Optimize alpha software PictureDrawQuads.

skia/ext/opacity_draw_filter.cc

+// 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.
+
+#include "skia/ext/opacity_draw_filter.h"
+#include "third_party/skia/include/core/SkPaint.h"
+
+namespace skia {
+
+OpacityDrawFilter::OpacityDrawFilter(float opacity, bool disable_image_filtering)
+    : opacity_(opacity), disable_image_filtering_(disable_image_filtering) {}
+
+OpacityDrawFilter::~OpacityDrawFilter() {}
+
+bool OpacityDrawFilter::filter(SkPaint* paint, Type type) {
+  if (opacity_ != 1.f)
+    paint->setAlpha(SkScalarRound(opacity_ * 255));

[tomhudson, 2013/08/28 14:55:18]

(Maybe arguing against my comment in the header)

Should we be setting alpha, or multiplying alpha?

I want to say that if we're setting you should omit the if for clarity, but
setting alpha is just heavyweight enough that it might be a performance loss, at
least if Android's ChromeView ever links with system Skia.

[aelias_OOO_until_Jul13, 2013/08/28 18:50:35]

There's an argument for multiplying, but for now I'm setting alpha because
that's what the classic WebView implementation did.  (You can see the code at
http://goo.gl/ZtQjjU ).

+  if (disable_image_filtering_)
+    paint->setFilterLevel(SkPaint::kNone_FilterLevel);
+  return true;
+}
+
+}  // namespace skia
+
+