cc: Partial draw without partial swap support.

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 <stddef.h>
 
 #include <unordered_map>
 #include <utility>
@@ skipping 319 matching lines @@
     frames_since_using_dc_layers_ = 0;
   } else if (++frames_since_using_dc_layers_ >=
              kNumberOfFramesBeforeDisablingDCLayers) {
     using_dc_layers_ = false;
   }
   if (was_using_dc_layers != using_dc_layers_) {
     current_frame()->root_damage_rect =
         current_frame()->root_render_pass->output_rect;
   }
 
+  allow_partial_draw_ =
+      use_partial_swap_ ||
+      output_surface_->CanPartialDraw(current_frame()->root_damage_rect);
+
   // We can skip all drawing if the damage rect is now empty.
   bool skip_drawing_root_render_pass =
       current_frame()->root_damage_rect.IsEmpty() && allow_empty_swap_;
 
-  // If we have to draw but don't support partial swap, the whole output should
-  // be considered damaged.
-  if (!skip_drawing_root_render_pass && !use_partial_swap_)
-    current_frame()->root_damage_rect = root_render_pass->output_rect;
-
   if (skip_drawing_root_render_pass) {
     // If any of the overlays is the output surface, then ensure that the
     // backbuffer be allocated (allocation of the backbuffer is a side-effect
     // of BindFramebufferToOutputSurface).
     for (auto& overlay : current_frame()->overlay_list) {
       if (overlay.use_output_surface_for_resource) {
         BindFramebufferToOutputSurface();
         break;
       }
     }
@@ skipping 166 matching lines @@
 
   const gfx::Rect surface_rect_in_draw_space = OutputSurfaceRectInDrawSpace();
   gfx::Rect render_pass_scissor_in_draw_space = surface_rect_in_draw_space;
 
   if (current_frame()->current_render_pass ==
       current_frame()->root_render_pass) {
     render_pass_scissor_in_draw_space.Intersect(
         DeviceViewportRectInDrawSpace());
   }
 
-  if (use_partial_swap_) {
+  if (allow_partial_draw_) {
     render_pass_scissor_in_draw_space.Intersect(
         current_frame()->ComputeScissorRectForRenderPass());
   }
 
   bool is_root_render_pass =
       current_frame()->current_render_pass == current_frame()->root_render_pass;
 
   bool render_pass_is_clipped =
       !render_pass_scissor_in_draw_space.Contains(surface_rect_in_draw_space);
 
@@ skipping 117 matching lines @@
 gfx::Size DirectRenderer::RenderPassTextureSize(const RenderPass* render_pass) {
   return render_pass->output_rect.size();
 }
 
 void DirectRenderer::SetCurrentFrameForTesting(const DrawingFrame& frame) {
   current_frame_valid_ = true;
   current_frame_ = frame;
 }
 
 }  // namespace cc