Add canvas blending modes under a runtime flag

Source/WebCore/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 42 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)
+static const struct BlendOpToXfermodeMode {
+    uint8_t mBlendOp;
+    uint8_t m_xfermodeMode;
+} gMapBlendOpsToXfermodeModes[] = {
+    { BlendModeMultiply,        SkXfermode::kMultiply_Mode },
+    { BlendModeScreen,          SkXfermode::kScreen_Mode },
+    { BlendModeOverlay,         SkXfermode::kOverlay_Mode },
+    { BlendModeDarken,          SkXfermode::kDarken_Mode },
+    { BlendModeLighten,         SkXfermode::kLighten_Mode },
+    { BlendModeColorDodge,      SkXfermode::kColorDodge_Mode },
+    { BlendModeColorBurn,       SkXfermode::kColorBurn_Mode },
+    { BlendModeHardLight,       SkXfermode::kHardLight_Mode },
+    { BlendModeSoftLight,       SkXfermode::kSoftLight_Mode },
+    { BlendModeDifference,      SkXfermode::kDifference_Mode },
+    { BlendModeExclusion,       SkXfermode::kExclusion_Mode },
+    { BlendModeHue,             SkXfermode::kHue_Mode },
+    { BlendModeSaturation,      SkXfermode::kSaturation_Mode },
+    { BlendModeColor,           SkXfermode::kColor_Mode },
+    { BlendModeLuminosity,      SkXfermode::kLuminosity_Mode }
+};

[Stephen Chennney, 2013/04/08 16:07:02]

This should be implemented as an array. If the BlendModeMultiply is not
zero-based, you can always index the array by (blendMode - BlendModeMultiply).
You are only ever converting in one direction, so the loop is not needed.

[rosca, 2013/04/08 19:53:25]

I followed the example of CompositOpToXfermodeMode. I changed it to an array
with the last upload. Should I change the CompositeOpToXfermodeMode also with
this review?

+
+SkXfermode::Mode WebCoreCompositeToSkiaComposite(CompositeOperator op, BlendMode blendMode)
 {
+    if (blendMode != BlendModeNormal) {

[Stephen Chennney, 2013/04/08 16:07:02]

Is BlendModeNormal == 0? If so, suitably adjust my statements above.

+        const BlendOpToXfermodeMode* table = gMapBlendOpsToXfermodeModes;
+        for (unsigned i = 0; i < SK_ARRAY_COUNT(gMapBlendOpsToXfermodeModes); i++) {
+            if (table[i].mBlendOp == blendMode)
+                return (SkXfermode::Mode)table[i].m_xfermodeMode;
+        }
+    }
+
     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