling this function on
every mouse movement is naturally as terrible as it could be - and is
exactly what happens now.

This commit adds the necessary checks to only call move_resize() when
the window actually changed, or when it needs to be updated.

https://bugzilla.gnome.org/show_bug.cgi?id=780292
Issue: #78

src/wayland/meta-wayland-legacy-xdg-shell.c

@@ -585,6 +585,17 @@ is_new_size_hints_valid (MetaWindow              *window,
           (new_max_height == 0 || new_min_height <= new_max_height));
 }
 
+static inline gboolean
+did_geometry_change (MetaWaylandZxdgSurfaceV6 *xdg_surface,
+                     MetaWaylandPendingState  *pending)
+{
+  MetaWaylandZxdgSurfaceV6Private *priv =
+    meta_wayland_zxdg_surface_v6_get_instance_private (xdg_surface);
+
+  return pending->has_new_geometry &&
+         !meta_rectangle_equal (&priv->geometry, &pending->new_geometry);
+}
+
 static void
 meta_wayland_zxdg_toplevel_v6_commit (MetaWaylandSurfaceRole  *surface_role,
                                       MetaWaylandPendingState *pending)
@@ -600,6 +611,11 @@ meta_wayland_zxdg_toplevel_v6_commit (MetaWaylandSurfaceRole  *surface_role,
     meta_wayland_surface_role_get_surface (surface_role);
   MetaWindow *window = surface->window;
   MetaRectangle window_geometry;
+  gboolean geometry_changed;
+
+  /* This check must happen before chaining up, otherwise the new geometry
+   * is applied and it'll always return FALSE. */
+  geometry_changed = did_geometry_change (xdg_surface, pending);
 
   surface_role_class =
     META_WAYLAND_SURFACE_ROLE_CLASS (meta_wayland_zxdg_toplevel_v6_parent_class);
@@ -618,7 +634,7 @@ meta_wayland_zxdg_toplevel_v6_commit (MetaWaylandSurfaceRole  *surface_role,
   if (!window)
     return;
 
-  if (pending->has_new_geometry)
+  if (geometry_changed || meta_window_wayland_needs_move_resize (window))
     {
       window_geometry =
         meta_wayland_zxdg_surface_v6_get_window_geometry (xdg_surface);

src/wayland/meta-wayland-xdg-shell.c

@@ -608,6 +608,17 @@ is_new_size_hints_valid (MetaWindow              *window,
           (new_max_height == 0 || new_min_height <= new_max_height));
 }
 
+static inline gboolean
+did_geometry_change (MetaWaylandXdgSurface   *xdg_surface,
+                     MetaWaylandPendingState *pending)
+{
+  MetaWaylandXdgSurfacePrivate *priv =
+    meta_wayland_xdg_surface_get_instance_private (xdg_surface);
+
+  return pending->has_new_geometry &&
+         !meta_rectangle_equal (&priv->geometry, &pending->new_geometry);
+}
+
 static void
 meta_wayland_xdg_toplevel_commit (MetaWaylandSurfaceRole  *surface_role,
                                   MetaWaylandPendingState *pending)
@@ -621,6 +632,7 @@ meta_wayland_xdg_toplevel_commit (MetaWaylandSurfaceRole  *surface_role,
     meta_wayland_surface_role_get_surface (surface_role);
   MetaWindow *window;
   MetaRectangle window_geometry;
+  gboolean geometry_changed;
 
   if (!surface->buffer_ref.buffer && xdg_surface_priv->first_buffer_attached)
     {
@@ -630,6 +642,10 @@ meta_wayland_xdg_toplevel_commit (MetaWaylandSurfaceRole  *surface_role,
 
   window = surface->window;
 
+  /* This check must happen before chaining up, otherwise the new geometry
+   * is applied and it'll always return FALSE. */
+  geometry_changed = did_geometry_change (xdg_surface, pending);
+
   surface_role_class =
     META_WAYLAND_SURFACE_ROLE_CLASS (meta_wayland_xdg_toplevel_parent_class);
   surface_role_class->commit (surface_role, pending);
@@ -643,7 +659,7 @@ meta_wayland_xdg_toplevel_commit (MetaWaylandSurfaceRole  *surface_role,
   if (!pending->newly_attached)
     return;
 
-  if (pending->has_new_geometry)
+  if (geometry_changed || meta_window_wayland_needs_move_resize (window))
     {
       window_geometry = meta_wayland_xdg_surface_get_window_geometry (xdg_surface);
       meta_window_wayland_move_resize (window,