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 "GrDistanceFieldTextureEffect.h"
#include "gl/GrGLEffect.h"
#include "gl/GrGLSL.h"
#include "gl/GrGLTexture.h"
#include "gl/GrGLVertexEffect.h"
#include "GrTBackendEffectFactory.h"
#include "GrTexture.h"

// The distance field is constructed as unsigned char values, so that the zero value is at 128,
// and the range is [-4, 4 - 1/255). Hence our multiplier is 8 - 1/32 and zero threshold is 128/255.
#define MULTIPLIER "7.96875"
#define THRESHOLD "0.50196078431"

class GrGLDistanceFieldTextureEffect : public GrGLVertexEffect {
public:
    GrGLDistanceFieldTextureEffect(const GrBackendEffectFactory& factory,
                                   const GrDrawEffect& drawEffect)
        : INHERITED (factory)
        , fTextureSize(SkISize::Make(-1,-1)) {}

    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<GrDistanceFieldTextureEffect>().numVertexAttribs());

        SkAssertResult(builder->enableFeature(GrGLShaderBuilder::kStandardDerivatives_GLSLFeature));
        const GrDistanceFieldTextureEffect& dfTexEffect =
                                              drawEffect.castEffect<GrDistanceFieldTextureEffect>();

        SkString fsCoordName;
        const char* vsCoordName;
        const char* fsCoordNamePtr;
        builder->addVarying(kVec2f_GrSLType, "textureCoords", &vsCoordName, &fsCoordNamePtr);
        fsCoordName = fsCoordNamePtr;

        const char* attrName0 =
            builder->getEffectAttributeName(drawEffect.getVertexAttribIndices()[0])->c_str();
        builder->vsCodeAppendf("\t%s = %s;\n", vsCoordName, attrName0);

        const char* textureSizeUniName = NULL;
        fTextureSizeUni = builder->addUniform(GrGLShaderBuilder::kFragment_Visibility,
                                              kVec2f_GrSLType, "TextureSize",
                                              &textureSizeUniName);

        builder->fsCodeAppend("\tvec4 texColor = ");
        builder->fsAppendTextureLookup(samplers[0],
                                       fsCoordName.c_str(),
                                       kVec2f_GrSLType);
        builder->fsCodeAppend(";\n");
        builder->fsCodeAppend("\tfloat distance = " MULTIPLIER "*(texColor.r - " THRESHOLD ");\n");

        // we adjust for the effect of the transformation on the distance by using
        // the length of the gradient of the texture coordinates. We use st coordinates
        // to ensure we're mapping 1:1 from texel space to pixel space.
        builder->fsCodeAppendf("\tvec2 uv = %s;\n", fsCoordName.c_str());
        builder->fsCodeAppendf("\tvec2 st = uv*%s;\n", textureSizeUniName);
        builder->fsCodeAppend("\tfloat afwidth;\n");
        if (dfTexEffect.isSimilarity()) {
            // 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("\tafwidth = 0.7071*dFdx(st.x);\n");
        } else {
            builder->fsCodeAppend("\tvec2 Jdx = dFdx(st);\n");
            builder->fsCodeAppend("\tvec2 Jdy = dFdy(st);\n");

            builder->fsCodeAppend("\tvec2 uv_grad;\n");
            if (builder->ctxInfo().caps()->dropsTileOnZeroDivide()) {
                // this is to compensate for the Adreno, which likes to drop tiles on division by 0
                builder->fsCodeAppend("\tfloat uv_len2 = dot(uv, uv);\n");
                builder->fsCodeAppend("\tif (uv_len2 < 0.0001) {\n");
                builder->fsCodeAppend("\t\tuv_grad = vec2(0.7071, 0.7071);\n");
                builder->fsCodeAppend("\t} else {\n");
                builder->fsCodeAppend("\t\tuv_grad = uv*inversesqrt(uv_len2);\n");
                builder->fsCodeAppend("\t}\n");
            } else {
                builder->fsCodeAppend("\tuv_grad = normalize(uv);\n");
            }
            builder->fsCodeAppend("\tvec2 grad = vec2(uv_grad.x*Jdx.x + uv_grad.y*Jdy.x,\n");
            builder->fsCodeAppend("\t                 uv_grad.x*Jdx.y + uv_grad.y*Jdy.y);\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("\tafwidth = 0.7071*length(grad);\n");
        }

        builder->fsCodeAppend("\tfloat val = smoothstep(-afwidth, 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 {
        SkASSERT(fTextureSizeUni.isValid());

        GrTexture* texture = drawEffect.effect()->get()->texture(0);
        if (texture->width() != fTextureSize.width() ||
            texture->height() != fTextureSize.height()) {
            fTextureSize = SkISize::Make(texture->width(), texture->height());
            uman.set2f(fTextureSizeUni,
                       SkIntToScalar(fTextureSize.width()),
                       SkIntToScalar(fTextureSize.height()));
        }
    }

    static inline EffectKey GenKey(const GrDrawEffect& drawEffect, const GrGLCaps&) {
        const GrDistanceFieldTextureEffect& dfTexEffect =
                                              drawEffect.castEffect<GrDistanceFieldTextureEffect>();

        return dfTexEffect.isSimilarity() ? 0x1 : 0x0;
    }

private:
    GrGLUniformManager::UniformHandle fTextureSizeUni;
    SkISize                           fTextureSize;

    typedef GrGLVertexEffect INHERITED;
};

///////////////////////////////////////////////////////////////////////////////

GrDistanceFieldTextureEffect::GrDistanceFieldTextureEffect(GrTexture* texture,
                                                           const GrTextureParams& params,
                                                           bool similarity)
    : fTextureAccess(texture, params)
    , fIsSimilarity(similarity) {
    this->addTextureAccess(&fTextureAccess);
    this->addVertexAttrib(kVec2f_GrSLType);
}

bool GrDistanceFieldTextureEffect::onIsEqual(const GrEffect& other) const {
    const GrDistanceFieldTextureEffect& cte = CastEffect<GrDistanceFieldTextureEffect>(other);
    return fTextureAccess == cte.fTextureAccess;
}

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& GrDistanceFieldTextureEffect::getFactory() const {
    return GrTBackendEffectFactory<GrDistanceFieldTextureEffect>::getInstance();
}

///////////////////////////////////////////////////////////////////////////////

GR_DEFINE_EFFECT_TEST(GrDistanceFieldTextureEffect);

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 GrDistanceFieldTextureEffect::Create(textures[texIdx], params,
                                                random->nextBool());
}

///////////////////////////////////////////////////////////////////////////////

class GrGLDistanceFieldLCDTextureEffect : public GrGLVertexEffect {
public:
    GrGLDistanceFieldLCDTextureEffect(const GrBackendEffectFactory& factory,
                                      const GrDrawEffect& drawEffect)
    : INHERITED (factory)
    , fTextureSize(SkISize::Make(-1,-1)) {}

    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<GrDistanceFieldLCDTextureEffect>().numVertexAttribs());

        SkAssertResult(builder->enableFeature(GrGLShaderBuilder::kStandardDerivatives_GLSLFeature));
        const GrDistanceFieldLCDTextureEffect& dfTexEffect =
                                           drawEffect.castEffect<GrDistanceFieldLCDTextureEffect>();

        SkString fsCoordName;
        const char* vsCoordName;
        const char* fsCoordNamePtr;
        builder->addVarying(kVec2f_GrSLType, "textureCoords", &vsCoordName, &fsCoordNamePtr);
        fsCoordName = fsCoordNamePtr;

        const char* attrName0 =
        builder->getEffectAttributeName(drawEffect.getVertexAttribIndices()[0])->c_str();
        builder->vsCodeAppendf("\t%s = %s;\n", vsCoordName, attrName0);

        const char* textureSizeUniName = NULL;
        // width, height, 1/(3*width)
        fTextureSizeUni = builder->addUniform(GrGLShaderBuilder::kFragment_Visibility,
                                              kVec3f_GrSLType, "TextureSize",
                                              &textureSizeUniName);

        // create LCD offset adjusted by inverse of transform
        builder->fsCodeAppendf("\tvec2 uv = %s;\n", fsCoordName.c_str());
        builder->fsCodeAppendf("\tvec2 st = uv*%s.xy;\n", textureSizeUniName);
        if (dfTexEffect.isUniformScale()) {
            builder->fsCodeAppend("\tfloat dx = dFdx(st.x);\n");
            builder->fsCodeAppendf("\tvec2 offset = vec2(dx*%s.z, 0.0);\n", textureSizeUniName);
        } else {
            builder->fsCodeAppend("\tvec2 Jdx = dFdx(st);\n");
            builder->fsCodeAppend("\tvec2 Jdy = dFdy(st);\n");
            builder->fsCodeAppendf("\tvec2 offset = %s.z*Jdx;\n", textureSizeUniName);
        }

        // green is distance to uv center
        builder->fsCodeAppend("\tvec4 texColor = ");
        builder->fsAppendTextureLookup(samplers[0], "uv", kVec2f_GrSLType);
        builder->fsCodeAppend(";\n");
        builder->fsCodeAppend("\tvec3 distance;\n");
        builder->fsCodeAppend("\tdistance.y = " MULTIPLIER "*(texColor.r - " THRESHOLD ");\n");
        // red is distance to left offset
        builder->fsCodeAppend("\tvec2 uv_adjusted = uv - offset;\n");
        builder->fsCodeAppend("\ttexColor = ");
        builder->fsAppendTextureLookup(samplers[0], "uv_adjusted", kVec2f_GrSLType);
        builder->fsCodeAppend(";\n");
        builder->fsCodeAppend("\tdistance.x = " MULTIPLIER "*(texColor.r - " THRESHOLD ");\n");
        // blue is distance to right offset
        builder->fsCodeAppend("\tuv_adjusted = uv + offset;\n");
        builder->fsCodeAppend("\ttexColor = ");
        builder->fsAppendTextureLookup(samplers[0], "uv_adjusted", kVec2f_GrSLType);
        builder->fsCodeAppend(";\n");
        builder->fsCodeAppend("\tdistance.z = " MULTIPLIER "*(texColor.r - " THRESHOLD ");\n");

        // we adjust for the effect of the transformation on the distance by using
        // the length of the gradient of the texture coordinates. We use st coordinates
        // to ensure we're mapping 1:1 from texel space to pixel space.

        // To be strictly correct, we should compute the anti-aliasing factor separately
        // for each color component. However, this is only important when using perspective
        // transformations, and even then using a single factor seems like a reasonable
        // trade-off between quality and speed.
        builder->fsCodeAppend("\tfloat afwidth;\n");
        if (dfTexEffect.isUniformScale()) {
            // 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("\tafwidth = 0.7071*dx;\n");
        } else {
            builder->fsCodeAppend("\tvec2 uv_grad;\n");
            if (builder->ctxInfo().caps()->dropsTileOnZeroDivide()) {
                // this is to compensate for the Adreno, which likes to drop tiles on division by 0
                builder->fsCodeAppend("\tfloat uv_len2 = dot(uv, uv);\n");
                builder->fsCodeAppend("\tif (uv_len2 < 0.0001) {\n");
                builder->fsCodeAppend("\t\tuv_grad = vec2(0.7071, 0.7071);\n");
                builder->fsCodeAppend("\t} else {\n");
                builder->fsCodeAppend("\t\tuv_grad = uv*inversesqrt(uv_len2);\n");
                builder->fsCodeAppend("\t}\n");
            } else {
                builder->fsCodeAppend("\tuv_grad = normalize(uv);\n");
            }
            builder->fsCodeAppend("\tvec2 grad = vec2(uv_grad.x*Jdx.x + uv_grad.y*Jdy.x,\n");
            builder->fsCodeAppend("\t                 uv_grad.x*Jdx.y + uv_grad.y*Jdy.y);\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("\tafwidth = 0.7071*length(grad);\n");
        }

        builder->fsCodeAppend("\tvec4 val = vec4(smoothstep(vec3(-afwidth), vec3(afwidth), distance), 1.0);\n");

        builder->fsCodeAppendf("\t%s = %s;\n", outputColor,
                               (GrGLSLExpr4(inputColor) * GrGLSLExpr4("val")).c_str());
    }

    virtual void setData(const GrGLUniformManager& uman,
                         const GrDrawEffect& drawEffect) SK_OVERRIDE {
        SkASSERT(fTextureSizeUni.isValid());

        GrTexture* texture = drawEffect.effect()->get()->texture(0);
        if (texture->width() != fTextureSize.width() ||
            texture->height() != fTextureSize.height()) {
            const GrDistanceFieldLCDTextureEffect& dfTexEffect =
                                           drawEffect.castEffect<GrDistanceFieldLCDTextureEffect>();
            fTextureSize = SkISize::Make(texture->width(), texture->height());
            float delta = 1.0f/(3.0f*texture->width());
            if (dfTexEffect.useBGR()) {
                delta = -delta;
            }
            uman.set3f(fTextureSizeUni,
                       SkIntToScalar(fTextureSize.width()),
                       SkIntToScalar(fTextureSize.height()),
                       delta);
        }
    }

    static inline EffectKey GenKey(const GrDrawEffect& drawEffect, const GrGLCaps&) {
        const GrDistanceFieldLCDTextureEffect& dfTexEffect =
                                           drawEffect.castEffect<GrDistanceFieldLCDTextureEffect>();

        int uniformScale = dfTexEffect.isUniformScale() ? 0x01 : 0x00;
        int useBGR = dfTexEffect.useBGR() ? 0x10 : 0x00;
        return uniformScale | useBGR;
    }

private:
    GrGLUniformManager::UniformHandle fTextureSizeUni;
    SkISize                           fTextureSize;

    typedef GrGLVertexEffect INHERITED;
};

///////////////////////////////////////////////////////////////////////////////

GrDistanceFieldLCDTextureEffect::GrDistanceFieldLCDTextureEffect(GrTexture* texture,
                                                                 const GrTextureParams& params,
                                                                 bool uniformScale,
                                                                 bool useBGR)
    : fTextureAccess(texture, params)
    , fUniformScale(uniformScale)
    , fUseBGR(useBGR) {
    this->addTextureAccess(&fTextureAccess);
    this->addVertexAttrib(kVec2f_GrSLType);
}

bool GrDistanceFieldLCDTextureEffect::onIsEqual(const GrEffect& other) const {
    const GrDistanceFieldLCDTextureEffect& cte = CastEffect<GrDistanceFieldLCDTextureEffect>(other);
    return fTextureAccess == cte.fTextureAccess;
}

void GrDistanceFieldLCDTextureEffect::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& GrDistanceFieldLCDTextureEffect::getFactory() const {
    return GrTBackendEffectFactory<GrDistanceFieldLCDTextureEffect>::getInstance();
}

///////////////////////////////////////////////////////////////////////////////

GR_DEFINE_EFFECT_TEST(GrDistanceFieldLCDTextureEffect);

GrEffectRef* GrDistanceFieldLCDTextureEffect::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 GrDistanceFieldLCDTextureEffect::Create(textures[texIdx], params,
                                                   random->nextBool(), random->nextBool());
}