Apply coverage in XP base class when using dst reads

src/effects/SkArithmeticMode_gpu.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkArithmeticMode_gpu.h"
 
 #if SK_SUPPORT_GPU
@@ skipping 154 matching lines @@
         return SkNEW_ARGS(ArithmeticXP, (k1, k2, k3, k4, enforcePMColor, dstTexture,
                                          willReadDstColor));
     }
 
     ~ArithmeticXP() override {};
 
     const char* name() const override { return "Arithmetic"; }
 
     GrGLXferProcessor* createGLInstance() const override;
 
-    bool hasSecondaryOutput() const override { return false; }
-
     float k1() const { return fK1; }
     float k2() const { return fK2; }
     float k3() const { return fK3; }
     float k4() const { return fK4; }
     bool enforcePMColor() const { return fEnforcePMColor; }
 
 private:
     ArithmeticXP(float k1, float k2, float k3, float k4, bool enforcePMColor,
                    const DstTexture*, bool willReadDstColor);
 
@@ skipping 34 matching lines @@
     ~GLArithmeticXP() override {}
 
     static void GenKey(const GrProcessor& processor, const GrGLSLCaps& caps,
                        GrProcessorKeyBuilder* b) {
         const ArithmeticXP& arith = processor.cast<ArithmeticXP>();
         uint32_t key = arith.enforcePMColor() ? 1 : 0;
         b->add32(key);
     }
 
 private:
-    void onEmitCode(const EmitArgs& args) override {
-        GrGLXPFragmentBuilder* fsBuilder = args.fPB->getFragmentShaderBuilder();
+    void emitBlendCodeForDstRead(GrGLXPBuilder* pb, const char* srcColor, const char* dstColor,
+                                 const char* outColor, const GrXferProcessor& proc) override {
+        GrGLXPFragmentBuilder* fsBuilder = pb->getFragmentShaderBuilder();
 
-        const char* dstColor = fsBuilder->dstColor();
+        fKUni = pb->addUniform(GrGLProgramBuilder::kFragment_Visibility,
+                               kVec4f_GrSLType, kDefault_GrSLPrecision,
+                               "k");
+        const char* kUni = pb->getUniformCStr(fKUni);
 
-        fKUni = args.fPB->addUniform(GrGLProgramBuilder::kFragment_Visibility,
-                                     kVec4f_GrSLType, kDefault_GrSLPrecision,
-                                     "k");
-        const char* kUni = args.fPB->getUniformCStr(fKUni);
-
-        add_arithmetic_code(fsBuilder, args.fInputColor, dstColor, args.fOutputPrimary, kUni, 
-                            fEnforcePMColor);
-
-        fsBuilder->codeAppendf("%s = %s * %s + (vec4(1.0) - %s) * %s;",
-                               args.fOutputPrimary, args.fOutputPrimary, args.fInputCoverage,
-                               args.fInputCoverage, dstColor);
+        add_arithmetic_code(fsBuilder, srcColor, dstColor, outColor, kUni, fEnforcePMColor);
     }
 
     void onSetData(const GrGLProgramDataManager& pdman,
                    const GrXferProcessor& processor) override {
         const ArithmeticXP& arith = processor.cast<ArithmeticXP>();
         pdman.set4f(fKUni, arith.k1(), arith.k2(), arith.k3(), arith.k4());
         fEnforcePMColor = arith.enforcePMColor();
     };
 
     GrGLProgramDataManager::UniformHandle fKUni;
@@ skipping 68 matching lines @@
     float k1 = random->nextF();
     float k2 = random->nextF();
     float k3 = random->nextF();
     float k4 = random->nextF();
     bool enforcePMColor = random->nextBool();
 
     return GrArithmeticXPFactory::Create(k1, k2, k3, k4, enforcePMColor);
 }
 
 #endif