src/effects/gradients/SkRadialGradient.cpp

/*
 * Copyright 2012 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "SkRadialGradient.h"
#include "SkRadialGradient_Table.h"
#include "SkNx.h"

#define kSQRT_TABLE_BITS    11
#define kSQRT_TABLE_SIZE    (1 << kSQRT_TABLE_BITS)

static_assert(sizeof(gSqrt8Table) == kSQRT_TABLE_SIZE, "SqrtTableSizesMatch");

#if 0

#include <stdio.h>

void SkRadialGradient_BuildTable() {
    // build it 0..127 x 0..127, so we use 2^15 - 1 in the numerator for our "fixed" table

    FILE* file = ::fopen("SkRadialGradient_Table.h", "w");
    SkASSERT(file);
    ::fprintf(file, "static const uint8_t gSqrt8Table[] = {\n");

    for (int i = 0; i < kSQRT_TABLE_SIZE; i++) {
        if ((i & 15) == 0) {
            ::fprintf(file, "\t");
        }

        uint8_t value = SkToU8(SkFixedSqrt(i * SK_Fixed1 / kSQRT_TABLE_SIZE) >> 8);

        ::fprintf(file, "0x%02X", value);
        if (i < kSQRT_TABLE_SIZE-1) {
            ::fprintf(file, ", ");
        }
        if ((i & 15) == 15) {
            ::fprintf(file, "\n");
        }
    }
    ::fprintf(file, "};\n");
    ::fclose(file);
}

#endif

namespace {

// GCC doesn't like using static functions as template arguments.  So force these to be non-static.
inline SkFixed mirror_tileproc_nonstatic(SkFixed x) {
    return mirror_tileproc(x);
}

inline SkFixed repeat_tileproc_nonstatic(SkFixed x) {
    return repeat_tileproc(x);
}

SkMatrix rad_to_unit_matrix(const SkPoint& center, SkScalar radius) {
    SkScalar    inv = SkScalarInvert(radius);

    SkMatrix matrix;
    matrix.setTranslate(-center.fX, -center.fY);
    matrix.postScale(inv, inv);
    return matrix;
}

typedef void (* RadialShade16Proc)(SkScalar sfx, SkScalar sdx,
        SkScalar sfy, SkScalar sdy,
        uint16_t* dstC, const uint16_t* cache,
        int toggle, int count);

void shadeSpan16_radial_clamp(SkScalar sfx, SkScalar sdx,
        SkScalar sfy, SkScalar sdy,
        uint16_t* SK_RESTRICT dstC, const uint16_t* SK_RESTRICT cache,
        int toggle, int count) {
    const uint8_t* SK_RESTRICT sqrt_table = gSqrt8Table;

    /* knock these down so we can pin against +- 0x7FFF, which is an
       immediate load, rather than 0xFFFF which is slower. This is a
       compromise, since it reduces our precision, but that appears
       to be visually OK. If we decide this is OK for all of our cases,
       we could (it seems) put this scale-down into fDstToIndex,
       to avoid having to do these extra shifts each time.
    */
    SkFixed fx = SkScalarToFixed(sfx) >> 1;
    SkFixed dx = SkScalarToFixed(sdx) >> 1;
    SkFixed fy = SkScalarToFixed(sfy) >> 1;
    SkFixed dy = SkScalarToFixed(sdy) >> 1;
    // might perform this check for the other modes,
    // but the win will be a smaller % of the total
    if (dy == 0) {
        fy = SkTPin(fy, -0xFFFF >> 1, 0xFFFF >> 1);
        fy *= fy;
        do {
            unsigned xx = SkTPin(fx, -0xFFFF >> 1, 0xFFFF >> 1);
            unsigned fi = (xx * xx + fy) >> (14 + 16 - kSQRT_TABLE_BITS);
            fi = SkFastMin32(fi, 0xFFFF >> (16 - kSQRT_TABLE_BITS));
            fx += dx;
            *dstC++ = cache[toggle +
                            (sqrt_table[fi] >> SkGradientShaderBase::kSqrt16Shift)];
            toggle = next_dither_toggle16(toggle);
        } while (--count != 0);
    } else {
        do {
            unsigned xx = SkTPin(fx, -0xFFFF >> 1, 0xFFFF >> 1);
            unsigned fi = SkTPin(fy, -0xFFFF >> 1, 0xFFFF >> 1);
            fi = (xx * xx + fi * fi) >> (14 + 16 - kSQRT_TABLE_BITS);
            fi = SkFastMin32(fi, 0xFFFF >> (16 - kSQRT_TABLE_BITS));
            fx += dx;
            fy += dy;
            *dstC++ = cache[toggle +
                            (sqrt_table[fi] >> SkGradientShaderBase::kSqrt16Shift)];
            toggle = next_dither_toggle16(toggle);
        } while (--count != 0);
    }
}

template <SkFixed (*TileProc)(SkFixed)>
void shadeSpan16_radial(SkScalar fx, SkScalar dx, SkScalar fy, SkScalar dy,
                        uint16_t* SK_RESTRICT dstC, const uint16_t* SK_RESTRICT cache,
                        int toggle, int count) {
    do {
        const SkFixed dist = SkFloatToFixed(sk_float_sqrt(fx*fx + fy*fy));
        const unsigned fi = TileProc(dist);
        SkASSERT(fi <= 0xFFFF);
        *dstC++ = cache[toggle + (fi >> SkGradientShaderBase::kCache16Shift)];
        toggle = next_dither_toggle16(toggle);
        fx += dx;
        fy += dy;
    } while (--count != 0);
}

void shadeSpan16_radial_mirror(SkScalar fx, SkScalar dx, SkScalar fy, SkScalar dy,
                               uint16_t* SK_RESTRICT dstC, const uint16_t* SK_RESTRICT cache,
                               int toggle, int count) {
    shadeSpan16_radial<mirror_tileproc_nonstatic>(fx, dx, fy, dy, dstC, cache, toggle, count);
}

void shadeSpan16_radial_repeat(SkScalar fx, SkScalar dx, SkScalar fy, SkScalar dy,
                               uint16_t* SK_RESTRICT dstC, const uint16_t* SK_RESTRICT cache,
                               int toggle, int count) {
    shadeSpan16_radial<repeat_tileproc_nonstatic>(fx, dx, fy, dy, dstC, cache, toggle, count);
}

}  // namespace

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

SkRadialGradient::SkRadialGradient(const SkPoint& center, SkScalar radius, const Descriptor& desc)
    : SkGradientShaderBase(desc, rad_to_unit_matrix(center, radius))
    , fCenter(center)
    , fRadius(radius) {
}

size_t SkRadialGradient::contextSize() const {
    return sizeof(RadialGradientContext);
}

SkShader::Context* SkRadialGradient::onCreateContext(const ContextRec& rec, void* storage) const {
    return new (storage) RadialGradientContext(*this, rec);
}

SkRadialGradient::RadialGradientContext::RadialGradientContext(
        const SkRadialGradient& shader, const ContextRec& rec)
    : INHERITED(shader, rec) {}

void SkRadialGradient::RadialGradientContext::shadeSpan16(int x, int y, uint16_t* dstCParam,
                                                          int count) {
    SkASSERT(count > 0);

    const SkRadialGradient& radialGradient = static_cast<const SkRadialGradient&>(fShader);

    uint16_t* SK_RESTRICT dstC = dstCParam;

    SkPoint             srcPt;
    SkMatrix::MapXYProc dstProc = fDstToIndexProc;
    TileProc            proc = radialGradient.fTileProc;
    const uint16_t* SK_RESTRICT cache = fCache->getCache16();
    int                 toggle = init_dither_toggle16(x, y);

    if (fDstToIndexClass != kPerspective_MatrixClass) {
        dstProc(fDstToIndex, SkIntToScalar(x) + SK_ScalarHalf,
                             SkIntToScalar(y) + SK_ScalarHalf, &srcPt);

        SkScalar sdx = fDstToIndex.getScaleX();
        SkScalar sdy = fDstToIndex.getSkewY();

        if (fDstToIndexClass == kFixedStepInX_MatrixClass) {
            SkFixed storage[2];
            (void)fDstToIndex.fixedStepInX(SkIntToScalar(y),
                                           &storage[0], &storage[1]);
            sdx = SkFixedToScalar(storage[0]);
            sdy = SkFixedToScalar(storage[1]);
        } else {
            SkASSERT(fDstToIndexClass == kLinear_MatrixClass);
        }

        RadialShade16Proc shadeProc = shadeSpan16_radial_repeat;
        if (SkShader::kClamp_TileMode == radialGradient.fTileMode) {
            shadeProc = shadeSpan16_radial_clamp;
        } else if (SkShader::kMirror_TileMode == radialGradient.fTileMode) {
            shadeProc = shadeSpan16_radial_mirror;
        } else {
            SkASSERT(SkShader::kRepeat_TileMode == radialGradient.fTileMode);
        }
        (*shadeProc)(srcPt.fX, sdx, srcPt.fY, sdy, dstC,
                     cache, toggle, count);
    } else {    // perspective case
        SkScalar dstX = SkIntToScalar(x);
        SkScalar dstY = SkIntToScalar(y);
        do {
            dstProc(fDstToIndex, dstX, dstY, &srcPt);
            unsigned fi = proc(SkScalarToFixed(srcPt.length()));
            SkASSERT(fi <= 0xFFFF);

            int index = fi >> (16 - kCache16Bits);
            *dstC++ = cache[toggle + index];
            toggle = next_dither_toggle16(toggle);

            dstX += SK_Scalar1;
        } while (--count != 0);
    }
}

SkShader::GradientType SkRadialGradient::asAGradient(GradientInfo* info) const {
    if (info) {
        commonAsAGradient(info);
        info->fPoint[0] = fCenter;
        info->fRadius[0] = fRadius;
    }
    return kRadial_GradientType;
}

SkFlattenable* SkRadialGradient::CreateProc(SkReadBuffer& buffer) {
    DescriptorScope desc;
    if (!desc.unflatten(buffer)) {
        return nullptr;
    }
    const SkPoint center = buffer.readPoint();
    const SkScalar radius = buffer.readScalar();
    return SkGradientShader::CreateRadial(center, radius, desc.fColors, desc.fPos, desc.fCount,
                                          desc.fTileMode, desc.fGradFlags, desc.fLocalMatrix);
}

void SkRadialGradient::flatten(SkWriteBuffer& buffer) const {
    this->INHERITED::flatten(buffer);
    buffer.writePoint(fCenter);
    buffer.writeScalar(fRadius);
}

namespace {

inline bool radial_completely_pinned(SkScalar fx, SkScalar dx, SkScalar fy, SkScalar dy) {
    // fast, overly-conservative test: checks unit square instead of unit circle
    bool xClamped = (fx >= 1 && dx >= 0) || (fx <= -1 && dx <= 0);
    bool yClamped = (fy >= 1 && dy >= 0) || (fy <= -1 && dy <= 0);
    return xClamped || yClamped;
}

typedef void (* RadialShadeProc)(SkScalar sfx, SkScalar sdx,
        SkScalar sfy, SkScalar sdy,
        SkPMColor* dstC, const SkPMColor* cache,
        int count, int toggle);

static inline Sk4f fast_sqrt(const Sk4f& R) {
    // R * R.rsqrt0() is much faster, but it's non-monotonic, which isn't so pretty for gradients.
    return R * R.rsqrt1();
}

static inline Sk4f sum_squares(const Sk4f& a, const Sk4f& b) {
    return a * a + b * b;
}

void shadeSpan_radial_clamp2(SkScalar sfx, SkScalar sdx, SkScalar sfy, SkScalar sdy,
                             SkPMColor* SK_RESTRICT dstC, const SkPMColor* SK_RESTRICT cache,
                             int count, int toggle) {
    if (radial_completely_pinned(sfx, sdx, sfy, sdy)) {
        unsigned fi = SkGradientShaderBase::kCache32Count - 1;
        sk_memset32_dither(dstC,
                           cache[toggle + fi],
                           cache[next_dither_toggle(toggle) + fi],
                           count);
    } else {
        const Sk4f max(255);
        const float scale = 255;
        sfx *= scale;
        sfy *= scale;
        sdx *= scale;
        sdy *= scale;
        const Sk4f fx4(sfx, sfx + sdx, sfx + 2*sdx, sfx + 3*sdx);
        const Sk4f fy4(sfy, sfy + sdy, sfy + 2*sdy, sfy + 3*sdy);
        const Sk4f dx4(sdx * 4);
        const Sk4f dy4(sdy * 4);

        Sk4f tmpxy = fx4 * dx4 + fy4 * dy4;
        Sk4f tmpdxdy = sum_squares(dx4, dy4);
        Sk4f R = sum_squares(fx4, fy4);
        Sk4f dR = tmpxy + tmpxy + tmpdxdy;
        const Sk4f ddR = tmpdxdy + tmpdxdy;

        for (int i = 0; i < (count >> 2); ++i) {
            Sk4f dist = Sk4f::Min(fast_sqrt(R), max);
            R = R + dR;
            dR = dR + ddR;

            uint8_t fi[4];
            dist.toBytes(fi);

            for (int i = 0; i < 4; i++) {
                *dstC++ = cache[toggle + fi[i]];
                toggle = next_dither_toggle(toggle);
            }
        }
        count &= 3;
        if (count) {
            Sk4f dist = Sk4f::Min(fast_sqrt(R), max);

            uint8_t fi[4];
            dist.toBytes(fi);
            for (int i = 0; i < count; i++) {
                *dstC++ = cache[toggle + fi[i]];
                toggle = next_dither_toggle(toggle);
            }
        }
    }
}

// Unrolling this loop doesn't seem to help (when float); we're stalling to
// get the results of the sqrt (?), and don't have enough extra registers to
// have many in flight.
template <SkFixed (*TileProc)(SkFixed)>
void shadeSpan_radial(SkScalar fx, SkScalar dx, SkScalar fy, SkScalar dy,
                      SkPMColor* SK_RESTRICT dstC, const SkPMColor* SK_RESTRICT cache,
                      int count, int toggle) {
    do {
        const SkFixed dist = SkFloatToFixed(sk_float_sqrt(fx*fx + fy*fy));
        const unsigned fi = TileProc(dist);
        SkASSERT(fi <= 0xFFFF);
        *dstC++ = cache[toggle + (fi >> SkGradientShaderBase::kCache32Shift)];
        toggle = next_dither_toggle(toggle);
        fx += dx;
        fy += dy;
    } while (--count != 0);
}

void shadeSpan_radial_mirror(SkScalar fx, SkScalar dx, SkScalar fy, SkScalar dy,
                             SkPMColor* SK_RESTRICT dstC, const SkPMColor* SK_RESTRICT cache,
                             int count, int toggle) {
    shadeSpan_radial<mirror_tileproc_nonstatic>(fx, dx, fy, dy, dstC, cache, count, toggle);
}

void shadeSpan_radial_repeat(SkScalar fx, SkScalar dx, SkScalar fy, SkScalar dy,
                             SkPMColor* SK_RESTRICT dstC, const SkPMColor* SK_RESTRICT cache,
                             int count, int toggle) {
    shadeSpan_radial<repeat_tileproc_nonstatic>(fx, dx, fy, dy, dstC, cache, count, toggle);
}

}  // namespace

void SkRadialGradient::RadialGradientContext::shadeSpan(int x, int y,
                                                        SkPMColor* SK_RESTRICT dstC, int count) {
    SkASSERT(count > 0);

    const SkRadialGradient& radialGradient = static_cast<const SkRadialGradient&>(fShader);

    SkPoint             srcPt;
    SkMatrix::MapXYProc dstProc = fDstToIndexProc;
    TileProc            proc = radialGradient.fTileProc;
    const SkPMColor* SK_RESTRICT cache = fCache->getCache32();
    int toggle = init_dither_toggle(x, y);

    if (fDstToIndexClass != kPerspective_MatrixClass) {
        dstProc(fDstToIndex, SkIntToScalar(x) + SK_ScalarHalf,
                             SkIntToScalar(y) + SK_ScalarHalf, &srcPt);
        SkScalar sdx = fDstToIndex.getScaleX();
        SkScalar sdy = fDstToIndex.getSkewY();

        if (fDstToIndexClass == kFixedStepInX_MatrixClass) {
            SkFixed storage[2];
            (void)fDstToIndex.fixedStepInX(SkIntToScalar(y),
                                           &storage[0], &storage[1]);
            sdx = SkFixedToScalar(storage[0]);
            sdy = SkFixedToScalar(storage[1]);
        } else {
            SkASSERT(fDstToIndexClass == kLinear_MatrixClass);
        }

        RadialShadeProc shadeProc = shadeSpan_radial_repeat;
        if (SkShader::kClamp_TileMode == radialGradient.fTileMode) {
            shadeProc = shadeSpan_radial_clamp2;
        } else if (SkShader::kMirror_TileMode == radialGradient.fTileMode) {
            shadeProc = shadeSpan_radial_mirror;
        } else {
            SkASSERT(SkShader::kRepeat_TileMode == radialGradient.fTileMode);
        }
        (*shadeProc)(srcPt.fX, sdx, srcPt.fY, sdy, dstC, cache, count, toggle);
    } else {    // perspective case
        SkScalar dstX = SkIntToScalar(x);
        SkScalar dstY = SkIntToScalar(y);
        do {
            dstProc(fDstToIndex, dstX, dstY, &srcPt);
            unsigned fi = proc(SkScalarToFixed(srcPt.length()));
            SkASSERT(fi <= 0xFFFF);
            *dstC++ = cache[fi >> SkGradientShaderBase::kCache32Shift];
            dstX += SK_Scalar1;
        } while (--count != 0);
    }
}

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

#if SK_SUPPORT_GPU

#include "SkGr.h"
#include "glsl/GrGLSLCaps.h"
#include "glsl/GrGLSLFragmentShaderBuilder.h"

class GrGLRadialGradient : public GrGLGradientEffect {
public:

    GrGLRadialGradient(const GrProcessor&) {}
    virtual ~GrGLRadialGradient() { }

    virtual void emitCode(EmitArgs&) override;

    static void GenKey(const GrProcessor& processor, const GrGLSLCaps&, GrProcessorKeyBuilder* b) {
        b->add32(GenBaseGradientKey(processor));
    }

private:

    typedef GrGLGradientEffect INHERITED;

};

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

class GrRadialGradient : public GrGradientEffect {
public:
    static GrFragmentProcessor* Create(GrContext* ctx,
                                       const SkRadialGradient& shader,
                                       const SkMatrix& matrix,
                                       SkShader::TileMode tm) {
        return new GrRadialGradient(ctx, shader, matrix, tm);
    }

    virtual ~GrRadialGradient() { }

    const char* name() const override { return "Radial Gradient"; }

private:
    GrRadialGradient(GrContext* ctx,
                     const SkRadialGradient& shader,
                     const SkMatrix& matrix,
                     SkShader::TileMode tm)
        : INHERITED(ctx, shader, matrix, tm) {
        this->initClassID<GrRadialGradient>();
    }

    GrGLSLFragmentProcessor* onCreateGLSLInstance() const override {
        return new GrGLRadialGradient(*this);
    }

    virtual void onGetGLSLProcessorKey(const GrGLSLCaps& caps,
                                       GrProcessorKeyBuilder* b) const override {
        GrGLRadialGradient::GenKey(*this, caps, b);
    }

    GR_DECLARE_FRAGMENT_PROCESSOR_TEST;

    typedef GrGradientEffect INHERITED;
};

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

GR_DEFINE_FRAGMENT_PROCESSOR_TEST(GrRadialGradient);

const GrFragmentProcessor* GrRadialGradient::TestCreate(GrProcessorTestData* d) {
    SkPoint center = {d->fRandom->nextUScalar1(), d->fRandom->nextUScalar1()};
    SkScalar radius = d->fRandom->nextUScalar1();

    SkColor colors[kMaxRandomGradientColors];
    SkScalar stopsArray[kMaxRandomGradientColors];
    SkScalar* stops = stopsArray;
    SkShader::TileMode tm;
    int colorCount = RandomGradientParams(d->fRandom, colors, &stops, &tm);
    SkAutoTUnref<SkShader> shader(SkGradientShader::CreateRadial(center, radius,
                                                                 colors, stops, colorCount,
                                                                 tm));
    const GrFragmentProcessor* fp = shader->asFragmentProcessor(d->fContext,
        GrTest::TestMatrix(d->fRandom), NULL, kNone_SkFilterQuality);
    GrAlwaysAssert(fp);
    return fp;
}

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

void GrGLRadialGradient::emitCode(EmitArgs& args) {
    const GrRadialGradient& ge = args.fFp.cast<GrRadialGradient>();
    this->emitUniforms(args.fUniformHandler, ge);
    SkString t("length(");
    t.append(args.fFragBuilder->ensureFSCoords2D(args.fCoords, 0));
    t.append(")");
    this->emitColor(args.fFragBuilder,
                    args.fUniformHandler,
                    args.fGLSLCaps,
                    ge, t.c_str(),
                    args.fOutputColor,
                    args.fInputColor,
                    args.fSamplers);
}

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

const GrFragmentProcessor* SkRadialGradient::asFragmentProcessor(
                                                 GrContext* context,
                                                 const SkMatrix& viewM,
                                                 const SkMatrix* localMatrix,
                                                 SkFilterQuality) const {
    SkASSERT(context);

    SkMatrix matrix;
    if (!this->getLocalMatrix().invert(&matrix)) {
        return nullptr;
    }
    if (localMatrix) {
        SkMatrix inv;
        if (!localMatrix->invert(&inv)) {
            return nullptr;
        }
        matrix.postConcat(inv);
    }
    matrix.postConcat(fPtsToUnit);
        SkAutoTUnref<const GrFragmentProcessor> inner(
            GrRadialGradient::Create(context, *this, matrix, fTileMode));
    return GrFragmentProcessor::MulOutputByInputAlpha(inner);
}

#endif

#ifndef SK_IGNORE_TO_STRING
void SkRadialGradient::toString(SkString* str) const {
    str->append("SkRadialGradient: (");

    str->append("center: (");
    str->appendScalar(fCenter.fX);
    str->append(", ");
    str->appendScalar(fCenter.fY);
    str->append(") radius: ");
    str->appendScalar(fRadius);
    str->append(" ");

    this->INHERITED::toString(str);

    str->append(")");
}
#endif