Avoid Copying damage rect when using Overlays

cc/output/direct_renderer.cc

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/output/direct_renderer.h"
 
 #include <utility>
 #include <vector>
 
 #include "base/containers/hash_tables.h"
@@ skipping 223 matching lines @@
     output_surface_plane.use_output_surface_for_resource = true;
     output_surface_plane.overlay_handled = true;
     frame.overlay_list.push_back(output_surface_plane);
   }
 
   // If we have any copy requests, we can't remove any quads for overlays,
   // otherwise the framebuffer will be missing the overlay contents.
   if (root_render_pass->copy_requests.empty()) {
     overlay_processor_->ProcessForOverlays(render_passes_in_draw_order,
                                            &frame.overlay_list);
+    for (const OverlayCandidate& overlay : frame.overlay_list) {
+      if (overlay.plane_z_order <= 0)
+        continue;
+
+      frame.root_damage_rect.Subtract(ToNearestRect(overlay.display_rect));

[piman, 2015/10/08 22:51:31]

That's only true if the overlay is opaque. Also, ToNearestRect looks a bit
sloppy, could cause issues for non-screen-aligned rects. It seems like this
should really be handled by OverlayProcessor, or even the various
OverlayStrategy which have a clearer grasp on the exact intent. I'm comfortable
passing the damage rect down to there.

[kalyank, 2015/10/12 22:58:45]

Moved this to processor now. I have added a bool to candidate to know if it
needs blending. If blending is needed, we dont subtract the candidates display
rect from root damage rect.

Reg ToNearestRect, which should be the right conversion API ?

[kalyank, 2015/10/12 22:58:45]

Acknowledged.

[piman, 2015/10/20 01:49:19]

Whatever damage you remove must be fully covered by the opaque overlay. So that
means the opaque overlay rect must enclose the removed rect. So it seems like
ToEnclosedRect is the right conservative choice?

+    }
   }
 
   for (size_t i = 0; i < render_passes_in_draw_order->size(); ++i) {
     RenderPass* pass = render_passes_in_draw_order->at(i);
     DrawRenderPass(&frame, pass);
 
     for (ScopedPtrVector<CopyOutputRequest>::iterator it =
              pass->copy_requests.begin();
          it != pass->copy_requests.end();
          ++it) {
@@ skipping 281 matching lines @@
   ScopedResource* texture = render_pass_textures_.get(id);
   return texture && texture->id();
 }
 
 // static
 gfx::Size DirectRenderer::RenderPassTextureSize(const RenderPass* render_pass) {
   return render_pass->output_rect.size();
 }
 
 }  // namespace cc