wayland: Use a viewport for pointer surfaces

This should give us more flexibility for buffer size vs surface
size. Unfortunately, mutter doesn't play along.

gdk/wayland/gdkdevice-wayland-private.h

@@ -62,6 +62,7 @@ struct _GdkWaylandPointerData {
   uint32_t grab_time;
 
   struct wl_surface *pointer_surface;
+  struct wp_viewport *pointer_surface_viewport;
   guint cursor_is_default: 1;
   GdkCursor *cursor;
   guint cursor_timeout_id;

gdk/wayland/gdkdevice-wayland.c

@@ -310,7 +310,10 @@ gdk_wayland_device_update_surface_cursor (GdkDevice *device)
   if (buffer)
     {
       wl_surface_attach (pointer->pointer_surface, buffer, 0, 0);
-      wl_surface_set_buffer_scale (pointer->pointer_surface, scale);
+      if (pointer->pointer_surface_viewport)
+        wp_viewport_set_destination (pointer->pointer_surface_viewport, w, h);
+      else
+        wl_surface_set_buffer_scale (pointer->pointer_surface, scale);
       wl_surface_damage (pointer->pointer_surface,  0, 0, w, h);
       wl_surface_commit (pointer->pointer_surface);
     }

gdk/wayland/gdkseat-wayland.c

@@ -3878,6 +3878,7 @@ gdk_wayland_pointer_data_finalize (GdkWaylandPointerData *pointer)
   g_clear_object (&pointer->cursor);
   wl_surface_destroy (pointer->pointer_surface);
   g_slist_free (pointer->pointer_surface_outputs);
+  g_clear_pointer (&pointer->pointer_surface_viewport, wp_viewport_destroy);
 }
 
 static void
@@ -4241,6 +4242,8 @@ init_pointer_data (GdkWaylandPointerData *pointer_data,
   wl_surface_add_listener (pointer_data->pointer_surface,
                            &pointer_surface_listener,
                            logical_device);
+  if (display_wayland->viewporter)
+    pointer_data->pointer_surface_viewport = wp_viewporter_get_viewport (display_wayland->viewporter, pointer_data->pointer_surface);
 }
 
 void