src/core/SkConfig8888.cpp

#include "SkConfig8888.h"
#include "SkColorPriv.h"
#include "SkMathPriv.h"
#include "SkUnPreMultiply.h"

enum AlphaVerb {
    kNothing_AlphaVerb,
    kPremul_AlphaVerb,
    kUnpremul_AlphaVerb,
};

template <bool doSwapRB, AlphaVerb doAlpha> uint32_t convert32(uint32_t c) {
    if (doSwapRB) {
        c = SkSwizzle_RB(c);
    }

    // Lucky for us, in both RGBA and BGRA, the alpha component is always in the same place, so
    // we can perform premul or unpremul the same way without knowing the swizzles for RGB.
    switch (doAlpha) {
        case kNothing_AlphaVerb:
            // no change
            break;
        case kPremul_AlphaVerb:
            c = SkPreMultiplyARGB(SkGetPackedA32(c), SkGetPackedR32(c),
                                  SkGetPackedG32(c), SkGetPackedB32(c));
            break;
        case kUnpremul_AlphaVerb:
            c = SkUnPreMultiply::UnPreMultiplyPreservingByteOrder(c);
            break;
    }
    return c;
}

template <bool doSwapRB, AlphaVerb doAlpha>
void convert32_row(uint32_t* dst, const uint32_t* src, int count) {
    // This has to be correct if src == dst (but not partial overlap)
    for (int i = 0; i < count; ++i) {
        dst[i] = convert32<doSwapRB, doAlpha>(src[i]);
    }
}

static bool is_32bit_colortype(SkColorType ct) {
    return kRGBA_8888_SkColorType == ct || kBGRA_8888_SkColorType == ct;
}

static AlphaVerb compute_AlphaVerb(SkAlphaType src, SkAlphaType dst) {
    SkASSERT(kIgnore_SkAlphaType != src);
    SkASSERT(kIgnore_SkAlphaType != dst);

    if (kOpaque_SkAlphaType == src || kOpaque_SkAlphaType == dst || src == dst) {
        return kNothing_AlphaVerb;
    }
    if (kPremul_SkAlphaType == dst) {
        SkASSERT(kUnpremul_SkAlphaType == src);
        return kPremul_AlphaVerb;
    } else {
        SkASSERT(kPremul_SkAlphaType == src);
        SkASSERT(kUnpremul_SkAlphaType == dst);
        return kUnpremul_AlphaVerb;
    }
}

static void memcpy32_row(uint32_t* dst, const uint32_t* src, int count) {
    memcpy(dst, src, count * 4);
}

bool SkSrcPixelInfo::convertPixelsTo(SkDstPixelInfo* dst, int width, int height) const {
    if (width <= 0 || height <= 0) {
        return false;
    }

    if (!is_32bit_colortype(fColorType) || !is_32bit_colortype(dst->fColorType)) {
        return false;
    }

    void (*proc)(uint32_t* dst, const uint32_t* src, int count);
    AlphaVerb doAlpha = compute_AlphaVerb(fAlphaType, dst->fAlphaType);
    bool doSwapRB = fColorType != dst->fColorType;

    switch (doAlpha) {
        case kNothing_AlphaVerb:
            if (doSwapRB) {
                proc = convert32_row<true, kNothing_AlphaVerb>;
            } else {
                if (fPixels == dst->fPixels) {
                    return true;
                }
                proc = memcpy32_row;
            }
            break;
        case kPremul_AlphaVerb:
            if (doSwapRB) {
                proc = convert32_row<true, kPremul_AlphaVerb>;
            } else {
                proc = convert32_row<false, kPremul_AlphaVerb>;
            }
            break;
        case kUnpremul_AlphaVerb:
            if (doSwapRB) {
                proc = convert32_row<true, kUnpremul_AlphaVerb>;
            } else {
                proc = convert32_row<false, kUnpremul_AlphaVerb>;
            }
            break;
    }

    uint32_t* dstP = static_cast<uint32_t*>(dst->fPixels);
    const uint32_t* srcP = static_cast<const uint32_t*>(fPixels);
    size_t srcInc = fRowBytes >> 2;
    size_t dstInc = dst->fRowBytes >> 2;
    for (int y = 0; y < height; ++y) {
        proc(dstP, srcP, width);
        dstP += dstInc;
        srcP += srcInc;
    }
    return true;
}