stage-impl: Transform damage region before queuing

In order to queue the right values for transformed `MetaRendererView`s.

While on it ensure we query the framebuffers width/height only once,
saving some cpu cycles.

Closes https://gitlab.gnome.org/GNOME/mutter/-/issues/2557

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2860>

(cherry picked from commit 943fcc7c1a5e9b7ca7cf815c9adbd35de6ab14b2)

2 files changed, 15 insertions, 2 deletions

diff --git a/cogl/cogl/cogl-onscreen.h b/cogl/cogl/cogl-onscreen.h
index 677893493..ad71fa893 100644
--- a/cogl/cogl/cogl-onscreen.h
+++ b/cogl/cogl/cogl-onscreen.h
@@ -242,6 +242,9 @@ cogl_onscreen_get_buffer_age (CoglOnscreen *onscreen);
  * This immediately queues state to OpenGL that will be used for the
  * next swap.
  * This needs to be called every frame.
+ *
+ * The expected values are independent of any viewport transforms applied to
+ * the framebuffer.
  */
 COGL_EXPORT void
 cogl_onscreen_queue_damage_region (CoglOnscreen *onscreen,
diff --git a/src/backends/meta-stage-impl.c b/src/backends/meta-stage-impl.c
index ca6f1f44f..25d240d81 100644
--- a/src/backends/meta-stage-impl.c
+++ b/src/backends/meta-stage-impl.c
@@ -214,6 +214,8 @@ queue_damage_region (ClutterStageWindow *stage_window,
   g_autofree int *freeme = NULL;
   CoglFramebuffer *framebuffer;
   CoglOnscreen *onscreen;
+  int fb_width;
+  int fb_height;
 
   if (cairo_region_is_empty (damage_region))
     return;
@@ -223,6 +225,8 @@ queue_damage_region (ClutterStageWindow *stage_window,
     return;
 
   onscreen = COGL_ONSCREEN (framebuffer);
+  fb_width = cogl_framebuffer_get_width (framebuffer);
+  fb_height = cogl_framebuffer_get_height (framebuffer);
 
   n_rects = cairo_region_num_rectangles (damage_region);
 
@@ -234,12 +238,18 @@ queue_damage_region (ClutterStageWindow *stage_window,
   for (i = 0; i < n_rects; i++)
     {
       cairo_rectangle_int_t rect;
-      int height = cogl_framebuffer_get_height (framebuffer);
 
       cairo_region_get_rectangle (damage_region, i, &rect);
+
+      clutter_stage_view_transform_rect_to_onscreen (stage_view,
+                                                     &rect,
+                                                     fb_width,
+                                                     fb_height,
+                                                     &rect);
+
       damage[i * 4] = rect.x;
       /* y coordinate needs to be flipped for OpenGL */
-      damage[i * 4 + 1] = height - rect.y - rect.height;
+      damage[i * 4 + 1] = fb_height - rect.y - rect.height;
       damage[i * 4 + 2] = rect.width;
       damage[i * 4 + 3] = rect.height;
     }