Optimize alpha software PictureDrawQuads.

skia/ext/opacity_draw_filter.h

+// Copyright (c) 2013 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 SKIA_EXT_OPACITY_DRAW_FILTER_H
+#define SKIA_EXT_OPACITY_DRAW_FILTER_H
+
+#include "base/values.h"
+#include "third_party/skia/include/core/SkDrawFilter.h"
+
+class SkPaint;
+
+namespace skia {
+
+// This filter allows setting an opacity on every draw call to a canvas, and to
+// disable image filtering. Note that setting opacity with this is only correct
+// when there are no overlapping draw calls (as this doesn't allocate a bitmap

[enne (OOO), 2013/08/28 20:08:42]

It's also only correct when draw calls are all opaque (as this clobbers the
alpha) and when there aren't nested SaveLayer calls (I think?)

[aelias_OOO_until_Jul13, 2013/08/28 20:23:00]

I made the comment clearer.

+// to collapse them together before blending the result against the
+// backbuffer).
+class SK_API OpacityDrawFilter : public SkDrawFilter {
+ public:
+  OpacityDrawFilter(float opacity, bool disable_image_filtering);
+  virtual ~OpacityDrawFilter();
+  virtual bool filter(SkPaint* paint, SkDrawFilter::Type type) OVERRIDE;
+
+ private:
+  int alpha_;
+  bool disable_image_filtering_;
+};
+
+}  // namespace skia
+
+#endif  // SKIA_EXT_OPACITY_DRAW_FILTER_H
+