cc: Partial tile update for one-copy raster.

cc/playback/raster_source.h

 // 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.
 
 #ifndef CC_PLAYBACK_RASTER_SOURCE_H_
 #define CC_PLAYBACK_RASTER_SOURCE_H_
 
 #include <vector>
 
 #include "base/memory/ref_counted.h"
@@ skipping 23 matching lines @@
     SkColor solid_color;
   };
 
   // Raster a subrect of this RasterSource into the given canvas. It is
   // assumed that contents_scale has already been applied to this canvas.
   // Writes the total number of pixels rasterized and the time spent
   // rasterizing to the stats if the respective pointer is not nullptr.
   // It is assumed that the canvas passed here will only be rasterized by
   // this raster source via this call.
   virtual void PlaybackToCanvas(SkCanvas* canvas,
-                                const gfx::Rect& canvas_rect,
+                                const gfx::Rect& canvas_bitmap_rect,
+                                const gfx::Rect& canvas_playback_rect,

[reveman, 2015/05/28 05:07:24]

Instead of adding another rect here, can we use SkCanvas::getBaseLayerSize() to
determine if playback_rect represents the whole canvas and optimized clear
functions can be used?

[danakj, 2015/05/28 18:54:46]

I don't like this, it really limits what the caller can do with the SkCanvas. It
could have a larger canvas (a 256x256 canvas?) for a smaller tile (an edge
tile?).

[reveman, 2015/05/29 14:50:26]

I'm sure you're right. It's just hard for me to see why canvas+rect is not
enough to satisfy both these use cases and canvas+rect+subrect is necessary. I
thought this was what PlaybackToSharedCanvas is already doing (playback into a
larger canvas that already contains some content) and I would have expected the
SharedCanvas version to be used for partial updates based on the description of
that function. Is the additional rect just so we can compute "bool
partial_update = canvas_bitmap_rect != canvas_playback_rect;" in
::PrepareForPlaybackToCanvas or also something else that I'm failing to see?

                                 float contents_scale) const = 0;
 
   // Similar to above, except that the canvas passed here can (or was already)
   // rasterized into by another raster source. That is, it is not safe to clear
   // the canvas or discard its underlying memory.
   virtual void PlaybackToSharedCanvas(SkCanvas* canvas,
                                       const gfx::Rect& canvas_rect,
                                       float contents_scale) const = 0;
 
   // Analyze to determine if the given rect at given scale is of solid color in
@@ skipping 52 matching lines @@
   RasterSource() {}
   virtual ~RasterSource() {}
 
  private:
   DISALLOW_COPY_AND_ASSIGN(RasterSource);
 };
 
 }  // namespace cc
 
 #endif  // CC_PLAYBACK_RASTER_SOURCE_H_