Create xfer processor backend.

src/gpu/gl/GrGLXferProcessor.h

+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrGLXferProcessor_DEFINED
+#define GrGLXferProcessor_DEFINED
+
+#include "GrGLProcessor.h"
+
+class GrGLXPBuilder;
+
+class GrGLXferProcessor {
+public:
+    GrGLXferProcessor() {}
+    virtual ~GrGLXferProcessor() {}
+
+    typedef GrGLProcessor::TextureSamplerArray TextureSamplerArray;
+    struct EmitArgs {
+        EmitArgs(GrGLXPBuilder* pb,
+                 const GrXferProcessor& xp,
+                 const char* inputColor,
+                 const char* inputCoverage,
+                 const char* outputPrimary,
+                 const char* outputSecondary,
+                 const TextureSamplerArray& samplers)
+            : fPB(pb)
+            , fXP(xp)
+            , fInputColor(inputColor)
+            , fInputCoverage(inputCoverage)
+            , fOutputPrimary(outputPrimary)
+            , fOutputSecondary(outputSecondary)
+            , fSamplers(samplers) {}
+
+        GrGLXPBuilder* fPB;
+        const GrXferProcessor& fXP;
+        const char* fInputColor;
+        const char* fInputCoverage;
+        const char* fOutputPrimary;
+        const char* fOutputSecondary;
+        const TextureSamplerArray& fSamplers;
+    };
+    /**

[bsalomon, 2014/12/08 19:58:59]

Comment seems like it was lifted from somewhere and doesn't apply here

+     * This is similar to emitCode() in the base class, except it takes a full shader builder.
+     * This allows the effect subclass to emit vertex code.
+     */
+    virtual void emitCode(const EmitArgs&) = 0;
+
+    /** A GrGLXferProcessor instance can be reused with any GrGLXferProcessor that produces
+        the same stage key; this function reads data from a GrGLXferProcessor and uploads any
+        uniform variables required  by the shaders created in emitCode(). The GrXferProcessor
+        parameter is guaranteed to be of the same type that created this GrGLXferProcessor and
+        to have an identical processor key as the one that created this GrGLXferProcessor.  */
+    virtual void setData(const GrGLProgramDataManager&,
+                         const GrXferProcessor&) = 0;
+private:
+    typedef GrGLProcessor INHERITED;
+};
+#endif