Make CanvasPainter raster directly to an SkBitmap

ui/compositor/canvas_painter.h

 // Copyright 2015 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 UI_COMPOSITOR_CANVAS_PAINTER_H_
 #define UI_COMPOSITOR_CANVAS_PAINTER_H_
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "ui/compositor/compositor_export.h"
 #include "ui/compositor/paint_context.h"
 #include "ui/gfx/geometry/rect.h"
 
 namespace cc {
 class DisplayItemList;
 }
 
-namespace gfx {
-class Canvas;
-}
-
 namespace ui {
 
-// This class provides a simple helper for painting directly to a bitmap
-// backed canvas (for painting use-cases other than compositing). After
-// constructing an instance of a CanvasPainter, the context() can be used
-// to do painting using the normal composited paint paths. When
-// the painter is destroyed, any painting done with the context() will be
-// rastered into the canvas.
+// This class provides a simple helper for rasterizing from a PaintContext
+// interface directly into a bitmap.  After constructing an instance of a
+// CanvasPainter, the context() can be used to do painting using the normal
+// composited paint paths.  When the painter is destroyed, any painting done
+// with the context() will be rastered into the provided output bitmap.
+//
+// TODO(enne): rename this class to be PaintContextRasterizer or some such.
 class COMPOSITOR_EXPORT CanvasPainter {
  public:
-  CanvasPainter(gfx::Canvas* canvas, float raster_scale_factor);
+  CanvasPainter(SkBitmap* output,

[danakj, 2017/02/14 21:37:26]

In blink at least this type of thing should be an SkCanvas cuz they generate
SkPictures sometimes, but I don't think UI does so u can go right to SkBitmap
here I guess.

+                gfx::Size paint_size,

[danakj, 2017/02/14 21:37:26]

const&

+                float raster_scale,
+                SkColor clear_color);
   ~CanvasPainter();
 
   const PaintContext& context() const { return context_; }
 
  private:
-  gfx::Canvas* const canvas_;
-  const float raster_scale_factor_;
-  const gfx::Rect rect_;
+  SkBitmap* const output_;
+  const gfx::Size paint_size_;
+  SkColor clear_color_;

[danakj, 2017/02/14 21:37:26]

const?

   scoped_refptr<cc::DisplayItemList> list_;
   PaintContext context_;
 
   DISALLOW_COPY_AND_ASSIGN(CanvasPainter);
 };
 
 }  // namespace ui
 
 #endif  // UI_COMPOSITOR_CANVAS_PAINTER_H_