Use SkLayerDrawLooper::Builder to construct SkLayerDrawLooper.

Source/platform/graphics/DrawLooper.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 14 matching lines @@
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef DrawLooper_h
 #define DrawLooper_h
 
 #include "platform/PlatformExport.h"
+#include "third_party/skia/include/effects/SkLayerDrawLooper.h"
 #include "wtf/Noncopyable.h"
 #include "wtf/RefPtr.h"
 
 class SkDrawLooper;
-class SkLayerDrawLooper;
 
 namespace WebCore {
 
 class Color;
 class FloatSize;
 
 class PLATFORM_EXPORT DrawLooper {
     // Implementing the copy constructor properly would require writing code to
     // copy the underlying SkDrawLooper.
     WTF_MAKE_NONCOPYABLE(DrawLooper);
 
 public:
     enum ShadowTransformMode {
         ShadowRespectsTransforms,
         ShadowIgnoresTransforms
     };
     enum ShadowAlphaMode {
         ShadowRespectsAlpha,
         ShadowIgnoresAlpha
     };
 
     DrawLooper();
     ~DrawLooper();
 
     // Callees should not modify this looper other than to iterate over it.
     // A downcast to SkLayerDrawLooper* is tantamount to a const_cast.
-    SkDrawLooper* skDrawLooper() const;
+    SkDrawLooper* skDrawLooper();

[jbroman, 2014/02/24 15:23:33]

This method now destroys the WebCore::DrawLooper as well, and it's not at all
obvious that it has this effect. If, for example, a callee tried to keep a
DrawLooper instance around, this would not behave as one would expect.

I like that Skia is making draw loopers immutable, but I think the
platform/graphics/ API should make this clear. My suggestion would be to mirror
the change in the Skia API, and call this class "DrawLooperBuilder" or similar,
and rename this something that makes it obvious that it resets the builder, like
the method SkLayerDrawLooper::Builder has.

It could either return an SkDrawLooper* or a new WebCore::DrawLooper type (which
would be a simple wrapper if we don't want to expose Skia types to core/).

[Dominik Grewe, 2014/02/24 15:47:28]

Makes sense. How about replicating the structure in Skia, i.e. keep the
'DrawLooper' class but move all the add* methods to an inner 'Builder' class
with a 'detachLooper()' method?

 
     void addUnmodifiedContent();
     void addShadow(const FloatSize& offset, float blur, const Color&,
         ShadowTransformMode = ShadowRespectsTransforms,
         ShadowAlphaMode = ShadowRespectsAlpha);
 
 private:
-    RefPtr<SkLayerDrawLooper> m_skDrawLooper;
+    SkLayerDrawLooper::Builder m_skDrawLooperBuilder;
 };
 
 } // namespace WebCore
 
 #endif // DrawLooper_h