Change primary plane candidate to transparent when underlay is found

If the output surface is displayed as an overlay plane and there is a
video underlay, make the primary plane blend with the underlay such that
the transparent video hole in the primary plane allows the video to
show.

Bug: b/74998539
Test: Ran on device and verified video shows
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel
Change-Id: I01fd6c325dd2e93f7781fbbf1619bca402998217
Reviewed-on: https://chromium-review.googlesource.com/1005808Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Reviewed-by: Sergey Volk <servolk@chromium.org>
Commit-Queue: Daniel Nicoara <dnicoara@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550474}

components/viz/service/display/overlay_strategy_underlay_cast.cc

@@ -63,6 +63,14 @@ bool OverlayStrategyUnderlayCast::Attempt(
   }
 
   if (found_underlay) {
+    // If the primary plane shows up in the candidates list make sure it isn't
+    // opaque otherwise the video underlay won't be visible.
+    if (!candidate_list->empty()) {
+      DCHECK_EQ(1u, candidate_list->size());
+      DCHECK(candidate_list->front().use_output_surface_for_resource);
+      candidate_list->front().is_opaque = false;
+    }
+
     for (auto it = quad_list.begin(); it != quad_list.end(); ++it) {
       cc::OverlayCandidate candidate;
       if (!cc::OverlayCandidate::FromDrawQuad(

components/viz/service/display/overlay_unittest.cc

@@ -1883,6 +1883,37 @@ TEST_F(UnderlayCastTest, RoundContentBounds) {
   EXPECT_EQ(kOverlayRect, content_bounds_[0]);
 }
 
+TEST_F(UnderlayCastTest, PrimaryPlaneOverlayIsTransparentWithUnderlay) {
+  std::unique_ptr<RenderPass> pass = CreateRenderPass();
+  gfx::Rect output_rect = pass->output_rect;
+  CreateOpaqueQuadAt(resource_provider_.get(),
+                     pass->shared_quad_state_list.back(), pass.get(),
+                     output_rect, SK_ColorWHITE);
+
+  CreateCandidateQuadAt(
+      resource_provider_.get(), child_resource_provider_.get(),
+      pass->shared_quad_state_list.back(), pass.get(), kOverlayRect);
+
+  cc::OverlayCandidateList candidate_list;
+  cc::OverlayCandidate candidate;
+  candidate.use_output_surface_for_resource = true;
+  candidate.is_opaque = true;
+  candidate_list.push_back(candidate);
+
+  OverlayProcessor::FilterOperationsMap render_pass_filters;
+  OverlayProcessor::FilterOperationsMap render_pass_background_filters;
+  RenderPassList pass_list;
+  pass_list.push_back(std::move(pass));
+  overlay_processor_->ProcessForOverlays(
+      resource_provider_.get(), &pass_list, GetIdentityColorMatrix(),
+      render_pass_filters, render_pass_background_filters, &candidate_list,
+      nullptr, nullptr, &damage_rect_, &content_bounds_);
+
+  ASSERT_EQ(false, candidate_list[0].is_opaque);
+  EXPECT_EQ(1U, content_bounds_.size());
+  EXPECT_EQ(output_rect, content_bounds_[0]);
+}
+
 cc::OverlayCandidateList BackbufferOverlayList(
     const RenderPass* root_render_pass) {
   cc::OverlayCandidateList list;