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

src/core/SkXfermode.cpp

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkXfermode.h"
 #include "SkXfermode_proccoeff.h"
 #include "SkColorPriv.h"
@@ skipping 1454 matching lines @@
         case kSoftLight_Mode:  p->append(SkRasterPipeline::softlight);  return true;
 
         // TODO
         case kColor_Mode:       return false;
         case kHue_Mode:         return false;
         case kLuminosity_Mode:  return false;
         case kSaturation_Mode:  return false;
     }
     return false;
 }
+
+///////////////////////////////////////////////////////////////////////////////////////////////////
+
+bool SkBlendMode_SupportsCoverageAsAlpha(SkBlendMode mode) {
+    switch (mode) {
+        case SkBlendMode::kDst:
+        case SkBlendMode::kSrcOver:
+        case SkBlendMode::kDstOver:
+        case SkBlendMode::kDstOut:
+        case SkBlendMode::kSrcATop:
+        case SkBlendMode::kXor:
+        case SkBlendMode::kPlus:
+            return true;
+        default:
+            break;
+    }
+    return false;
+}
+
+bool SkXfermode::IsOpaque(SkBlendMode mode, SrcColorOpacity opacityType) {
+    const ProcCoeff rec = gProcCoeffs[(int)mode];
+
+    switch (rec.fSC) {
+        case kDA_Coeff:
+        case kDC_Coeff:
+        case kIDA_Coeff:
+        case kIDC_Coeff:
+            return false;
+        default:
+            break;
+    }
+
+    switch (rec.fDC) {
+        case kZero_Coeff:
+            return true;
+        case kISA_Coeff:
+            return kOpaque_SrcColorOpacity == opacityType;
+        case kSA_Coeff:
+            return kTransparentBlack_SrcColorOpacity == opacityType ||
+            kTransparentAlpha_SrcColorOpacity == opacityType;
+        case kSC_Coeff:
+            return kTransparentBlack_SrcColorOpacity == opacityType;
+        default:
+            return false;
+    }
+    return false;
+}
+
+#if SK_SUPPORT_GPU
+sk_sp<GrXPFactory> SkBlendMode_AsXPFactory(SkBlendMode mode) {
+    const ProcCoeff rec = gProcCoeffs[(int)mode];
+    if (CANNOT_USE_COEFF != rec.fSC) {
+        sk_sp<GrXPFactory> result(GrPorterDuffXPFactory::Make(mode));
+        SkASSERT(result);
+        return result;
+    }
+
+    SkASSERT(GrCustomXfermode::IsSupportedMode((SkXfermode::Mode)mode));
+    return GrCustomXfermode::MakeXPFactory((SkXfermode::Mode)mode);
+}
+#endif