From e2a449a519e78814b4c2700940829994fd451a57 Mon Sep 17 00:00:00 2001
From: liyuqian <liyuqian@google.com>
Date: Fri, 22 Feb 2019 12:48:04 -0800
Subject: [PATCH] Move canvas clear after preroll (#7923)

This will reduce 1 render target switch when preroll paints some raster
cache.
---
 flow/compositor_context.cc | 5 +++++
 shell/common/rasterizer.cc | 4 ----
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/flow/compositor_context.cc b/flow/compositor_context.cc
index 8dc6883597999..30f1132818b2c 100644
--- a/flow/compositor_context.cc
+++ b/flow/compositor_context.cc
@@ -63,6 +63,11 @@ CompositorContext::ScopedFrame::~ScopedFrame() {
 bool CompositorContext::ScopedFrame::Raster(flow::LayerTree& layer_tree,
                                             bool ignore_raster_cache) {
   layer_tree.Preroll(*this, ignore_raster_cache);
+  // Clearing canvas after preroll reduces one render target switch when preroll
+  // paints some raster cache.
+  if (canvas()) {
+    canvas()->clear(SK_ColorTRANSPARENT);
+  }
   layer_tree.Paint(*this, ignore_raster_cache);
   return true;
 }
diff --git a/shell/common/rasterizer.cc b/shell/common/rasterizer.cc
index 48e8ea41aff00..39766a5877c99 100644
--- a/shell/common/rasterizer.cc
+++ b/shell/common/rasterizer.cc
@@ -181,10 +181,6 @@ bool Rasterizer::DrawToSurface(flow::LayerTree& layer_tree) {
       surface_->GetContext(), canvas, external_view_embedder,
       surface_->GetRootTransformation(), true);
 
-  if (canvas) {
-    canvas->clear(SK_ColorTRANSPARENT);
-  }
-
   if (compositor_frame && compositor_frame->Raster(layer_tree, false)) {
     frame->Submit();
     if (external_view_embedder != nullptr) {