src/effects/SkTableMaskFilter.cpp

/*
 * Copyright 2011 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "include/core/SkString.h"
#include "include/effects/SkTableMaskFilter.h"
#include "include/private/SkFixed.h"
#include "include/private/SkTPin.h"
#include "src/core/SkReadBuffer.h"
#include "src/core/SkWriteBuffer.h"

class SkTableMaskFilterImpl : public SkMaskFilterBase {
public:
    explicit SkTableMaskFilterImpl(const uint8_t table[256]);

    SkMask::Format getFormat() const override;
    bool filterMask(SkMask*, const SkMask&, const SkMatrix&, SkIPoint*) const override;

protected:
    ~SkTableMaskFilterImpl() override;

    void flatten(SkWriteBuffer&) const override;

private:
    SK_FLATTENABLE_HOOKS(SkTableMaskFilterImpl)

    SkTableMaskFilterImpl();

    uint8_t fTable[256];

    using INHERITED = SkMaskFilter;
};

SkTableMaskFilterImpl::SkTableMaskFilterImpl() {
    for (int i = 0; i < 256; i++) {
        fTable[i] = i;
    }
}

SkTableMaskFilterImpl::SkTableMaskFilterImpl(const uint8_t table[256]) {
    memcpy(fTable, table, sizeof(fTable));
}

SkTableMaskFilterImpl::~SkTableMaskFilterImpl() {}

bool SkTableMaskFilterImpl::filterMask(SkMask* dst, const SkMask& src,
                                 const SkMatrix&, SkIPoint* margin) const {
    if (src.fFormat != SkMask::kA8_Format) {
        return false;
    }

    dst->fBounds = src.fBounds;
    dst->fRowBytes = SkAlign4(dst->fBounds.width());
    dst->fFormat = SkMask::kA8_Format;
    dst->fImage = nullptr;

    if (src.fImage) {
        dst->fImage = SkMask::AllocImage(dst->computeImageSize());

        const uint8_t* srcP = src.fImage;
        uint8_t* dstP = dst->fImage;
        const uint8_t* table = fTable;
        int dstWidth = dst->fBounds.width();
        int extraZeros = dst->fRowBytes - dstWidth;

        for (int y = dst->fBounds.height() - 1; y >= 0; --y) {
            for (int x = dstWidth - 1; x >= 0; --x) {
                dstP[x] = table[srcP[x]];
            }
            srcP += src.fRowBytes;
            // we can't just inc dstP by rowbytes, because if it has any
            // padding between its width and its rowbytes, we need to zero those
            // so that the bitters can read those safely if that is faster for
            // them
            dstP += dstWidth;
            for (int i = extraZeros - 1; i >= 0; --i) {
                *dstP++ = 0;
            }
        }
    }

    if (margin) {
        margin->set(0, 0);
    }
    return true;
}

SkMask::Format SkTableMaskFilterImpl::getFormat() const {
    return SkMask::kA8_Format;
}

void SkTableMaskFilterImpl::flatten(SkWriteBuffer& wb) const {
    wb.writeByteArray(fTable, 256);
}

sk_sp<SkFlattenable> SkTableMaskFilterImpl::CreateProc(SkReadBuffer& buffer) {
    uint8_t table[256];
    if (!buffer.readByteArray(table, 256)) {
        return nullptr;
    }
    return sk_sp<SkFlattenable>(SkTableMaskFilter::Create(table));
}

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

SkMaskFilter* SkTableMaskFilter::Create(const uint8_t table[256]) {
    return new SkTableMaskFilterImpl(table);
}

SkMaskFilter* SkTableMaskFilter::CreateGamma(SkScalar gamma) {
    uint8_t table[256];
    MakeGammaTable(table, gamma);
    return new SkTableMaskFilterImpl(table);
}

SkMaskFilter* SkTableMaskFilter::CreateClip(uint8_t min, uint8_t max) {
    uint8_t table[256];
    MakeClipTable(table, min, max);
    return new SkTableMaskFilterImpl(table);
}

void SkTableMaskFilter::MakeGammaTable(uint8_t table[256], SkScalar gamma) {
    const float dx = 1 / 255.0f;
    const float g = SkScalarToFloat(gamma);

    float x = 0;
    for (int i = 0; i < 256; i++) {
     // float ee = powf(x, g) * 255;
        table[i] = SkTPin(sk_float_round2int(powf(x, g) * 255), 0, 255);
        x += dx;
    }
}

void SkTableMaskFilter::MakeClipTable(uint8_t table[256], uint8_t min,
                                      uint8_t max) {
    if (0 == max) {
        max = 1;
    }
    if (min >= max) {
        min = max - 1;
    }
    SkASSERT(min < max);

    SkFixed scale = (1 << 16) * 255 / (max - min);
    memset(table, 0, min + 1);
    for (int i = min + 1; i < max; i++) {
        int value = SkFixedRoundToInt(scale * (i - min));
        SkASSERT(value <= 255);
        table[i] = value;
    }
    memset(table + max, 255, 256 - max);

#if 0
    int j;
    for (j = 0; j < 256; j++) {
        if (table[j]) {
            break;
        }
    }
    SkDebugf("%d %d start [%d]", min, max, j);
    for (; j < 256; j++) {
        SkDebugf(" %d", table[j]);
    }
    SkDebugf("\n\n");
#endif
}