Added GrGLBlend.h|cpp with helper function AppendPorterDuffBlend() in preparation for SkComposeShader gpu backend

BUG=skia:

Review URL: https://codereview.chromium.org/1254833003

3 files changed, 95 insertions, 56 deletions

diff --git a/src/gpu/effects/GrPorterDuffXferProcessor.cpp b/src/gpu/effects/GrPorterDuffXferProcessor.cpp
index b6b57aefea..0e1bc51469 100644
--- a/src/gpu/effects/GrPorterDuffXferProcessor.cpp
+++ b/src/gpu/effects/GrPorterDuffXferProcessor.cpp
@@ -13,6 +13,7 @@
 #include "GrProcOptInfo.h"
 #include "GrTypes.h"
 #include "GrXferProcessor.h"
+#include "gl/GrGLBlend.h"
 #include "gl/GrGLXferProcessor.h"
 #include "gl/builders/GrGLFragmentShaderBuilder.h"
 #include "gl/builders/GrGLProgramBuilder.h"
@@ -488,50 +489,6 @@ private:
 
 ///////////////////////////////////////////////////////////////////////////////
 
-static bool append_porterduff_term(GrGLXPFragmentBuilder* fsBuilder, SkXfermode::Coeff coeff,
-                                   const char* colorName, const char* srcColorName,
-                                   const char* dstColorName, bool hasPrevious) {
-    if (SkXfermode::kZero_Coeff == coeff) {
-        return hasPrevious;
-    } else {
-        if (hasPrevious) {
-            fsBuilder->codeAppend(" + ");
-        }
-        fsBuilder->codeAppendf("%s", colorName);
-        switch (coeff) {
-            case SkXfermode::kOne_Coeff:
-                break;
-            case SkXfermode::kSC_Coeff:
-                fsBuilder->codeAppendf(" * %s", srcColorName);
-                break;
-            case SkXfermode::kISC_Coeff:
-                fsBuilder->codeAppendf(" * (vec4(1.0) - %s)", srcColorName);
-                break;
-            case SkXfermode::kDC_Coeff:
-                fsBuilder->codeAppendf(" * %s", dstColorName);
-                break;
-            case SkXfermode::kIDC_Coeff:
-                fsBuilder->codeAppendf(" * (vec4(1.0) - %s)", dstColorName);
-                break;
-            case SkXfermode::kSA_Coeff:
-                fsBuilder->codeAppendf(" * %s.a", srcColorName);
-                break;
-            case SkXfermode::kISA_Coeff:
-                fsBuilder->codeAppendf(" * (1.0 - %s.a)", srcColorName);
-                break;
-            case SkXfermode::kDA_Coeff:
-                fsBuilder->codeAppendf(" * %s.a", dstColorName);
-                break;
-            case SkXfermode::kIDA_Coeff:
-                fsBuilder->codeAppendf(" * (1.0 - %s.a)", dstColorName);
-                break;
-            default:
-                SkFAIL("Unsupported Blend Coeff");
-        }
-        return true;
-    }
-}
-
 class GLShaderPDXferProcessor : public GrGLXferProcessor {
 public:
     static void GenKey(const GrProcessor& processor, GrProcessorKeyBuilder* b) {
@@ -545,17 +502,7 @@ private:
         const ShaderPDXferProcessor& xp = proc.cast<ShaderPDXferProcessor>();
         GrGLXPFragmentBuilder* fsBuilder = pb->getFragmentShaderBuilder();
 
-        SkXfermode::Coeff srcCoeff, dstCoeff;
-        SkXfermode::ModeAsCoeff(xp.getXfermode(), &srcCoeff, &dstCoeff);
-
-        fsBuilder->codeAppendf("%s =", outColor);
-        // append src blend
-        bool didAppend = append_porterduff_term(fsBuilder, srcCoeff, srcColor, srcColor, dstColor,
-                                                false);
-        // append dst blend
-        SkAssertResult(append_porterduff_term(fsBuilder, dstCoeff, dstColor, srcColor, dstColor,
-                                              didAppend));
-        fsBuilder->codeAppend(";");
+        GrGLBlend::AppendPorterDuffBlend(fsBuilder, srcColor, dstColor, outColor, xp.getXfermode());
     }
 
     void onSetData(const GrGLProgramDataManager&, const GrXferProcessor&) override {}
@@ -824,4 +771,3 @@ void GrPorterDuffXPFactory::TestGetXPOutputTypes(const GrXferProcessor* xp,
     *outPrimary = blendFormula.fPrimaryOutputType;
     *outSecondary = blendFormula.fSecondaryOutputType;
 }
-
diff --git a/src/gpu/gl/GrGLBlend.cpp b/src/gpu/gl/GrGLBlend.cpp
new file mode 100644
index 0000000000..0f73fbdbdb
--- /dev/null
+++ b/src/gpu/gl/GrGLBlend.cpp
@@ -0,0 +1,69 @@
+/*
+ * 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 "GrGLBlend.h"
+#include "gl/builders/GrGLFragmentShaderBuilder.h"
+
+static bool append_porterduff_term(GrGLFragmentBuilder* fsBuilder, SkXfermode::Coeff coeff,
+                                   const char* colorName, const char* srcColorName,
+                                   const char* dstColorName, bool hasPrevious) {
+    if (SkXfermode::kZero_Coeff == coeff) {
+        return hasPrevious;
+    } else {
+        if (hasPrevious) {
+            fsBuilder->codeAppend(" + ");
+        }
+        fsBuilder->codeAppendf("%s", colorName);
+        switch (coeff) {
+            case SkXfermode::kOne_Coeff:
+                break;
+            case SkXfermode::kSC_Coeff:
+                fsBuilder->codeAppendf(" * %s", srcColorName);
+                break;
+            case SkXfermode::kISC_Coeff:
+                fsBuilder->codeAppendf(" * (vec4(1.0) - %s)", srcColorName);
+                break;
+            case SkXfermode::kDC_Coeff:
+                fsBuilder->codeAppendf(" * %s", dstColorName);
+                break;
+            case SkXfermode::kIDC_Coeff:
+                fsBuilder->codeAppendf(" * (vec4(1.0) - %s)", dstColorName);
+                break;
+            case SkXfermode::kSA_Coeff:
+                fsBuilder->codeAppendf(" * %s.a", srcColorName);
+                break;
+            case SkXfermode::kISA_Coeff:
+                fsBuilder->codeAppendf(" * (1.0 - %s.a)", srcColorName);
+                break;
+            case SkXfermode::kDA_Coeff:
+                fsBuilder->codeAppendf(" * %s.a", dstColorName);
+                break;
+            case SkXfermode::kIDA_Coeff:
+                fsBuilder->codeAppendf(" * (1.0 - %s.a)", dstColorName);
+                break;
+            default:
+                SkFAIL("Unsupported Blend Coeff");
+        }
+        return true;
+    }
+}
+
+void GrGLBlend::AppendPorterDuffBlend(GrGLFragmentBuilder* fsBuilder, const char* srcColor,
+                                      const char* dstColor, const char* outColor,
+                                      SkXfermode::Mode mode) {
+
+    SkXfermode::Coeff srcCoeff, dstCoeff;
+    SkXfermode::ModeAsCoeff(mode, &srcCoeff, &dstCoeff);
+
+    fsBuilder->codeAppendf("%s =", outColor);
+    // append src blend
+    bool didAppend = append_porterduff_term(fsBuilder, srcCoeff, srcColor, srcColor, dstColor,
+                                            false);
+    // append dst blend
+    SkAssertResult(append_porterduff_term(fsBuilder, dstCoeff, dstColor, srcColor, dstColor,
+                                          didAppend));
+    fsBuilder->codeAppend(";");
+}
diff --git a/src/gpu/gl/GrGLBlend.h b/src/gpu/gl/GrGLBlend.h
new file mode 100644
index 0000000000..af447b47bf
--- /dev/null
+++ b/src/gpu/gl/GrGLBlend.h
@@ -0,0 +1,24 @@
+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrGLBlend_DEFINED
+#define GrGLBlend_DEFINED
+
+#include "SkXfermode.h"
+
+class GrGLFragmentBuilder;
+
+namespace GrGLBlend {
+    /*
+     * Appends GLSL code to fsBuilder that assigns a specified blend of the srcColor and dstColor
+     * variables to the outColor variable.
+     */
+    void AppendPorterDuffBlend(GrGLFragmentBuilder* fsBuilder, const char* srcColor,
+                               const char* dstColor, const char* outColor, SkXfermode::Mode mode);
+};
+
+#endif