C API: add sk_xfermode.h, impl, test

src/c/sk_paint.cpp

Index: src/c/sk_paint.cpp
diff --git a/src/c/sk_paint.cpp b/src/c/sk_paint.cpp
index e71285d4d5ca16924051fedc5750d28d558fc1be..330c796d7e21e4662700ddcdfa8a9c24c7542470 100644
--- a/src/c/sk_paint.cpp
+++ b/src/c/sk_paint.cpp
@@ -132,4 +132,43 @@ void sk_paint_set_stroke_join(sk_paint_t* cpaint, sk_stroke_join_t cjoin) {
     }
 }
 
-
+void sk_paint_set_xfermode_mode(sk_paint_t* paint, sk_xfermode_mode_t mode) {
+    SkASSERT(paint);
+    SkXfermode::Mode skmode;
+    switch (mode) {
+        #define MAP(X, Y) case (X): skmode = (Y); break
+        MAP( CLEAR_SK_XFERMODE_MODE,      SkXfermode::kClear_Mode      );
+        MAP( SRC_SK_XFERMODE_MODE,        SkXfermode::kSrc_Mode        );
+        MAP( DST_SK_XFERMODE_MODE,        SkXfermode::kDst_Mode        );
+        MAP( SRCOVER_SK_XFERMODE_MODE,    SkXfermode::kSrcOver_Mode    );
+        MAP( DSTOVER_SK_XFERMODE_MODE,    SkXfermode::kDstOver_Mode    );
+        MAP( SRCIN_SK_XFERMODE_MODE,      SkXfermode::kSrcIn_Mode      );
+        MAP( DSTIN_SK_XFERMODE_MODE,      SkXfermode::kDstIn_Mode      );
+        MAP( SRCOUT_SK_XFERMODE_MODE,     SkXfermode::kSrcOut_Mode     );
+        MAP( DSTOUT_SK_XFERMODE_MODE,     SkXfermode::kDstOut_Mode     );
+        MAP( SRCATOP_SK_XFERMODE_MODE,    SkXfermode::kSrcATop_Mode    );
+        MAP( DSTATOP_SK_XFERMODE_MODE,    SkXfermode::kDstATop_Mode    );
+        MAP( XOR_SK_XFERMODE_MODE,        SkXfermode::kXor_Mode        );
+        MAP( PLUS_SK_XFERMODE_MODE,       SkXfermode::kPlus_Mode       );
+        MAP( MODULATE_SK_XFERMODE_MODE,   SkXfermode::kModulate_Mode   );
+        MAP( SCREEN_SK_XFERMODE_MODE,     SkXfermode::kScreen_Mode     );
+        MAP( OVERLAY_SK_XFERMODE_MODE,    SkXfermode::kOverlay_Mode    );
+        MAP( DARKEN_SK_XFERMODE_MODE,     SkXfermode::kDarken_Mode     );
+        MAP( LIGHTEN_SK_XFERMODE_MODE,    SkXfermode::kLighten_Mode    );
+        MAP( COLORDODGE_SK_XFERMODE_MODE, SkXfermode::kColorDodge_Mode );
+        MAP( COLORBURN_SK_XFERMODE_MODE,  SkXfermode::kColorBurn_Mode  );
+        MAP( HARDLIGHT_SK_XFERMODE_MODE,  SkXfermode::kHardLight_Mode  );
+        MAP( SOFTLIGHT_SK_XFERMODE_MODE,  SkXfermode::kSoftLight_Mode  );
+        MAP( DIFFERENCE_SK_XFERMODE_MODE, SkXfermode::kDifference_Mode );
+        MAP( EXCLUSION_SK_XFERMODE_MODE,  SkXfermode::kExclusion_Mode  );
+        MAP( MULTIPLY_SK_XFERMODE_MODE,   SkXfermode::kMultiply_Mode   );
+        MAP( HUE_SK_XFERMODE_MODE,        SkXfermode::kHue_Mode        );
+        MAP( SATURATION_SK_XFERMODE_MODE, SkXfermode::kSaturation_Mode );
+        MAP( COLOR_SK_XFERMODE_MODE,      SkXfermode::kColor_Mode      );
+        MAP( LUMINOSITY_SK_XFERMODE_MODE, SkXfermode::kLuminosity_Mode );
+        #undef MAP
+        default:
+            return;
+    }
+    AsPaint(paint)->setXfermodeMode(skmode);
+}