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      1 /*
      2  * Copyright 2013 Google Inc.
      3  *
      4  * Use of this source code is governed by a BSD-style license that can be
      5  * found in the LICENSE file.
      6  */
      7 
      8 #include "GrDistanceFieldTextureEffect.h"
      9 #include "gl/GrGLEffect.h"
     10 #include "gl/GrGLSL.h"
     11 #include "gl/GrGLTexture.h"
     12 #include "gl/GrGLVertexEffect.h"
     13 #include "GrTBackendEffectFactory.h"
     14 #include "GrTexture.h"
     15 
     16 // The distance field is constructed as unsigned char values, so that the zero value is at 128.
     17 // Hence our zero threshold is 128/255.
     18 #define THRESHOLD "0.50196078431"
     19 
     20 class GrGLDistanceFieldTextureEffect : public GrGLVertexEffect {
     21 public:
     22     GrGLDistanceFieldTextureEffect(const GrBackendEffectFactory& factory, const GrDrawEffect& drawEffect)
     23         : INHERITED (factory) {}
     24 
     25     virtual void emitCode(GrGLFullShaderBuilder* builder,
     26                           const GrDrawEffect& drawEffect,
     27                           EffectKey key,
     28                           const char* outputColor,
     29                           const char* inputColor,
     30                           const TransformedCoordsArray&,
     31                           const TextureSamplerArray& samplers) SK_OVERRIDE {
     32         SkASSERT(1 == drawEffect.castEffect<GrDistanceFieldTextureEffect>().numVertexAttribs());
     33 
     34         SkString fsCoordName;
     35         const char* vsVaryingName;
     36         const char* fsVaryingNamePtr;
     37         builder->addVarying(kVec2f_GrSLType, "textureCoords", &vsVaryingName, &fsVaryingNamePtr);
     38         fsCoordName = fsVaryingNamePtr;
     39 
     40         const char* attrName =
     41             builder->getEffectAttributeName(drawEffect.getVertexAttribIndices()[0])->c_str();
     42         builder->vsCodeAppendf("\t%s = %s;\n", vsVaryingName, attrName);
     43 
     44         builder->fsCodeAppend("\tvec4 texColor = ");
     45         builder->fsAppendTextureLookup(samplers[0],
     46                                        fsCoordName.c_str(),
     47                                        kVec2f_GrSLType);
     48         builder->fsCodeAppend(";\n");
     49         builder->fsCodeAppend("\tfloat distance = texColor.r;\n");
     50         // this gives us a smooth step across approximately one fragment
     51         // (assuming a radius of the diagonal of the fragment, hence a factor of sqrt(2)/2)
     52         builder->fsCodeAppend("\tfloat afwidth = 0.7071*length(vec2(dFdx(distance), dFdy(distance)));\n");
     53         builder->fsCodeAppend("\tfloat val = smoothstep("THRESHOLD"-afwidth, "THRESHOLD"+afwidth, distance);\n");
     54 
     55         builder->fsCodeAppendf("\t%s = %s;\n", outputColor,
     56                                    (GrGLSLExpr4(inputColor) * GrGLSLExpr1("val")).c_str());
     57     }
     58 
     59     virtual void setData(const GrGLUniformManager& uman,
     60                          const GrDrawEffect& drawEffect) SK_OVERRIDE {}
     61 
     62 private:
     63     typedef GrGLVertexEffect INHERITED;
     64 };
     65 
     66 ///////////////////////////////////////////////////////////////////////////////
     67 
     68 GrDistanceFieldTextureEffect::GrDistanceFieldTextureEffect(GrTexture* texture,
     69                                                          const GrTextureParams& params)
     70     : fTextureAccess(texture, params) {
     71     this->addTextureAccess(&fTextureAccess);
     72     this->addVertexAttrib(kVec2f_GrSLType);
     73 }
     74 
     75 bool GrDistanceFieldTextureEffect::onIsEqual(const GrEffect& other) const {
     76     const GrDistanceFieldTextureEffect& cte = CastEffect<GrDistanceFieldTextureEffect>(other);
     77     return fTextureAccess == cte.fTextureAccess;
     78 }
     79 
     80 void GrDistanceFieldTextureEffect::getConstantColorComponents(GrColor* color,
     81                                                              uint32_t* validFlags) const {
     82     if ((*validFlags & kA_GrColorComponentFlag) && 0xFF == GrColorUnpackA(*color) &&
     83         GrPixelConfigIsOpaque(this->texture(0)->config())) {
     84         *validFlags = kA_GrColorComponentFlag;
     85     } else {
     86         *validFlags = 0;
     87     }
     88 }
     89 
     90 const GrBackendEffectFactory& GrDistanceFieldTextureEffect::getFactory() const {
     91     return GrTBackendEffectFactory<GrDistanceFieldTextureEffect>::getInstance();
     92 }
     93 
     94 ///////////////////////////////////////////////////////////////////////////////
     95 
     96 GR_DEFINE_EFFECT_TEST(GrDistanceFieldTextureEffect);
     97 
     98 GrEffectRef* GrDistanceFieldTextureEffect::TestCreate(SkRandom* random,
     99                                                      GrContext*,
    100                                                      const GrDrawTargetCaps&,
    101                                                      GrTexture* textures[]) {
    102     int texIdx = random->nextBool() ? GrEffectUnitTest::kSkiaPMTextureIdx :
    103                                       GrEffectUnitTest::kAlphaTextureIdx;
    104     static const SkShader::TileMode kTileModes[] = {
    105         SkShader::kClamp_TileMode,
    106         SkShader::kRepeat_TileMode,
    107         SkShader::kMirror_TileMode,
    108     };
    109     SkShader::TileMode tileModes[] = {
    110         kTileModes[random->nextULessThan(SK_ARRAY_COUNT(kTileModes))],
    111         kTileModes[random->nextULessThan(SK_ARRAY_COUNT(kTileModes))],
    112     };
    113     GrTextureParams params(tileModes, random->nextBool() ? GrTextureParams::kBilerp_FilterMode :
    114                                                            GrTextureParams::kNone_FilterMode);
    115 
    116     return GrDistanceFieldTextureEffect::Create(textures[texIdx], params);
    117 }
    118