Add special case circle blur for Ganesh

src/effects/GrCircleBlurFragmentProcessor.cpp

Index: src/effects/GrCircleBlurFragmentProcessor.cpp
diff --git a/src/effects/GrCircleBlurFragmentProcessor.cpp b/src/effects/GrCircleBlurFragmentProcessor.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..c5aafdce0eb94e263b349841d6b7454cec38b7e2
--- /dev/null
+++ b/src/effects/GrCircleBlurFragmentProcessor.cpp
@@ -0,0 +1,259 @@
+
+/*
+ * 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 "GrCircleBlurFragmentProcessor.h"
+
+#if SK_SUPPORT_GPU
+
+#include "GrContext.h"
+#include "GrTextureProvider.h"
+
+#include "gl/GrGLFragmentProcessor.h"
+#include "gl/builders/GrGLProgramBuilder.h"
+
+class GrGLCircleBlurFragmentProcessor : public GrGLFragmentProcessor {
+public:
+    GrGLCircleBlurFragmentProcessor(const GrProcessor&) {}
+    void emitCode(EmitArgs&) override;
+
+protected:
+    void onSetData(const GrGLProgramDataManager&, const GrProcessor&) override;
+
+private:
+    GrGLProgramDataManager::UniformHandle fDataUniform;
+
+    typedef GrGLFragmentProcessor INHERITED;
+};
+
+void GrGLCircleBlurFragmentProcessor::emitCode(EmitArgs& args) {
+
+    const char *dataName;
+
+    // The data is formatted as:
+    // x,y  - the center of the circle
+    // z    - the distance at which the intensity starts falling off (e.g., the start of the table)
+    // w    - the size of the profile texture
+    fDataUniform = args.fBuilder->addUniform(GrGLProgramBuilder::kFragment_Visibility,
+                                             kVec4f_GrSLType,
+                                             kDefault_GrSLPrecision,
+                                             "data",
+                                             &dataName);
+
+    GrGLFragmentBuilder* fsBuilder = args.fBuilder->getFragmentShaderBuilder();
+    const char *fragmentPos = fsBuilder->fragmentPosition();
+
+    if (args.fInputColor) {
+        fsBuilder->codeAppendf("vec4 src=%s;", args.fInputColor);
+    } else {
+        fsBuilder->codeAppendf("vec4 src=vec4(1);");
+    }
+
+    fsBuilder->codeAppendf("vec2 vec = %s.xy - %s.xy;", fragmentPos, dataName);
+    fsBuilder->codeAppendf("float dist = (length(vec) - %s.z + 0.5) / %s.w;", dataName, dataName);
+
+    fsBuilder->codeAppendf("float intensity = ");
+    fsBuilder->appendTextureLookup(args.fSamplers[0], "vec2(dist, 0.5)");
+    fsBuilder->codeAppend(".a;");
+
+    fsBuilder->codeAppendf("%s = src * intensity;\n", args.fOutputColor );
+}
+
+void GrGLCircleBlurFragmentProcessor::onSetData(const GrGLProgramDataManager& pdman,
+                                                const GrProcessor& proc) {
+    const GrCircleBlurFragmentProcessor& cbfp = proc.cast<GrCircleBlurFragmentProcessor>();
+    const SkRect& circle = cbfp.circle();
+
+    // The data is formatted as:
+    // x,y  - the center of the circle
+    // z    - the distance at which the intensity starts falling off (e.g., the start of the table)
+    // w    - the size of the profile texture
+    pdman.set4f(fDataUniform, circle.centerX(), circle.centerY(), cbfp.offset(),
+                SkIntToScalar(cbfp.profileSize()));
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+GrCircleBlurFragmentProcessor::GrCircleBlurFragmentProcessor(const SkRect& circle,
+                                                             float sigma,
+                                                             float offset,
+                                                             GrTexture* blurProfile) 
+    : fCircle(circle)
+    , fSigma(sigma)
+    , fOffset(offset)
+    , fBlurProfileAccess(blurProfile, GrTextureParams::kBilerp_FilterMode) {
+    this->initClassID<GrCircleBlurFragmentProcessor>();
+    this->addTextureAccess(&fBlurProfileAccess);
+    this->setWillReadFragmentPosition();
+}
+
+GrGLFragmentProcessor* GrCircleBlurFragmentProcessor::onCreateGLInstance() const {
+    return new GrGLCircleBlurFragmentProcessor(*this);
+}
+
+void GrCircleBlurFragmentProcessor::onGetGLProcessorKey(const GrGLSLCaps& caps,
+                                                        GrProcessorKeyBuilder* b) const {
+    GrGLCircleBlurFragmentProcessor::GenKey(*this, caps, b);
+}
+
+void GrCircleBlurFragmentProcessor::onComputeInvariantOutput(GrInvariantOutput* inout) const {
+    inout->mulByUnknownSingleComponent();
+}
+
+// Evaluate an AA circle function centered at the origin with 'radius' at (x,y)
+static inline float disk(float x, float y, float radius) {
+    float distSq = x*x + y*y;
+    if (distSq <= (radius-0.5f)*(radius-0.5f)) {
+        return 1.0f;
+    } else if (distSq >= (radius+0.5f)*(radius+0.5f)) {
+        return 0.0f;
+    } else {
+        float ramp = radius + 0.5f - sqrt(distSq);
+        SkASSERT(ramp >= 0.0f && ramp <= 1.0f);
+        return ramp;
+    }
+}
+
+// Create the top half of an even-sized Gaussian kernel
+static void make_half_kernel(float* kernel, int kernelWH, float sigma) {
+    SkASSERT(!(kernelWH & 1));
+
+    const float kernelOff = (kernelWH-1)/2.0f;
+
+    float b = 1.0f / (2.0f * sigma * sigma);
+    // omit the scale term since we're just going to renormalize
+
+    float tot = 0.0f;
+    for (int y = 0; y < kernelWH/2; ++y) {
+        for (int x = 0; x < kernelWH/2; ++x) {
+            // TODO: use a cheap approximation of the 2D Guassian?
+            float x2 = (x-kernelOff) * (x-kernelOff);
+            float y2 = (y-kernelOff) * (y-kernelOff);
+            // The kernel is symmetric so only compute it once for both sides
+            kernel[y*kernelWH+(kernelWH-x-1)] = kernel[y*kernelWH+x] = exp(-(x2 + y2) * b);
+            tot += 2.0f * kernel[y*kernelWH+x];
+        }
+    }
+    // Still normalize the half kernel to 1.0 (rather than 0.5) so we don't
+    // have to scale by 2.0 after convolution.
+    for (int y = 0; y < kernelWH/2; ++y) {
+        for (int x = 0; x < kernelWH; ++x) {
+            kernel[y*kernelWH+x] /= tot;
+        }
+    }
+}
+
+// Apply the half-kernel at 't' away from the center of the circle
+static uint8_t eval_at(float t, float halfWidth, float* halfKernel, int kernelWH) {
+    SkASSERT(!(kernelWH & 1));
+
+    const float kernelOff = (kernelWH-1)/2.0f;
+
+    float acc = 0;
+
+    for (int y = 0; y < kernelWH/2; ++y) {
+        if (kernelOff-y > halfWidth+0.5f) {
+            // All disk() samples in this row will be 0.0f
+            continue;
+        }
+
+        for (int x = 0; x < kernelWH; ++x) {
+            float image = disk(t - kernelOff + x, -kernelOff + y, halfWidth);
+            float kernel = halfKernel[y*kernelWH+x];
+            acc += kernel * image;
+        }
+    }
+
+    return SkUnitScalarClampToByte(acc);
+}
+
+static inline void compute_profile_offset_and_size(float halfWH, float sigma,
+                                                   float* offset, int* size) {
+
+    if (3*sigma <= halfWH) {
+        // The circle is bigger than the Gaussian. In this case we know the interior of the
+        // blurred circle is solid.
+        *offset = halfWH - 3 * sigma; // This location maps to 0.5f in the weights texture.
+                                     // It should always be 255.
+        *size = SkScalarCeilToInt(6*sigma);
+    } else {
+        // The Gaussian is bigger than the circle.
+        *offset = 0.0f;
+        *size = SkScalarCeilToInt(halfWH + 3*sigma);
+    }
+}
+
+static uint8_t* create_profile(float halfWH, float sigma) {
+
+    int kernelWH = SkScalarCeilToInt(6.0f*sigma);
+    kernelWH = (kernelWH + 1) & ~1; // make it the next even number up
+
+    SkAutoTArray<float> halfKernel(kernelWH*kernelWH/2);
+
+    make_half_kernel(halfKernel.get(), kernelWH, sigma);
+
+    float offset;
+    int numSteps;
+
+    compute_profile_offset_and_size(halfWH, sigma, &offset, &numSteps);
+
+    uint8_t* weights = new uint8_t[numSteps];
+    for (int i = 0; i < numSteps; ++i) {
+        weights[i] = eval_at(offset+i, halfWH, halfKernel.get(), kernelWH);
+    }
+
+    return weights;
+}
+
+GrTexture* GrCircleBlurFragmentProcessor::CreateCircleBlurProfileTexture(
+                                                                GrTextureProvider* textureProvider,
+                                                                const SkRect& circle,
+                                                                float sigma,
+                                                                float* offset) {
+    float halfWH = circle.width() / 2.0f;
+
+    int size;
+    compute_profile_offset_and_size(halfWH, sigma, offset, &size);
+
+    GrSurfaceDesc texDesc;
+    texDesc.fWidth = size;
+    texDesc.fHeight = 1;
+    texDesc.fConfig = kAlpha_8_GrPixelConfig;
+
+    static const GrUniqueKey::Domain kDomain = GrUniqueKey::GenerateDomain();
+    GrUniqueKey key;
+    GrUniqueKey::Builder builder(&key, kDomain, 2);
+    // The profile curve varies with both the sigma of the Gaussian and the size of the
+    // disk. Quantizing to 16.16 should be close enough though.
+    builder[0] = SkScalarToFixed(sigma);
+    builder[1] = SkScalarToFixed(halfWH);
+    builder.finish();
+
+    GrTexture *blurProfile = textureProvider->findAndRefTextureByUniqueKey(key);
+
+    if (!blurProfile) {
+        SkAutoTDeleteArray<uint8_t> profile(create_profile(halfWH, sigma));
+
+        blurProfile = textureProvider->createTexture(texDesc, true, profile.get(), 0);
+        if (blurProfile) {
+            textureProvider->assignUniqueKeyToTexture(key, blurProfile);
+        }
+    }
+
+    return blurProfile;
+}
+
+GR_DEFINE_FRAGMENT_PROCESSOR_TEST(GrCircleBlurFragmentProcessor);
+
+const GrFragmentProcessor* GrCircleBlurFragmentProcessor::TestCreate(GrProcessorTestData* d) {
+    SkScalar wh = d->fRandom->nextRangeScalar(100.f, 1000.f);
+    SkScalar sigma = d->fRandom->nextRangeF(1.f,10.f);
+    SkRect circle = SkRect::MakeWH(wh, wh);
+    return GrCircleBlurFragmentProcessor::Create(d->fContext->textureProvider(), circle, sigma);
+}
+
+#endif