cogl/onscreen: Pass damage regions unflipped

The other similar API all operate with the assumptions that (0,0) is at
the top left, so lets make damage regions behave this way too. Add a
helper to flip the rectangles, to make it a bit more convenient. It'll
be used in more places in a follow up.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/4103>

cogl/cogl/cogl-util.h

@@ -80,3 +80,23 @@ _cogl_util_one_at_a_time_mix (unsigned int hash)
 
     return hash;
 }
+
+static inline void
+cogl_rectangles_to_flipped_array (const int *rectangles,
+                                  int        n_rectangles,
+                                  int        height,
+                                  int       *rectangles_array)
+{
+  int i;
+
+  for (i = 0; i < n_rectangles; i++)
+    {
+      const int *rect = rectangles + 4 * i;
+      int *flip_rect = rectangles_array + 4 * i;
+
+      flip_rect[0] = rect[0];
+      flip_rect[1] = height - rect[1] - rect[3];
+      flip_rect[2] = rect[2];
+      flip_rect[3] = rect[3];
+    }
+}

cogl/cogl/winsys/cogl-onscreen-egl.c

@@ -256,15 +256,21 @@ cogl_onscreen_egl_queue_damage_region (CoglOnscreen *onscreen,
   CoglContext *context = cogl_framebuffer_get_context (framebuffer);
   CoglRenderer *renderer = context->display->renderer;
   CoglRendererEGL *egl_renderer = renderer->winsys;
+  int *egl_rectangles;
 
   g_return_if_fail (n_rectangles > 0);
 
   if (!egl_renderer->pf_eglSetDamageRegion)
     return;
 
+  egl_rectangles = g_alloca (n_rectangles * sizeof (int) * 4);
+  cogl_rectangles_to_flipped_array (rectangles, n_rectangles,
+                                    cogl_framebuffer_get_height (framebuffer),
+                                    egl_rectangles);
+
   if (egl_renderer->pf_eglSetDamageRegion (egl_renderer->edpy,
                                            priv->egl_surface,
-                                           rectangles,
+                                           egl_rectangles,
                                            n_rectangles) == EGL_FALSE)
     g_warning ("Error reported by eglSetDamageRegion");
 }

src/backends/meta-stage-impl.c

@@ -232,8 +232,7 @@ queue_damage_region (ClutterStageWindow *stage_window,
                                &rect);
 
       damage[i * 4] = rect.x;
-      /* y coordinate needs to be flipped for OpenGL */
+      damage[i * 4 + 1] = rect.y;
-      damage[i * 4 + 1] = fb_height - rect.y - rect.height;
       damage[i * 4 + 2] = rect.width;
       damage[i * 4 + 3] = rect.height;
     }