path: root/src/effects/SkDisplacementMapEffect.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 "SkDisplacementMapEffect.h"

#include "SkBitmap.h"
#include "SkReadBuffer.h"
#include "SkSpecialImage.h"
#include "SkWriteBuffer.h"
#include "SkUnPreMultiply.h"
#include "SkColorPriv.h"
#if SK_SUPPORT_GPU
#include "GrContext.h"
#include "GrDrawContext.h"
#include "GrCoordTransform.h"
#include "GrInvariantOutput.h"
#include "SkGr.h"
#include "effects/GrTextureDomain.h"
#include "glsl/GrGLSLFragmentProcessor.h"
#include "glsl/GrGLSLFragmentShaderBuilder.h"
#include "glsl/GrGLSLProgramDataManager.h"
#include "glsl/GrGLSLUniformHandler.h"
#endif

namespace {

#define kChannelSelectorKeyBits 3; // Max value is 4, so 3 bits are required at most

template<SkDisplacementMapEffect::ChannelSelectorType type>
uint32_t getValue(SkColor, const SkUnPreMultiply::Scale*) {
    SkDEBUGFAIL("Unknown channel selector");
    return 0;
}

template<> uint32_t getValue<SkDisplacementMapEffect::kR_ChannelSelectorType>(
    SkColor l, const SkUnPreMultiply::Scale* table) {
    return SkUnPreMultiply::ApplyScale(table[SkGetPackedA32(l)], SkGetPackedR32(l));
}

template<> uint32_t getValue<SkDisplacementMapEffect::kG_ChannelSelectorType>(
    SkColor l, const SkUnPreMultiply::Scale* table) {
    return SkUnPreMultiply::ApplyScale(table[SkGetPackedA32(l)], SkGetPackedG32(l));
}

template<> uint32_t getValue<SkDisplacementMapEffect::kB_ChannelSelectorType>(
    SkColor l, const SkUnPreMultiply::Scale* table) {
    return SkUnPreMultiply::ApplyScale(table[SkGetPackedA32(l)], SkGetPackedB32(l));
}

template<> uint32_t getValue<SkDisplacementMapEffect::kA_ChannelSelectorType>(
    SkColor l, const SkUnPreMultiply::Scale*) {
    return SkGetPackedA32(l);
}

template<SkDisplacementMapEffect::ChannelSelectorType typeX,
         SkDisplacementMapEffect::ChannelSelectorType typeY>
void computeDisplacement(const SkVector& scale, SkBitmap* dst,
                         const SkBitmap& displ, const SkIPoint& offset,
                         const SkBitmap& src,
                         const SkIRect& bounds) {
    static const SkScalar Inv8bit = SkScalarInvert(255);
    const int srcW = src.width();
    const int srcH = src.height();
    const SkVector scaleForColor = SkVector::Make(SkScalarMul(scale.fX, Inv8bit),
                                                  SkScalarMul(scale.fY, Inv8bit));
    const SkVector scaleAdj = SkVector::Make(SK_ScalarHalf - SkScalarMul(scale.fX, SK_ScalarHalf),
                                             SK_ScalarHalf - SkScalarMul(scale.fY, SK_ScalarHalf));
    const SkUnPreMultiply::Scale* table = SkUnPreMultiply::GetScaleTable();
    SkPMColor* dstPtr = dst->getAddr32(0, 0);
    for (int y = bounds.top(); y < bounds.bottom(); ++y) {
        const SkPMColor* displPtr = displ.getAddr32(bounds.left() + offset.fX, y + offset.fY);
        for (int x = bounds.left(); x < bounds.right(); ++x, ++displPtr) {
            const SkScalar displX = SkScalarMul(scaleForColor.fX,
                SkIntToScalar(getValue<typeX>(*displPtr, table))) + scaleAdj.fX;
            const SkScalar displY = SkScalarMul(scaleForColor.fY,
                SkIntToScalar(getValue<typeY>(*displPtr, table))) + scaleAdj.fY;
            // Truncate the displacement values
            const int srcX = x + SkScalarTruncToInt(displX);
            const int srcY = y + SkScalarTruncToInt(displY);
            *dstPtr++ = ((srcX < 0) || (srcX >= srcW) || (srcY < 0) || (srcY >= srcH)) ?
                      0 : *(src.getAddr32(srcX, srcY));
        }
    }
}

template<SkDisplacementMapEffect::ChannelSelectorType typeX>
void computeDisplacement(SkDisplacementMapEffect::ChannelSelectorType yChannelSelector,
                         const SkVector& scale, SkBitmap* dst,
                         const SkBitmap& displ, const SkIPoint& offset,
                         const SkBitmap& src,
                         const SkIRect& bounds) {
    switch (yChannelSelector) {
      case SkDisplacementMapEffect::kR_ChannelSelectorType:
        computeDisplacement<typeX, SkDisplacementMapEffect::kR_ChannelSelectorType>(
            scale, dst, displ, offset, src, bounds);
        break;
      case SkDisplacementMapEffect::kG_ChannelSelectorType:
        computeDisplacement<typeX, SkDisplacementMapEffect::kG_ChannelSelectorType>(
            scale, dst, displ, offset, src, bounds);
        break;
      case SkDisplacementMapEffect::kB_ChannelSelectorType:
        computeDisplacement<typeX, SkDisplacementMapEffect::kB_ChannelSelectorType>(
            scale, dst, displ, offset, src, bounds);
        break;
      case SkDisplacementMapEffect::kA_ChannelSelectorType:
        computeDisplacement<typeX, SkDisplacementMapEffect::kA_ChannelSelectorType>(
            scale, dst, displ, offset, src, bounds);
        break;
      case SkDisplacementMapEffect::kUnknown_ChannelSelectorType:
      default:
        SkDEBUGFAIL("Unknown Y channel selector");
    }
}

void computeDisplacement(SkDisplacementMapEffect::ChannelSelectorType xChannelSelector,
                         SkDisplacementMapEffect::ChannelSelectorType yChannelSelector,
                         const SkVector& scale, SkBitmap* dst,
                         const SkBitmap& displ, const SkIPoint& offset,
                         const SkBitmap& src,
                         const SkIRect& bounds) {
    switch (xChannelSelector) {
      case SkDisplacementMapEffect::kR_ChannelSelectorType:
        computeDisplacement<SkDisplacementMapEffect::kR_ChannelSelectorType>(
            yChannelSelector, scale, dst, displ, offset, src, bounds);
        break;
      case SkDisplacementMapEffect::kG_ChannelSelectorType:
        computeDisplacement<SkDisplacementMapEffect::kG_ChannelSelectorType>(
            yChannelSelector, scale, dst, displ, offset, src, bounds);
        break;
      case SkDisplacementMapEffect::kB_ChannelSelectorType:
        computeDisplacement<SkDisplacementMapEffect::kB_ChannelSelectorType>(
            yChannelSelector, scale, dst, displ, offset, src, bounds);
        break;
      case SkDisplacementMapEffect::kA_ChannelSelectorType:
        computeDisplacement<SkDisplacementMapEffect::kA_ChannelSelectorType>(
            yChannelSelector, scale, dst, displ, offset, src, bounds);
        break;
      case SkDisplacementMapEffect::kUnknown_ChannelSelectorType:
      default:
        SkDEBUGFAIL("Unknown X channel selector");
    }
}

bool channel_selector_type_is_valid(SkDisplacementMapEffect::ChannelSelectorType cst) {
    switch (cst) {
    case SkDisplacementMapEffect::kUnknown_ChannelSelectorType:
    case SkDisplacementMapEffect::kR_ChannelSelectorType:
    case SkDisplacementMapEffect::kG_ChannelSelectorType:
    case SkDisplacementMapEffect::kB_ChannelSelectorType:
    case SkDisplacementMapEffect::kA_ChannelSelectorType:
        return true;
    default:
        break;
    }
    return false;
}

} // end namespace

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

sk_sp<SkImageFilter> SkDisplacementMapEffect::Make(ChannelSelectorType xChannelSelector,
                                                   ChannelSelectorType yChannelSelector,
                                                   SkScalar scale,
                                                   sk_sp<SkImageFilter> displacement,
                                                   sk_sp<SkImageFilter> color,
                                                   const CropRect* cropRect) {
    if (!channel_selector_type_is_valid(xChannelSelector) ||
        !channel_selector_type_is_valid(yChannelSelector)) {
        return nullptr;
    }

    sk_sp<SkImageFilter> inputs[2] = { std::move(displacement), std::move(color) };
    return sk_sp<SkImageFilter>(new SkDisplacementMapEffect(xChannelSelector,
                                                            yChannelSelector,
                                                            scale, inputs, cropRect));
}

SkDisplacementMapEffect::SkDisplacementMapEffect(ChannelSelectorType xChannelSelector,
                                                 ChannelSelectorType yChannelSelector,
                                                 SkScalar scale,
                                                 sk_sp<SkImageFilter> inputs[2],
                                                 const CropRect* cropRect)
    : INHERITED(inputs, 2, cropRect)
    , fXChannelSelector(xChannelSelector)
    , fYChannelSelector(yChannelSelector)
    , fScale(scale) {
}

SkDisplacementMapEffect::~SkDisplacementMapEffect() {
}

sk_sp<SkFlattenable> SkDisplacementMapEffect::CreateProc(SkReadBuffer& buffer) {
    SK_IMAGEFILTER_UNFLATTEN_COMMON(common, 2);
    ChannelSelectorType xsel = (ChannelSelectorType)buffer.readInt();
    ChannelSelectorType ysel = (ChannelSelectorType)buffer.readInt();
    SkScalar scale = buffer.readScalar();
    return Make(xsel, ysel, scale,
                common.getInput(0), common.getInput(1),
                &common.cropRect());
}

void SkDisplacementMapEffect::flatten(SkWriteBuffer& buffer) const {
    this->INHERITED::flatten(buffer);
    buffer.writeInt((int) fXChannelSelector);
    buffer.writeInt((int) fYChannelSelector);
    buffer.writeScalar(fScale);
}

#if SK_SUPPORT_GPU
class GrDisplacementMapEffect : public GrFragmentProcessor {
public:
    static sk_sp<GrFragmentProcessor> Make(
                SkDisplacementMapEffect::ChannelSelectorType xChannelSelector,
                SkDisplacementMapEffect::ChannelSelectorType yChannelSelector, SkVector scale,
                GrTexture* displacement, const SkMatrix& offsetMatrix, GrTexture* color,
                const SkISize& colorDimensions) {
        return sk_sp<GrFragmentProcessor>(
            new GrDisplacementMapEffect(xChannelSelector, yChannelSelector, scale, displacement,
                                        offsetMatrix, color, colorDimensions));
    }

    virtual ~GrDisplacementMapEffect();

    SkDisplacementMapEffect::ChannelSelectorType xChannelSelector() const {
        return fXChannelSelector;
    }
    SkDisplacementMapEffect::ChannelSelectorType yChannelSelector() const {
        return fYChannelSelector;
    }
    const SkVector& scale() const { return fScale; }

    const char* name() const override { return "DisplacementMap"; }
    const GrTextureDomain& domain() const { return fDomain; }

private:
    GrGLSLFragmentProcessor* onCreateGLSLInstance() const override;

    void onGetGLSLProcessorKey(const GrGLSLCaps& caps, GrProcessorKeyBuilder* b) const override;

    bool onIsEqual(const GrFragmentProcessor&) const override;

    void onComputeInvariantOutput(GrInvariantOutput* inout) const override;

    GrDisplacementMapEffect(SkDisplacementMapEffect::ChannelSelectorType xChannelSelector,
                            SkDisplacementMapEffect::ChannelSelectorType yChannelSelector,
                            const SkVector& scale,
                            GrTexture* displacement, const SkMatrix& offsetMatrix,
                            GrTexture* color,
                            const SkISize& colorDimensions);

    GR_DECLARE_FRAGMENT_PROCESSOR_TEST;

    GrCoordTransform            fDisplacementTransform;
    GrTextureAccess             fDisplacementAccess;
    GrCoordTransform            fColorTransform;
    GrTextureDomain             fDomain;
    GrTextureAccess             fColorAccess;
    SkDisplacementMapEffect::ChannelSelectorType fXChannelSelector;
    SkDisplacementMapEffect::ChannelSelectorType fYChannelSelector;
    SkVector fScale;

    typedef GrFragmentProcessor INHERITED;
};
#endif

sk_sp<SkSpecialImage> SkDisplacementMapEffect::onFilterImage(SkSpecialImage* source,
                                                             const Context& ctx,
                                                             SkIPoint* offset) const {
    SkIPoint colorOffset = SkIPoint::Make(0, 0);
    sk_sp<SkSpecialImage> color(this->filterInput(1, source, ctx, &colorOffset));
    if (!color) {
        return nullptr;
    }

    SkIPoint displOffset = SkIPoint::Make(0, 0);
    sk_sp<SkSpecialImage> displ(this->filterInput(0, source, ctx, &displOffset));
    if (!displ) {
        return nullptr;
    }

    const SkIRect srcBounds = SkIRect::MakeXYWH(colorOffset.x(), colorOffset.y(),
                                                color->width(), color->height());

    // Both paths do bounds checking on color pixel access, we don't need to
    // pad the color bitmap to bounds here.
    SkIRect bounds;
    if (!this->applyCropRect(ctx, srcBounds, &bounds)) {
        return nullptr;
    }

    SkIRect displBounds;
    displ = this->applyCropRect(ctx, displ.get(), &displOffset, &displBounds);
    if (!displ) {
        return nullptr;
    }

    if (!bounds.intersect(displBounds)) {
        return nullptr;
    }

    const SkIRect colorBounds = bounds.makeOffset(-colorOffset.x(), -colorOffset.y());

    SkVector scale = SkVector::Make(fScale, fScale);
    ctx.ctm().mapVectors(&scale, 1);

#if SK_SUPPORT_GPU
    if (source->isTextureBacked()) {
        GrContext* context = source->getContext();

        sk_sp<GrTexture> colorTexture(color->asTextureRef(context));
        sk_sp<GrTexture> displTexture(displ->asTextureRef(context));
        if (!colorTexture || !displTexture) {
            return nullptr;
        }

        GrPaint paint;
        SkMatrix offsetMatrix = GrCoordTransform::MakeDivByTextureWHMatrix(displTexture.get());
        offsetMatrix.preTranslate(SkIntToScalar(colorOffset.fX - displOffset.fX),
                                  SkIntToScalar(colorOffset.fY - displOffset.fY));

        paint.addColorFragmentProcessor(
            GrDisplacementMapEffect::Make(fXChannelSelector,
                                          fYChannelSelector,
                                          scale,
                                          displTexture.get(),
                                          offsetMatrix,
                                          colorTexture.get(),
                                          SkISize::Make(color->width(), color->height())));
        paint.setPorterDuffXPFactory(SkXfermode::kSrc_Mode);
        SkMatrix matrix;
        matrix.setTranslate(-SkIntToScalar(colorBounds.x()), -SkIntToScalar(colorBounds.y()));

        sk_sp<GrDrawContext> drawContext(
            context->newDrawContext(SkBackingFit::kApprox, bounds.width(), bounds.height(),
                                    kSkia8888_GrPixelConfig, sk_ref_sp(source->getColorSpace())));
        if (!drawContext) {
            return nullptr;
        }

        drawContext->drawRect(GrNoClip(), paint, matrix, SkRect::Make(colorBounds));

        offset->fX = bounds.left();
        offset->fY = bounds.top();
        return SkSpecialImage::MakeFromGpu(SkIRect::MakeWH(bounds.width(), bounds.height()),
                                           kNeedNewImageUniqueID_SpecialImage,
                                           drawContext->asTexture(),
                                           sk_ref_sp(drawContext->getColorSpace()));
    }
#endif

    SkBitmap colorBM, displBM;

    if (!color->getROPixels(&colorBM) || !displ->getROPixels(&displBM)) {
        return nullptr;
    }

    if ((colorBM.colorType() != kN32_SkColorType) ||
        (displBM.colorType() != kN32_SkColorType)) {
        return nullptr;
    }

    SkAutoLockPixels colorLock(colorBM), displLock(displBM);
    if (!colorBM.getPixels() || !displBM.getPixels()) {
        return nullptr;
    }

    SkImageInfo info = SkImageInfo::MakeN32(bounds.width(), bounds.height(),
                                            colorBM.alphaType());

    SkBitmap dst;
    if (!dst.tryAllocPixels(info)) {
        return nullptr;
    }

    SkAutoLockPixels dstLock(dst);

    computeDisplacement(fXChannelSelector, fYChannelSelector, scale, &dst,
                        displBM, colorOffset - displOffset, colorBM, colorBounds);

    offset->fX = bounds.left();
    offset->fY = bounds.top();
    return SkSpecialImage::MakeFromRaster(SkIRect::MakeWH(bounds.width(), bounds.height()),
                                          dst);
}

SkRect SkDisplacementMapEffect::computeFastBounds(const SkRect& src) const {
    SkRect bounds = this->getColorInput() ? this->getColorInput()->computeFastBounds(src) : src;
    bounds.outset(SkScalarAbs(fScale) * SK_ScalarHalf, SkScalarAbs(fScale) * SK_ScalarHalf);
    return bounds;
}

SkIRect SkDisplacementMapEffect::onFilterNodeBounds(const SkIRect& src, const SkMatrix& ctm,
                                                    MapDirection) const {
    SkVector scale = SkVector::Make(fScale, fScale);
    ctm.mapVectors(&scale, 1);
    return src.makeOutset(SkScalarCeilToInt(SkScalarAbs(scale.fX) * SK_ScalarHalf),
                          SkScalarCeilToInt(SkScalarAbs(scale.fY) * SK_ScalarHalf));
}

SkIRect SkDisplacementMapEffect::onFilterBounds(const SkIRect& src, const SkMatrix& ctm,
                                                MapDirection direction) const {
    // Recurse only into color input.
    if (this->getColorInput()) {
        return this->getColorInput()->filterBounds(src, ctm, direction);
    }
    return src;
}

#ifndef SK_IGNORE_TO_STRING
void SkDisplacementMapEffect::toString(SkString* str) const {
    str->appendf("SkDisplacementMapEffect: (");
    str->appendf("scale: %f ", fScale);
    str->appendf("displacement: (");
    if (this->getDisplacementInput()) {
        this->getDisplacementInput()->toString(str);
    }
    str->appendf(") color: (");
    if (this->getColorInput()) {
        this->getColorInput()->toString(str);
    }
    str->appendf("))");
}
#endif

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

#if SK_SUPPORT_GPU
class GrGLDisplacementMapEffect : public GrGLSLFragmentProcessor {
public:
    void emitCode(EmitArgs&) override;

    static inline void GenKey(const GrProcessor&, const GrGLSLCaps&, GrProcessorKeyBuilder*);

protected:
    void onSetData(const GrGLSLProgramDataManager&, const GrProcessor&) override;

private:
    GrGLSLProgramDataManager::UniformHandle fScaleUni;
    GrTextureDomain::GLDomain fGLDomain;

    typedef GrGLSLFragmentProcessor INHERITED;
};

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

GrGLSLFragmentProcessor* GrDisplacementMapEffect::onCreateGLSLInstance() const {
    return new GrGLDisplacementMapEffect;
}

void GrDisplacementMapEffect::onGetGLSLProcessorKey(const GrGLSLCaps& caps,
                                                    GrProcessorKeyBuilder* b) const {
    GrGLDisplacementMapEffect::GenKey(*this, caps, b);
}

GrDisplacementMapEffect::GrDisplacementMapEffect(
                             SkDisplacementMapEffect::ChannelSelectorType xChannelSelector,
                             SkDisplacementMapEffect::ChannelSelectorType yChannelSelector,
                             const SkVector& scale,
                             GrTexture* displacement,
                             const SkMatrix& offsetMatrix,
                             GrTexture* color,
                             const SkISize& colorDimensions)
    : fDisplacementTransform(kLocal_GrCoordSet, offsetMatrix, displacement,
                             GrTextureParams::kNone_FilterMode)
    , fDisplacementAccess(displacement)
    , fColorTransform(kLocal_GrCoordSet, color, GrTextureParams::kNone_FilterMode)
    , fDomain(GrTextureDomain::MakeTexelDomain(color, SkIRect::MakeSize(colorDimensions)),
              GrTextureDomain::kDecal_Mode)
    , fColorAccess(color)
    , fXChannelSelector(xChannelSelector)
    , fYChannelSelector(yChannelSelector)
    , fScale(scale) {
    this->initClassID<GrDisplacementMapEffect>();
    this->addCoordTransform(&fDisplacementTransform);
    this->addTextureAccess(&fDisplacementAccess);
    this->addCoordTransform(&fColorTransform);
    this->addTextureAccess(&fColorAccess);
}

GrDisplacementMapEffect::~GrDisplacementMapEffect() {
}

bool GrDisplacementMapEffect::onIsEqual(const GrFragmentProcessor& sBase) const {
    const GrDisplacementMapEffect& s = sBase.cast<GrDisplacementMapEffect>();
    return fXChannelSelector == s.fXChannelSelector &&
           fYChannelSelector == s.fYChannelSelector &&
           fScale == s.fScale;
}

void GrDisplacementMapEffect::onComputeInvariantOutput(GrInvariantOutput* inout) const {
    // Any displacement offset bringing a pixel out of bounds will output a color of (0,0,0,0),
    // so the only way we'd get a constant alpha is if the input color image has a constant alpha
    // and no displacement offset push any texture coordinates out of bounds OR if the constant
    // alpha is 0. Since this isn't trivial to compute at this point, let's assume the output is
    // not of constant color when a displacement effect is applied.
    inout->setToUnknown(GrInvariantOutput::kWillNot_ReadInput);
}

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

GR_DEFINE_FRAGMENT_PROCESSOR_TEST(GrDisplacementMapEffect);

sk_sp<GrFragmentProcessor> GrDisplacementMapEffect::TestCreate(GrProcessorTestData* d) {
    int texIdxDispl = d->fRandom->nextBool() ? GrProcessorUnitTest::kSkiaPMTextureIdx :
                                               GrProcessorUnitTest::kAlphaTextureIdx;
    int texIdxColor = d->fRandom->nextBool() ? GrProcessorUnitTest::kSkiaPMTextureIdx :
                                               GrProcessorUnitTest::kAlphaTextureIdx;
    static const int kMaxComponent = 4;
    SkDisplacementMapEffect::ChannelSelectorType xChannelSelector =
        static_cast<SkDisplacementMapEffect::ChannelSelectorType>(
                d->fRandom->nextRangeU(1, kMaxComponent));
    SkDisplacementMapEffect::ChannelSelectorType yChannelSelector =
        static_cast<SkDisplacementMapEffect::ChannelSelectorType>(
                d->fRandom->nextRangeU(1, kMaxComponent));
    SkVector scale = SkVector::Make(d->fRandom->nextRangeScalar(0, 100.0f),
                                    d->fRandom->nextRangeScalar(0, 100.0f));
    SkISize colorDimensions;
    colorDimensions.fWidth = d->fRandom->nextRangeU(0, d->fTextures[texIdxColor]->width());
    colorDimensions.fHeight = d->fRandom->nextRangeU(0, d->fTextures[texIdxColor]->height());
    return GrDisplacementMapEffect::Make(xChannelSelector, yChannelSelector, scale,
                                         d->fTextures[texIdxDispl], SkMatrix::I(),
                                         d->fTextures[texIdxColor], colorDimensions);
}

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

void GrGLDisplacementMapEffect::emitCode(EmitArgs& args) {
    const GrDisplacementMapEffect& displacementMap = args.fFp.cast<GrDisplacementMapEffect>();
    const GrTextureDomain& domain = displacementMap.domain();

    fScaleUni = args.fUniformHandler->addUniform(kFragment_GrShaderFlag,
                                                 kVec2f_GrSLType, kDefault_GrSLPrecision, "Scale");
    const char* scaleUni = args.fUniformHandler->getUniformCStr(fScaleUni);
    const char* dColor = "dColor";
    const char* cCoords = "cCoords";
    const char* nearZero = "1e-6"; // Since 6.10352e−5 is the smallest half float, use
                                   // a number smaller than that to approximate 0, but
                                   // leave room for 32-bit float GPU rounding errors.

    GrGLSLFPFragmentBuilder* fragBuilder = args.fFragBuilder;
    fragBuilder->codeAppendf("\t\tvec4 %s = ", dColor);
    fragBuilder->appendTextureLookup(args.fTexSamplers[0], args.fCoords[0].c_str(),
                                   args.fCoords[0].getType());
    fragBuilder->codeAppend(";\n");

    // Unpremultiply the displacement
    fragBuilder->codeAppendf(
        "\t\t%s.rgb = (%s.a < %s) ? vec3(0.0) : clamp(%s.rgb / %s.a, 0.0, 1.0);",
        dColor, dColor, nearZero, dColor, dColor);
    SkString coords2D = fragBuilder->ensureFSCoords2D(args.fCoords, 1);
    fragBuilder->codeAppendf("\t\tvec2 %s = %s + %s*(%s.",
                             cCoords, coords2D.c_str(), scaleUni, dColor);

    switch (displacementMap.xChannelSelector()) {
      case SkDisplacementMapEffect::kR_ChannelSelectorType:
        fragBuilder->codeAppend("r");
        break;
      case SkDisplacementMapEffect::kG_ChannelSelectorType:
        fragBuilder->codeAppend("g");
        break;
      case SkDisplacementMapEffect::kB_ChannelSelectorType:
        fragBuilder->codeAppend("b");
        break;
      case SkDisplacementMapEffect::kA_ChannelSelectorType:
        fragBuilder->codeAppend("a");
        break;
      case SkDisplacementMapEffect::kUnknown_ChannelSelectorType:
      default:
        SkDEBUGFAIL("Unknown X channel selector");
    }

    switch (displacementMap.yChannelSelector()) {
      case SkDisplacementMapEffect::kR_ChannelSelectorType:
        fragBuilder->codeAppend("r");
        break;
      case SkDisplacementMapEffect::kG_ChannelSelectorType:
        fragBuilder->codeAppend("g");
        break;
      case SkDisplacementMapEffect::kB_ChannelSelectorType:
        fragBuilder->codeAppend("b");
        break;
      case SkDisplacementMapEffect::kA_ChannelSelectorType:
        fragBuilder->codeAppend("a");
        break;
      case SkDisplacementMapEffect::kUnknown_ChannelSelectorType:
      default:
        SkDEBUGFAIL("Unknown Y channel selector");
    }
    fragBuilder->codeAppend("-vec2(0.5));\t\t");

    fGLDomain.sampleTexture(fragBuilder,
                            args.fUniformHandler,
                            args.fGLSLCaps,
                            domain,
                            args.fOutputColor,
                            SkString(cCoords),
                            args.fTexSamplers[1]);
    fragBuilder->codeAppend(";\n");
}

void GrGLDisplacementMapEffect::onSetData(const GrGLSLProgramDataManager& pdman,
                                          const GrProcessor& proc) {
    const GrDisplacementMapEffect& displacementMap = proc.cast<GrDisplacementMapEffect>();
    GrTexture* colorTex = displacementMap.texture(1);
    SkScalar scaleX = displacementMap.scale().fX / colorTex->width();
    SkScalar scaleY = displacementMap.scale().fY / colorTex->height();
    pdman.set2f(fScaleUni, SkScalarToFloat(scaleX),
                colorTex->origin() == kTopLeft_GrSurfaceOrigin ?
                SkScalarToFloat(scaleY) : SkScalarToFloat(-scaleY));
    fGLDomain.setData(pdman, displacementMap.domain(), colorTex->origin());
}

void GrGLDisplacementMapEffect::GenKey(const GrProcessor& proc,
                                       const GrGLSLCaps&, GrProcessorKeyBuilder* b) {
    const GrDisplacementMapEffect& displacementMap = proc.cast<GrDisplacementMapEffect>();

    uint32_t xKey = displacementMap.xChannelSelector();
    uint32_t yKey = displacementMap.yChannelSelector() << kChannelSelectorKeyBits;

    b->add32(xKey | yKey);
}
#endif