Add canvas blending modes under a runtime flag

Source/core/platform/graphics/skia/SkiaUtils.cpp

 /*
  * Copyright (c) 2006,2007,2008, 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 43 matching lines @@
     { CompositeSourceAtop,      SkXfermode::kSrcATop_Mode },
     { CompositeDestinationOver, SkXfermode::kDstOver_Mode },
     { CompositeDestinationIn,   SkXfermode::kDstIn_Mode },
     { CompositeDestinationOut,  SkXfermode::kDstOut_Mode },
     { CompositeDestinationAtop, SkXfermode::kDstATop_Mode },
     { CompositeXOR,             SkXfermode::kXor_Mode },
     { CompositePlusDarker,      SkXfermode::kDarken_Mode },
     { CompositePlusLighter,     SkXfermode::kPlus_Mode }
 };
 
-SkXfermode::Mode WebCoreCompositeToSkiaComposite(CompositeOperator op)
+// keep this array in sync with BlendMode enum in GraphicsTypes.h

[eseidel, 2013/05/08 19:34:44]

We can COMPILE_ASSERT That these match, no?

[rosca, 2013/05/08 21:37:17]

Yes, we can compile_assert, but I'm not sure it worths, these values are not
likely to change in the future.

+static const uint8_t gMapBlendOpsToXfermodeModes[] = {
+    SkXfermode::kClear_Mode, // BlendModeNormal
+    SkXfermode::kMultiply_Mode, // BlendModeMultiply
+    SkXfermode::kScreen_Mode, // BlendModeScreen
+    SkXfermode::kOverlay_Mode, // BlendModeOverlay
+    SkXfermode::kDarken_Mode, // BlendModeDarken
+    SkXfermode::kLighten_Mode, // BlendModeLighten
+    SkXfermode::kColorDodge_Mode, // BlendModeColorDodge
+    SkXfermode::kColorBurn_Mode, // BlendModeColorBurn
+    SkXfermode::kHardLight_Mode, // BlendModeHardLight
+    SkXfermode::kSoftLight_Mode, // BlendModeSoftLight
+    SkXfermode::kDifference_Mode, // BlendModeDifference
+    SkXfermode::kExclusion_Mode, // BlendModeExclusion
+    SkXfermode::kHue_Mode, // BlendModeHue
+    SkXfermode::kSaturation_Mode, // BlendModeSaturation
+    SkXfermode::kColor_Mode, // BlendModeColor
+    SkXfermode::kLuminosity_Mode // BlendModeLuminosity
+};
+
+SkXfermode::Mode WebCoreCompositeToSkiaComposite(CompositeOperator op, BlendMode blendMode)
 {
+    if (blendMode != BlendModeNormal) {
+        if ((uint8_t)blendMode >= SK_ARRAY_COUNT(gMapBlendOpsToXfermodeModes)) {
+            SkDEBUGF(("GraphicsContext::setPlatformCompositeOperation unknown BlendMode %d\n", blendMode));
+            return SkXfermode::kSrcOver_Mode;
+        }
+        return (SkXfermode::Mode)gMapBlendOpsToXfermodeModes[(uint8_t)blendMode];
+    }
+
     const CompositOpToXfermodeMode* table = gMapCompositOpsToXfermodeModes;
     
     for (unsigned i = 0; i < SK_ARRAY_COUNT(gMapCompositOpsToXfermodeModes); i++) {
         if (table[i].mCompositOp == op)
             return (SkXfermode::Mode)table[i].m_xfermodeMode;
     }
 
     SkDEBUGF(("GraphicsContext::setPlatformCompositeOperation unknown CompositeOperator %d\n", op));
     return SkXfermode::kSrcOver_Mode; // fall-back
 }
@@ skipping 84 matching lines @@
 
 GraphicsContext* scratchContext()
 {
     static ImageBuffer* scratch = ImageBuffer::create(IntSize(1, 1)).leakPtr();
     // We don't bother checking for failure creating the ImageBuffer, since our
     // ImageBuffer initializer won't fail.
     return scratch->context();
 }
 
 }  // namespace WebCore