[mutter] backends: Enable partial update on clipped redraws

[Marge Bot <marge-bot src gnome org>]

commit 577c4711e15650a79cbaf8e1001d1e7482241d38
Author: Erico Nunes <nunes erico gmail com>
Date:   Wed Sep 22 22:26:23 2021 +0200

    backends: Enable partial update on clipped redraws
    
    Mutter already calculates and tracks the damage rectangles to redraw
    only areas of the screen that change since the last time a buffer was
    used.
    This patch extends this by using the EGL_KHR_partial_update extension to
    inform the GPU in advance that only those areas will be changed, which
    may allow for further optimization.
    
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2023>

 src/backends/meta-stage-impl.c | 44 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)
---
diff --git a/src/backends/meta-stage-impl.c b/src/backends/meta-stage-impl.c
index 28534ec812..2990c89779 100644
--- a/src/backends/meta-stage-impl.c
+++ b/src/backends/meta-stage-impl.c
@@ -199,6 +199,48 @@ paint_damage_region (ClutterStageWindow *stage_window,
   cogl_framebuffer_pop_matrix (framebuffer);
 }
 
+static void
+queue_damage_region (ClutterStageWindow *stage_window,
+                     ClutterStageView   *stage_view,
+                     cairo_region_t     *damage_region)
+{
+  int *damage, n_rects, i;
+  g_autofree int *freeme = NULL;
+  CoglFramebuffer *framebuffer;
+  CoglOnscreen *onscreen;
+
+  if (cairo_region_is_empty (damage_region))
+    return;
+
+  framebuffer = clutter_stage_view_get_onscreen (stage_view);
+  if (!COGL_IS_ONSCREEN (framebuffer))
+    return;
+
+  onscreen = COGL_ONSCREEN (framebuffer);
+
+  n_rects = cairo_region_num_rectangles (damage_region);
+
+  if (n_rects < MAX_STACK_RECTS)
+    damage = g_newa (int, n_rects * 4);
+  else
+    damage = freeme = g_new (int, n_rects * 4);
+
+  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);
+      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 + 2] = rect.width;
+      damage[i * 4 + 3] = rect.height;
+    }
+
+  cogl_onscreen_queue_damage_region (onscreen, damage, n_rects);
+}
+
 static void
 swap_framebuffer (ClutterStageWindow *stage_window,
                   ClutterStageView   *stage_view,
@@ -550,6 +592,8 @@ meta_stage_impl_redraw_view_primary (MetaStageImpl    *stage_impl,
     }
   else if (use_clipped_redraw)
     {
+      queue_damage_region (stage_window, stage_view, fb_clip_region);
+
       cogl_framebuffer_push_region_clip (fb, fb_clip_region);
 
       paint_stage (stage_impl, stage_view, redraw_clip);