cc: Ignore certain quads that would otherwise block overlays

cc/output/overlay_strategy_single_on_top.cc

Index: cc/output/overlay_strategy_single_on_top.cc
diff --git a/cc/output/overlay_strategy_single_on_top.cc b/cc/output/overlay_strategy_single_on_top.cc
index 9a952068ecc8742c316cd50cc44632aef82714e9..0b583907bcb64b72db5d53bf600100ee69ffbdc9 100644
--- a/cc/output/overlay_strategy_single_on_top.cc
+++ b/cc/output/overlay_strategy_single_on_top.cc
@@ -119,6 +119,21 @@ bool OverlayStrategySingleOnTop::GetCandidateQuadInfo(
   return true;
 }
 
+bool OverlayStrategySingleOnTop::DoesQuadBlockOverlay(
+    const DrawQuad* draw_quad) {
+  if (draw_quad->material == DrawQuad::SOLID_COLOR) {
+    const SolidColorDrawQuad* solid_quad =
+        SolidColorDrawQuad::MaterialCast(draw_quad);
+    SkColor color = solid_quad->color;
+    float opacity = solid_quad->opacity();
+    float alpha = (SkColorGetA(color) * (1.0f / 255.0f)) * opacity;
+    // Ignore transparent solid color quads.
+    return !solid_quad->ShouldDrawWithBlending() ||

[danakj, 2015/02/04 18:42:32]

 !ShouldDrawWithBlending does not mean transparent like the comment suggests,
rather it means it is opaque and so no blending is needed.

[achaulk, 2015/02/04 22:20:30]

Done.

+           alpha >= std::numeric_limits<float>::epsilon();
+  }
+  return true;
+}
+
 bool OverlayStrategySingleOnTop::Attempt(
     RenderPassList* render_passes_in_draw_order,
     OverlayCandidateList* candidate_list) {
@@ -143,7 +158,8 @@ bool OverlayStrategySingleOnTop::Attempt(
            ++overlap_iter) {
         gfx::RectF overlap_rect = overlap_iter->rect;
         overlap_iter->quadTransform().TransformRect(&overlap_rect);
-        if (rect.Intersects(overlap_rect)) {
+        if (rect.Intersects(overlap_rect) &&
+            DoesQuadBlockOverlay(*overlap_iter)) {
           intersects = true;
           break;
         }