Revert[8] "replace SkXfermode obj with SkBlendMode enum in paints"

include/core/SkBlendMode.h

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkBlendMode_DEFINED
+#define SkBlendMode_DEFINED
+
+enum class SkBlendMode {
+    kClear,    //!< [0, 0]
+    kSrc,      //!< [Sa, Sc]
+    kDst,      //!< [Da, Dc]
+    kSrcOver,  //!< [Sa + Da * (1 - Sa), Sc + Dc * (1 - Sa)]
+    kDstOver,  //!< [Da + Sa * (1 - Da), Dc + Sc * (1 - Da)]
+    kSrcIn,    //!< [Sa * Da, Sc * Da]
+    kDstIn,    //!< [Da * Sa, Dc * Sa]
+    kSrcOut,   //!< [Sa * (1 - Da), Sc * (1 - Da)]
+    kDstOut,   //!< [Da * (1 - Sa), Dc * (1 - Sa)]
+    kSrcATop,  //!< [Da, Sc * Da + Dc * (1 - Sa)]
+    kDstATop,  //!< [Sa, Dc * Sa + Sc * (1 - Da)]
+    kXor,      //!< [Sa + Da - 2 * Sa * Da, Sc * (1 - Da) + Dc * (1 - Sa)]
+    kPlus,     //!< [Sa + Da, Sc + Dc]
+    kModulate, // multiplies all components (= alpha and color)
+
+    // Following blend modes are defined in the CSS Compositing standard:
+    // https://dvcs.w3.org/hg/FXTF/rawfile/tip/compositing/index.html#blending
+    kScreen,
+    kLastCoeffMode = kScreen,
+
+    kOverlay,
+    kDarken,
+    kLighten,
+    kColorDodge,
+    kColorBurn,
+    kHardLight,
+    kSoftLight,
+    kDifference,
+    kExclusion,
+    kMultiply,
+    kLastSeparableMode = kMultiply,
+
+    kHue,
+    kSaturation,
+    kColor,
+    kLuminosity,
+    kLastMode = kLuminosity
+};
+
+#endif