Reset the state of the previous frame if overlay processing is skipped.

cc/output/overlay_processor.cc

 // Copyright 2014 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/overlay_processor.h"
 
 #include "cc/output/dc_layer_overlay.h"
 #include "cc/output/output_surface.h"
 #include "cc/output/overlay_strategy_single_on_top.h"
 #include "cc/output/overlay_strategy_underlay.h"
@@ skipping 125 matching lines @@
     // If overlay processing was skipped for a frame there's no way to be sure
     // of the state of the previous frame, so reset.
     previous_frame_underlay_rect_ = gfx::Rect();
     return;
   }
 
   // First attempt to process for CALayers.
   if (ProcessForCALayers(resource_provider, render_pass, render_pass_filters,
                          render_pass_background_filters, candidates,
                          ca_layer_overlays, damage_rect)) {
+    previous_frame_underlay_rect_ = gfx::Rect();

[liberato (no reviews please), 2017/04/26 18:40:31]

clearing it seems to be the default (and safe) action.  to avoid having this
happen the next time somebody adds an early-out, maybe do this instead near the
top of this fn:

gfx::Rect previous_frame_underlay_rect = previous_frame_underlay_rect_;
previous_frame_underlay_rect_ = gfx::Rect();

then, pass the copy as an argument to UpdateDamageRect, rather than having it
look at the original.  it can update |previous...rect_| if it wants to.

at least, i think that @198 is the only place where we update this to a
non-empty value.

[watk, 2017/04/26 19:20:04]

+1

[AndyWu, 2017/04/26 20:40:53]

Done, thanks for your suggestion.

     return;
   }
 
   if (ProcessForDCLayers(resource_provider, render_pass, render_pass_filters,
                          render_pass_background_filters, candidates,
                          dc_layer_overlays, damage_rect)) {
+    previous_frame_underlay_rect_ = gfx::Rect();
     return;
   }
 
   // Only if that fails, attempt hardware overlay strategies.
   for (const auto& strategy : strategies_) {
     if (!strategy->Attempt(resource_provider, render_pass, candidates,
                            content_bounds))
       continue;
 
     UpdateDamageRect(candidates, damage_rect);
     return;
   }
+
+  previous_frame_underlay_rect_ = gfx::Rect();
 }
 
 // Subtract on-top overlays from the damage rect, unless the overlays use
 // the backbuffer as their content (in which case, add their combined rect
 // back to the damage at the end).
 // Also subtract unoccluded underlays from the damage rect if we know that the
 // same underlay was scheduled on the previous frame. If the renderer decides
 // not to swap the framebuffer there will still be a transparent hole in the
 // previous frame. This only handles the common case of a single underlay quad
 // for fullscreen video.
@@ skipping 16 matching lines @@
   }
 
   if (this_frame_underlay_rect == previous_frame_underlay_rect_)
     damage_rect->Subtract(this_frame_underlay_rect);
   previous_frame_underlay_rect_ = this_frame_underlay_rect;
 
   damage_rect->Union(output_surface_overlay_damage_rect);
 }
 
 }  // namespace cc