Avoid Copying damage rect when using Overlays

cc/output/direct_renderer.cc

Index: cc/output/direct_renderer.cc
diff --git a/cc/output/direct_renderer.cc b/cc/output/direct_renderer.cc
index f98151833e040baeeb7b81076c53d949d0307a2c..098137740bae2da2684bbf1ce196fae1492968a8 100644
--- a/cc/output/direct_renderer.cc
+++ b/cc/output/direct_renderer.cc
@@ -241,6 +241,12 @@ void DirectRenderer::DrawFrame(RenderPassList* render_passes_in_draw_order,
   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) {