Implement SkXfermode image filter

include/effects/SkXfermodeImageFilter.h

 /*
- * Copyright 2012 The Android Open Source Project
+ * Copyright 2013 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
-#ifndef SkBlendImageFilter_DEFINED
-#define SkBlendImageFilter_DEFINED
+#ifndef SkXfermodeImageFilter_DEFINED
+#define SkXfermodeImageFilter_DEFINED
 
 #include "SkImageFilter.h"
-#include "SkBitmap.h"
 
-class SK_API SkBlendImageFilter : public SkImageFilter {
+class SkBitmap;
+class SkXfermode;
+
+class SK_API SkXfermodeImageFilter : public SkImageFilter {
+    /**
+     * This filter takes an xfermode, and uses it to composite the foreground
+     * over the background.  If foreground or background is NULL, the input
+     * bitmap (src) is used instead.
+      */
+
 public:
-    enum Mode {
-      kNormal_Mode,
-      kMultiply_Mode,
-      kScreen_Mode,
-      kDarken_Mode,
-      kLighten_Mode,
-    };
-    SkBlendImageFilter(Mode mode, SkImageFilter* background, SkImageFilter* foreground = NULL);
+    SkXfermodeImageFilter(SkXfermode* mode, SkImageFilter* background, SkImageFilter* foreground = NULL);
 
-    ~SkBlendImageFilter();
+    virtual ~SkXfermodeImageFilter();
 
-    SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkBlendImageFilter)
+    SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkXfermodeImageFilter)
 
     virtual bool onFilterImage(Proxy* proxy,
                                const SkBitmap& src,
                                const SkMatrix& ctm,
                                SkBitmap* dst,
                                SkIPoint* offset) SK_OVERRIDE;
 #if SK_SUPPORT_GPU
     virtual bool canFilterImageGPU() const SK_OVERRIDE { return true; }
     virtual bool filterImageGPU(Proxy* proxy, const SkBitmap& src, SkBitmap* result) SK_OVERRIDE;
 #endif
 
 protected:
-    explicit SkBlendImageFilter(SkFlattenableReadBuffer& buffer);
+    explicit SkXfermodeImageFilter(SkFlattenableReadBuffer& buffer);
     virtual void flatten(SkFlattenableWriteBuffer&) const SK_OVERRIDE;
 
 private:
-    Mode fMode;
+    SkXfermode* fMode;
     typedef SkImageFilter INHERITED;
-    SkImageFilter* getBackgroundInput() { return getInput(0); }
-    SkImageFilter* getForegroundInput() { return getInput(1); }
 };
 
 #endif