Update SampleAndroidShadows to use algorithm closer to Android OpenGL

src/effects/SkGaussianEdgeShader.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkGaussianEdgeShader.h"
 #include "SkReadBuffer.h"
 #include "SkWriteBuffer.h"
 
  /** \class SkGaussianEdgeShaderImpl
  This subclass of shader applies a Gaussian to shadow edge
 
+ If largerBlur is false:
  The radius of the Gaussian blur is specified by the g value of the color, in 6.2 fixed point.
  For spot shadows, we increase the stroke width to set the shadow against the shape. This pad
  is specified by b, also in 6.2 fixed point. The r value represents the max final alpha.
  The incoming alpha should be 1.
+
+ If largerBlur is true:
+ The radius of the Gaussian blur is specified by the r & g values of the color in 14.2 fixed point.
+ For spot shadows, we increase the stroke width to set the shadow against the shape. This pad
+ is specified by b, also in 6.2 fixed point. The a value represents the max final alpha.
+

[herb_g, 2016/09/09 21:06:47]

Add a TODO about removing largerBlur when the dep from Android is gone.

  */
 class SkGaussianEdgeShaderImpl : public SkShader {
 public:
-    SkGaussianEdgeShaderImpl() {}
+    SkGaussianEdgeShaderImpl()
+        : fLargerBlur(false) {}
+
+    SkGaussianEdgeShaderImpl(bool largerBlur)
+        : fLargerBlur(largerBlur) {}
 
     bool isOpaque() const override;
 
 #if SK_SUPPORT_GPU
     sk_sp<GrFragmentProcessor> asFragmentProcessor(const AsFPArgs&) const override;
 #endif
 
     SK_TO_STRING_OVERRIDE()
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkGaussianEdgeShaderImpl)
 
 protected:
     void flatten(SkWriteBuffer&) const override;
 
 private:
     friend class SkGaussianEdgeShader;
+    bool fLargerBlur;
 
     typedef SkShader INHERITED;
 };
 
 ////////////////////////////////////////////////////////////////////////////
 
 #if SK_SUPPORT_GPU
 
 #include "GrCoordTransform.h"
 #include "GrFragmentProcessor.h"
 #include "GrInvariantOutput.h"
 #include "glsl/GrGLSLFragmentProcessor.h"
 #include "glsl/GrGLSLFragmentShaderBuilder.h"
 #include "glsl/GrGLSLProgramDataManager.h"
 #include "glsl/GrGLSLUniformHandler.h"
 #include "SkGr.h"
 #include "SkGrPriv.h"
 
 class GaussianEdgeFP : public GrFragmentProcessor {
 public:
-    GaussianEdgeFP() {
+    GaussianEdgeFP(bool largerBlur) : fLargerBlur(largerBlur) {
         this->initClassID<GaussianEdgeFP>();
 
         // enable output of distance information for shape
         fUsesDistanceVectorField = true;
     }
 
     class GLSLGaussianEdgeFP : public GrGLSLFragmentProcessor {
     public:
-        GLSLGaussianEdgeFP() {}
+        GLSLGaussianEdgeFP(bool largerBlur) : fLargerBlur(largerBlur) {}
 
         void emitCode(EmitArgs& args) override {
             GrGLSLFPFragmentBuilder* fragBuilder = args.fFragBuilder;
 
             if (!args.fGpImplementsDistanceVector) {
                 fragBuilder->codeAppendf("// GP does not implement fsDistanceVector - "
                                          " returning grey in GLSLGaussianEdgeFP\n");
                 fragBuilder->codeAppendf("vec4 color = %s;", args.fInputColor);
                 fragBuilder->codeAppendf("%s = vec4(0, 0, 0, color.r);", args.fOutputColor);
+            } else if (fLargerBlur) {
+                fragBuilder->codeAppendf("vec4 color = %s;", args.fInputColor);
+                fragBuilder->codeAppend("float radius = color.r*256*64 + color.g*64;");
+                fragBuilder->codeAppend("float pad = color.b*64;");
+
+                fragBuilder->codeAppendf("float factor = 1 - clamp((%s.z - pad)/radius, 0, 1);",
+                                         fragBuilder->distanceVectorName());
+                fragBuilder->codeAppend("factor = exp(-factor * factor * 4) - 0.018;");
+                fragBuilder->codeAppendf("%s = factor*vec4(0, 0, 0, color.a);",
+                                         args.fOutputColor);
             } else {
                 fragBuilder->codeAppendf("vec4 color = %s;", args.fInputColor);
-                fragBuilder->codeAppend("float radius = color.g*64.0;");
-                fragBuilder->codeAppend("float pad = color.b*64.0;");
+                fragBuilder->codeAppend("float radius = color.g*64;");
+                fragBuilder->codeAppend("float pad = color.b*64;");
 
-                fragBuilder->codeAppendf("float factor = 1.0 - clamp((%s.z - pad)/radius,"
-                                                                    "0.0, 1.0);",
+                fragBuilder->codeAppendf("float factor = 1 - clamp((%s.z - pad)/radius, 0, 1);",
                                          fragBuilder->distanceVectorName());
-                fragBuilder->codeAppend("factor = exp(-factor * factor * 4.0) - 0.018;");
-                fragBuilder->codeAppendf("%s = factor*vec4(0.0, 0.0, 0.0, color.r);",
+                fragBuilder->codeAppend("factor = exp(-factor * factor * 4) - 0.018;");
+                fragBuilder->codeAppendf("%s = factor*vec4(0, 0, 0, color.r);",
                                          args.fOutputColor);
             }
         }
 
         static void GenKey(const GrProcessor& proc, const GrGLSLCaps&,
                            GrProcessorKeyBuilder* b) {
-            // only one shader generated currently
-            b->add32(0x0);
+            const GaussianEdgeFP& gefp = proc.cast<GaussianEdgeFP>();
+            b->add32(gefp.fLargerBlur ? 0x1 : 0x0);
         }
 
     protected:
         void onSetData(const GrGLSLProgramDataManager& pdman, const GrProcessor& proc) override {}
+
+        bool fLargerBlur;
     };
 
     void onGetGLSLProcessorKey(const GrGLSLCaps& caps, GrProcessorKeyBuilder* b) const override {
         GLSLGaussianEdgeFP::GenKey(*this, caps, b);
     }
 
     const char* name() const override { return "GaussianEdgeFP"; }
 
     void onComputeInvariantOutput(GrInvariantOutput* inout) const override {
         inout->mulByUnknownFourComponents();
     }
 
 private:
-    GrGLSLFragmentProcessor* onCreateGLSLInstance() const override { return new GLSLGaussianEdgeFP; }
+    GrGLSLFragmentProcessor* onCreateGLSLInstance() const override {
+        return new GLSLGaussianEdgeFP(fLargerBlur);
+    }
 
     bool onIsEqual(const GrFragmentProcessor& proc) const override { return true; }
+
+    bool fLargerBlur;
 };
 
 ////////////////////////////////////////////////////////////////////////////
 
 sk_sp<GrFragmentProcessor> SkGaussianEdgeShaderImpl::asFragmentProcessor(const AsFPArgs& args) const {
-    return sk_make_sp<GaussianEdgeFP>();
+    return sk_make_sp<GaussianEdgeFP>(fLargerBlur);
 }
 
 #endif
 
 ////////////////////////////////////////////////////////////////////////////
 
 bool SkGaussianEdgeShaderImpl::isOpaque() const {
     return false;
 }
 
 ////////////////////////////////////////////////////////////////////////////
 
 #ifndef SK_IGNORE_TO_STRING
 void SkGaussianEdgeShaderImpl::toString(SkString* str) const {
     str->appendf("GaussianEdgeShader: ()");
 }
 #endif
 
 sk_sp<SkFlattenable> SkGaussianEdgeShaderImpl::CreateProc(SkReadBuffer& buf) {
     return sk_make_sp<SkGaussianEdgeShaderImpl>();
 }
 
 void SkGaussianEdgeShaderImpl::flatten(SkWriteBuffer& buf) const {
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 
-sk_sp<SkShader> SkGaussianEdgeShader::Make() {
-    return sk_make_sp<SkGaussianEdgeShaderImpl>();
+sk_sp<SkShader> SkGaussianEdgeShader::Make(bool largerBlur) {
+    return sk_make_sp<SkGaussianEdgeShaderImpl>(largerBlur);
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 
 SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_START(SkGaussianEdgeShader)
 SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(SkGaussianEdgeShaderImpl)
 SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_END
 
 ///////////////////////////////////////////////////////////////////////////////