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"

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

#if defined(SK_BUILD_FOR_WIN32) && defined(SK_DEBUG)

#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 {

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

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

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 = SkPin32(fy, -0xFFFF >> 1, 0xFFFF >> 1);
        fy *= fy;
        do {
            unsigned xx = SkPin32(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 ^= SkGradientShaderBase::kDitherStride16;
        } while (--count != 0);
    } else {
        do {
            unsigned xx = SkPin32(fx, -0xFFFF >> 1, 0xFFFF >> 1);
            unsigned fi = SkPin32(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 ^= SkGradientShaderBase::kDitherStride16;
        } while (--count != 0);
    }
}

void shadeSpan16_radial_mirror(SkScalar sfx, SkScalar sdx,
        SkScalar sfy, SkScalar sdy,
        uint16_t* SK_RESTRICT dstC, const uint16_t* SK_RESTRICT cache,
        int toggle, int count) {
    do {
#ifdef SK_SCALAR_IS_FLOAT
        float fdist = sk_float_sqrt(sfx*sfx + sfy*sfy);
        SkFixed dist = SkFloatToFixed(fdist);
#else
        SkFixed magnitudeSquared = SkFixedSquare(sfx) +
            SkFixedSquare(sfy);
        if (magnitudeSquared < 0) // Overflow.
            magnitudeSquared = SK_FixedMax;
        SkFixed dist = SkFixedSqrt(magnitudeSquared);
#endif
        unsigned fi = mirror_tileproc(dist);
        SkASSERT(fi <= 0xFFFF);
        *dstC++ = cache[toggle + (fi >> SkGradientShaderBase::kCache16Shift)];
        toggle ^= SkGradientShaderBase::kDitherStride16;
        sfx += sdx;
        sfy += sdy;
    } while (--count != 0);
}

void shadeSpan16_radial_repeat(SkScalar sfx, SkScalar sdx,
        SkScalar sfy, SkScalar sdy,
        uint16_t* SK_RESTRICT dstC, const uint16_t* SK_RESTRICT cache,
        int toggle, int count) {
    SkFixed fx = SkScalarToFixed(sfx);
    SkFixed dx = SkScalarToFixed(sdx);
    SkFixed fy = SkScalarToFixed(sfy);
    SkFixed dy = SkScalarToFixed(sdy);
    do {
        SkFixed dist = SkFixedSqrt(SkFixedSquare(fx) + SkFixedSquare(fy));
        unsigned fi = repeat_tileproc(dist);
        SkASSERT(fi <= 0xFFFF);
        fx += dx;
        fy += dy;
        *dstC++ = cache[toggle + (fi >> SkGradientShaderBase::kCache16Shift)];
        toggle ^= SkGradientShaderBase::kDitherStride16;
    } while (--count != 0);
}

}

SkRadialGradient::SkRadialGradient(const SkPoint& center, SkScalar radius,
                const SkColor colors[], const SkScalar pos[], int colorCount,
                SkShader::TileMode mode, SkUnitMapper* mapper)
    : SkGradientShaderBase(colors, pos, colorCount, mode, mapper),
      fCenter(center),
      fRadius(radius)
{
    // make sure our table is insync with our current #define for kSQRT_TABLE_SIZE
    SkASSERT(sizeof(gSqrt8Table) == kSQRT_TABLE_SIZE);

    rad_to_unit_matrix(center, radius, &fPtsToUnit);
}

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

    uint16_t* SK_RESTRICT dstC = dstCParam;

    SkPoint             srcPt;
    SkMatrix::MapXYProc dstProc = fDstToIndexProc;
    TileProc            proc = fTileProc;
    const uint16_t* SK_RESTRICT cache = this->getCache16();
    int                 toggle = ((x ^ y) & 1) * kDitherStride16;

    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 == fTileMode) {
            shadeProc = shadeSpan16_radial_clamp;
        } else if (SkShader::kMirror_TileMode == fTileMode) {
            shadeProc = shadeSpan16_radial_mirror;
        } else {
            SkASSERT(SkShader::kRepeat_TileMode == 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 ^= kDitherStride16;

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

SkShader::BitmapType SkRadialGradient::asABitmap(SkBitmap* bitmap, 
    SkMatrix* matrix, SkShader::TileMode* xy) const {
    if (bitmap) {
        this->commonAsABitmap(bitmap);
    }
    if (matrix) {
        matrix->setScale(SkIntToScalar(kGradient32Length),
                         SkIntToScalar(kGradient32Length));
        matrix->preConcat(fPtsToUnit);
    }
    if (xy) {
        xy[0] = fTileMode;
        xy[1] = kClamp_TileMode;
    }
    return kRadial_BitmapType;
}

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

GrCustomStage* SkRadialGradient::asNewCustomStage(GrContext* context,
    GrSamplerState* sampler) const {
    SkASSERT(NULL != context && NULL != sampler);
    sampler->matrix()->preConcat(fPtsToUnit);
    sampler->textureParams()->setTileModeX(fTileMode);
    sampler->textureParams()->setTileModeY(kClamp_TileMode);
    sampler->textureParams()->setBilerp(true);
    return SkNEW_ARGS(GrRadialGradient, (context, *this, sampler));
}

SkRadialGradient::SkRadialGradient(SkFlattenableReadBuffer& buffer)
    : INHERITED(buffer),
      fCenter(buffer.readPoint()),
      fRadius(buffer.readScalar()) {
}

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

namespace {

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

    return xClamped || yClamped;
}

// Return true if (fx * fy) is always inside the unit circle
// SkPin32 is expensive, but so are all the SkFixedMul in this test,
// so it shouldn't be run if count is small.
inline bool no_need_for_radial_pin(int fx, int dx,
                                          int fy, int dy, int count) {
    SkASSERT(count > 0);
    if (SkAbs32(fx) > 0x7FFF || SkAbs32(fy) > 0x7FFF) {
        return false;
    }
    if (fx*fx + fy*fy > 0x7FFF*0x7FFF) {
        return false;
    }
    fx += (count - 1) * dx;
    fy += (count - 1) * dy;
    if (SkAbs32(fx) > 0x7FFF || SkAbs32(fy) > 0x7FFF) {
        return false;
    }
    return fx*fx + fy*fy <= 0x7FFF*0x7FFF;
}

#define UNPINNED_RADIAL_STEP \
    fi = (fx * fx + fy * fy) >> (14 + 16 - kSQRT_TABLE_BITS); \
    *dstC++ = cache[toggle + \
                    (sqrt_table[fi] >> SkGradientShaderBase::kSqrt32Shift)]; \
    toggle ^= SkGradientShaderBase::kDitherStride32; \
    fx += dx; \
    fy += dy;

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

// On Linux, this is faster with SkPMColor[] params than SkPMColor* SK_RESTRICT
void shadeSpan_radial_clamp(SkScalar sfx, SkScalar sdx,
        SkScalar sfy, SkScalar sdy,
        SkPMColor* SK_RESTRICT dstC, const SkPMColor* SK_RESTRICT cache,
        int count, int toggle) {
    // Floating point seems to be slower than fixed point,
    // even when we have float hardware.
    const uint8_t* SK_RESTRICT sqrt_table = gSqrt8Table;
    SkFixed fx = SkScalarToFixed(sfx) >> 1;
    SkFixed dx = SkScalarToFixed(sdx) >> 1;
    SkFixed fy = SkScalarToFixed(sfy) >> 1;
    SkFixed dy = SkScalarToFixed(sdy) >> 1;
    if ((count > 4) && radial_completely_pinned(fx, dx, fy, dy)) {
        unsigned fi = SkGradientShaderBase::kGradient32Length;
        sk_memset32_dither(dstC,
            cache[toggle + fi],
            cache[(toggle ^ SkGradientShaderBase::kDitherStride32) + fi],
            count);
    } else if ((count > 4) &&
               no_need_for_radial_pin(fx, dx, fy, dy, count)) {
        unsigned fi;
        // 4x unroll appears to be no faster than 2x unroll on Linux
        while (count > 1) {
            UNPINNED_RADIAL_STEP;
            UNPINNED_RADIAL_STEP;
            count -= 2;
        }
        if (count) {
            UNPINNED_RADIAL_STEP;
        }
    }
    else  {
        // Specializing for dy == 0 gains us 25% on Skia benchmarks
        if (dy == 0) {
            unsigned yy = SkPin32(fy, -0xFFFF >> 1, 0xFFFF >> 1);
            yy *= yy;
            do {
                unsigned xx = SkPin32(fx, -0xFFFF >> 1, 0xFFFF >> 1);
                unsigned fi = (xx * xx + yy) >> (14 + 16 - kSQRT_TABLE_BITS);
                fi = SkFastMin32(fi, 0xFFFF >> (16 - kSQRT_TABLE_BITS));
                *dstC++ = cache[toggle + (sqrt_table[fi] >>
                    SkGradientShaderBase::kSqrt32Shift)];
                toggle ^= SkGradientShaderBase::kDitherStride32;
                fx += dx;
            } while (--count != 0);
        } else {
            do {
                unsigned xx = SkPin32(fx, -0xFFFF >> 1, 0xFFFF >> 1);
                unsigned fi = SkPin32(fy, -0xFFFF >> 1, 0xFFFF >> 1);
                fi = (xx * xx + fi * fi) >> (14 + 16 - kSQRT_TABLE_BITS);
                fi = SkFastMin32(fi, 0xFFFF >> (16 - kSQRT_TABLE_BITS));
                *dstC++ = cache[toggle + (sqrt_table[fi] >>
                    SkGradientShaderBase::kSqrt32Shift)];
                toggle ^= SkGradientShaderBase::kDitherStride32;
                fx += dx;
                fy += dy;
            } while (--count != 0);
        }
    }
}

// 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.
void shadeSpan_radial_mirror(SkScalar sfx, SkScalar sdx,
        SkScalar sfy, SkScalar sdy,
        SkPMColor* SK_RESTRICT dstC, const SkPMColor* SK_RESTRICT cache,
        int count, int toggle) {
    do {
#ifdef SK_SCALAR_IS_FLOAT
        float fdist = sk_float_sqrt(sfx*sfx + sfy*sfy);
        SkFixed dist = SkFloatToFixed(fdist);
#else
        SkFixed magnitudeSquared = SkFixedSquare(sfx) +
            SkFixedSquare(sfy);
        if (magnitudeSquared < 0) // Overflow.
            magnitudeSquared = SK_FixedMax;
        SkFixed dist = SkFixedSqrt(magnitudeSquared);
#endif
        unsigned fi = mirror_tileproc(dist);
        SkASSERT(fi <= 0xFFFF);
        *dstC++ = cache[toggle + (fi >> SkGradientShaderBase::kCache32Shift)];
        toggle ^= SkGradientShaderBase::kDitherStride32;
        sfx += sdx;
        sfy += sdy;
    } while (--count != 0);
}

void shadeSpan_radial_repeat(SkScalar sfx, SkScalar sdx,
        SkScalar sfy, SkScalar sdy,
        SkPMColor* SK_RESTRICT dstC, const SkPMColor* SK_RESTRICT cache,
        int count, int toggle) {
    SkFixed fx = SkScalarToFixed(sfx);
    SkFixed dx = SkScalarToFixed(sdx);
    SkFixed fy = SkScalarToFixed(sfy);
    SkFixed dy = SkScalarToFixed(sdy);
    do {
        SkFixed magnitudeSquared = SkFixedSquare(fx) +
            SkFixedSquare(fy);
        if (magnitudeSquared < 0) // Overflow.
            magnitudeSquared = SK_FixedMax;
        SkFixed dist = SkFixedSqrt(magnitudeSquared);
        unsigned fi = repeat_tileproc(dist);
        SkASSERT(fi <= 0xFFFF);
        *dstC++ = cache[toggle + (fi >> SkGradientShaderBase::kCache32Shift)];
        toggle ^= SkGradientShaderBase::kDitherStride32;
        fx += dx;
        fy += dy;
    } while (--count != 0);
}
}

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

    SkPoint             srcPt;
    SkMatrix::MapXYProc dstProc = fDstToIndexProc;
    TileProc            proc = fTileProc;
    const SkPMColor* SK_RESTRICT cache = this->getCache32();
#ifdef USE_DITHER_32BIT_GRADIENT
    int toggle = ((x ^ y) & 1) * SkGradientShaderBase::kDitherStride32;
#else
    int toggle = 0;
#endif

    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 == fTileMode) {
            shadeProc = shadeSpan_radial_clamp;
        } else if (SkShader::kMirror_TileMode == fTileMode) {
            shadeProc = shadeSpan_radial_mirror;
        } else {
            SkASSERT(SkShader::kRepeat_TileMode == 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);
    }
}