Add luminance mask transfer modes.

include/effects/SkLumaXfermode.h

+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkLumaXfermode_DEFINED
+#define SkLumaXfermode_DEFINED
+
+#include "SkXfermode.h"
+
+/**
+ *  Luminance mask transfer, as defined in
+ *  http://www.w3.org/TR/SVG/masking.html#Masking
+ *  http://www.w3.org/TR/css-masking/#MaskValues
+ *
+ *  The luminance-to-alpha function is applied before performing a standard
+ *  SrcIn/DstIn xfer:
+ *
+ *    luma(C) = (0.2125 * C.r + 0.7154 * C.g + 0.0721 * C.b) * C.a
+ *
+ *  (where C is un-premultiplied)
+ */
+class SK_API SkLumaMaskXfermode : public SkXfermode {
+public:
+    /** Return an SkLumaMaskXfermode object for the specified submode.
+     *
+     *  Only kSrcIn_Mode and kDstIn_Mode are supported - for everything else,
+     *  the factory returns NULL.
+     */
+    static SkXfermode* Create(SkXfermode::Mode);
+
+    virtual SkPMColor xferColor(SkPMColor, SkPMColor) const SK_OVERRIDE;
+    virtual void xfer32(SkPMColor dst[], const SkPMColor src[], int count,
+                        const SkAlpha aa[]) const SK_OVERRIDE;
+
+    SK_DEVELOPER_TO_STRING()
+    SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkLumaMaskXfermode)
+
+#if SK_SUPPORT_GPU
+    virtual bool asNewEffectOrCoeff(GrContext*, GrEffectRef**, Coeff*, Coeff*,
+                                    GrTexture*) const SK_OVERRIDE;
+#endif
+
+protected:
+    SkLumaMaskXfermode(SkFlattenableReadBuffer&);
+    virtual void flatten(SkFlattenableWriteBuffer&) const SK_OVERRIDE;
+
+private:
+    SkLumaMaskXfermode(SkXfermode::Mode);
+
+    const SkXfermode::Mode fMode;
+
+    typedef SkXfermode INHERITED;
+};
+
+#endif