Add canvas blending modes under a runtime flag

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

Index: Source/WebCore/platform/graphics/skia/SkiaUtils.cpp
===================================================================
--- Source/WebCore/platform/graphics/skia/SkiaUtils.cpp	(revision 147814)
+++ Source/WebCore/platform/graphics/skia/SkiaUtils.cpp	(working copy)
@@ -60,8 +60,37 @@
     { 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++) {