Hook in rough distance field support for fonts

src/gpu/effects/GrDistanceFieldTextureEffect.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
-#include "GrCustomCoordsTextureEffect.h"
+#include "GrDistanceFieldTextureEffect.h"
 #include "gl/GrGLEffect.h"
 #include "gl/GrGLSL.h"
 #include "gl/GrGLTexture.h"
 #include "gl/GrGLVertexEffect.h"
 #include "GrTBackendEffectFactory.h"
 #include "GrTexture.h"
 
-class GrGLCustomCoordsTextureEffect : public GrGLVertexEffect {
+// The distance field is constructed as unsigned char values, so that the zero value is at 128.
+// Hence our zero threshold is 128/255. 
+#define THRESHOLD "0.50196078431"
+
+class GrGLDistanceFieldTextureEffect : public GrGLVertexEffect {
 public:
-    GrGLCustomCoordsTextureEffect(const GrBackendEffectFactory& factory, const GrDrawEffect& drawEffect)
+    GrGLDistanceFieldTextureEffect(const GrBackendEffectFactory& factory, const GrDrawEffect& drawEffect)
         : INHERITED (factory) {}
 
     virtual void emitCode(GrGLFullShaderBuilder* builder,
                           const GrDrawEffect& drawEffect,
                           EffectKey key,
                           const char* outputColor,
                           const char* inputColor,
                           const TransformedCoordsArray&,
                           const TextureSamplerArray& samplers) SK_OVERRIDE {
-        SkASSERT(1 == drawEffect.castEffect<GrCustomCoordsTextureEffect>().numVertexAttribs());
+        SkASSERT(1 == drawEffect.castEffect<GrDistanceFieldTextureEffect>().numVertexAttribs());
 
         SkString fsCoordName;
         const char* vsVaryingName;
         const char* fsVaryingNamePtr;
         builder->addVarying(kVec2f_GrSLType, "textureCoords", &vsVaryingName, &fsVaryingNamePtr);
         fsCoordName = fsVaryingNamePtr;
 
         const char* attrName =
             builder->getEffectAttributeName(drawEffect.getVertexAttribIndices()[0])->c_str();
         builder->vsCodeAppendf("\t%s = %s;\n", vsVaryingName, attrName);
 
-        builder->fsCodeAppendf("\t%s = ", outputColor);
-        builder->fsAppendTextureLookupAndModulate(inputColor,
-                                                  samplers[0],
-                                                  fsCoordName.c_str(),
-                                                  kVec2f_GrSLType);
+        builder->fsCodeAppend("\tvec4 texColor = ");
+        builder->fsAppendTextureLookup(samplers[0],
+                                       fsCoordName.c_str(),
+                                       kVec2f_GrSLType);
         builder->fsCodeAppend(";\n");
+        builder->fsCodeAppend("\tfloat distance = texColor.r;\n");
+        // this gives us a smooth step across approximately one fragment 
+        // (assuming a radius of the diagonal of the fragment, hence a factor of sqrt(2)/2)
+        builder->fsCodeAppend("\tfloat afwidth = 0.7071*length(vec2(dFdx(distance), dFdy(distance)));\n");
+        builder->fsCodeAppend("\tfloat val = smoothstep("THRESHOLD"-afwidth, "THRESHOLD"+afwidth, distance);\n");
+
+        builder->fsCodeAppendf("\t%s = %s;\n", outputColor,
+                                   (GrGLSLExpr4(inputColor) * GrGLSLExpr1("val")).c_str());
     }
 
     virtual void setData(const GrGLUniformManager& uman,
                          const GrDrawEffect& drawEffect) SK_OVERRIDE {}
 
 private:
     typedef GrGLVertexEffect INHERITED;
 };
 
 ///////////////////////////////////////////////////////////////////////////////
 
-GrCustomCoordsTextureEffect::GrCustomCoordsTextureEffect(GrTexture* texture,
+GrDistanceFieldTextureEffect::GrDistanceFieldTextureEffect(GrTexture* texture,
                                                          const GrTextureParams& params)
     : fTextureAccess(texture, params) {
     this->addTextureAccess(&fTextureAccess);
     this->addVertexAttrib(kVec2f_GrSLType);
 }
 
-bool GrCustomCoordsTextureEffect::onIsEqual(const GrEffect& other) const {
-    const GrCustomCoordsTextureEffect& cte = CastEffect<GrCustomCoordsTextureEffect>(other);
+bool GrDistanceFieldTextureEffect::onIsEqual(const GrEffect& other) const {
+    const GrDistanceFieldTextureEffect& cte = CastEffect<GrDistanceFieldTextureEffect>(other);
     return fTextureAccess == cte.fTextureAccess;
 }
 
-void GrCustomCoordsTextureEffect::getConstantColorComponents(GrColor* color,
+void GrDistanceFieldTextureEffect::getConstantColorComponents(GrColor* color,
                                                              uint32_t* validFlags) const {
     if ((*validFlags & kA_GrColorComponentFlag) && 0xFF == GrColorUnpackA(*color) &&
         GrPixelConfigIsOpaque(this->texture(0)->config())) {
         *validFlags = kA_GrColorComponentFlag;
     } else {
         *validFlags = 0;
     }
 }
 
-const GrBackendEffectFactory& GrCustomCoordsTextureEffect::getFactory() const {
-    return GrTBackendEffectFactory<GrCustomCoordsTextureEffect>::getInstance();
+const GrBackendEffectFactory& GrDistanceFieldTextureEffect::getFactory() const {
+    return GrTBackendEffectFactory<GrDistanceFieldTextureEffect>::getInstance();
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 
-GR_DEFINE_EFFECT_TEST(GrCustomCoordsTextureEffect);
+GR_DEFINE_EFFECT_TEST(GrDistanceFieldTextureEffect);
 
-GrEffectRef* GrCustomCoordsTextureEffect::TestCreate(SkRandom* random,
+GrEffectRef* GrDistanceFieldTextureEffect::TestCreate(SkRandom* random,
                                                      GrContext*,
                                                      const GrDrawTargetCaps&,
                                                      GrTexture* textures[]) {
     int texIdx = random->nextBool() ? GrEffectUnitTest::kSkiaPMTextureIdx :
                                       GrEffectUnitTest::kAlphaTextureIdx;
     static const SkShader::TileMode kTileModes[] = {
         SkShader::kClamp_TileMode,
         SkShader::kRepeat_TileMode,
         SkShader::kMirror_TileMode,
     };
     SkShader::TileMode tileModes[] = {
         kTileModes[random->nextULessThan(SK_ARRAY_COUNT(kTileModes))],
         kTileModes[random->nextULessThan(SK_ARRAY_COUNT(kTileModes))],
     };
     GrTextureParams params(tileModes, random->nextBool() ? GrTextureParams::kBilerp_FilterMode :
                                                            GrTextureParams::kNone_FilterMode);
 
-    return GrCustomCoordsTextureEffect::Create(textures[texIdx], params);
+    return GrDistanceFieldTextureEffect::Create(textures[texIdx], params);
 }