Add special case circle blur for Ganesh

src/effects/GrCircleBlurFragmentProcessor.h

+/*
+ * 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 GrCircleBlurFragmentProcessor_DEFINED
+#define GrCircleBlurFragmentProcessor_DEFINED
+
+#include "SkTypes.h"
+
+#if SK_SUPPORT_GPU
+
+#include "GrFragmentProcessor.h"
+#include "GrProcessorUnitTest.h"
+
+class GrTextureProvider;
+
+// This FP handles the special case of a blurred circle. It uses a 1D 
+// profile that is just rotated about the origin of the circle.
+class GrCircleBlurFragmentProcessor : public GrFragmentProcessor {
+public:
+    ~GrCircleBlurFragmentProcessor() override {};
+
+    const char* name() const override { return "CircleBlur"; }
+
+    static const GrFragmentProcessor* Create(GrTextureProvider*textureProvider,
+                                             const SkRect& circle, float sigma) {
+        float offset;
+
+        SkAutoTUnref<GrTexture> blurProfile(CreateCircleBlurProfileTexture(textureProvider,
+                                                                           circle,
+                                                                           sigma,
+                                                                           &offset));
+        if (!blurProfile) {
+           return nullptr;
+        }
+        return new GrCircleBlurFragmentProcessor(circle, sigma, offset, blurProfile);
+    }
+
+    const SkRect& circle() const { return fCircle; }
+    float sigma() const { return fSigma; }
+    float offset() const { return fOffset; }
+    int profileSize() const { return fBlurProfileAccess.getTexture()->width(); }
+
+private:
+    GrCircleBlurFragmentProcessor(const SkRect& circle, float sigma,
+                                  float offset, GrTexture* blurProfile);
+
+    GrGLFragmentProcessor* onCreateGLInstance() const override;
+
+    void onGetGLProcessorKey(const GrGLSLCaps& caps, GrProcessorKeyBuilder* b) const override;
+
+    bool onIsEqual(const GrFragmentProcessor& other) const override {
+        const GrCircleBlurFragmentProcessor& cbfp = other.cast<GrCircleBlurFragmentProcessor>();
+        // fOffset is computed from the circle width and the sigma
+        return this->circle().width() == cbfp.circle().width() && fSigma == cbfp.fSigma;    
+    }
+
+    void onComputeInvariantOutput(GrInvariantOutput* inout) const override;
+
+    static GrTexture* CreateCircleBlurProfileTexture(GrTextureProvider*,
+                                                     const SkRect& circle,
+                                                     float sigma, float* offset);
+
+    SkRect              fCircle;
+    float               fSigma;
+    float               fOffset;
+    GrTextureAccess     fBlurProfileAccess;
+
+    GR_DECLARE_FRAGMENT_PROCESSOR_TEST;
+
+    typedef GrFragmentProcessor INHERITED;
+};
+
+#endif
+#endif