src/core/SkConfig8888.cpp

/*
 * Copyright 2014 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "SkBitmap.h"
#include "SkCanvas.h"
#include "SkConfig8888.h"
#include "SkColorPriv.h"
#include "SkDither.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;
}

static void rect_memcpy(void* dst, size_t dstRB, const void* src, size_t srcRB, size_t bytesPerRow,
                        int rowCount) {
    SkASSERT(bytesPerRow <= srcRB);
    SkASSERT(bytesPerRow <= dstRB);
    for (int i = 0; i < rowCount; ++i) {
        memcpy(dst, src, bytesPerRow);
        dst = (char*)dst + dstRB;
        src = (const char*)src + srcRB;
    }
}

bool SkPixelInfo::CopyPixels(const SkImageInfo& dstInfo, void* dstPixels, size_t dstRB,
                             const SkImageInfo& srcInfo, const void* srcPixels, size_t srcRB,
                             SkColorTable* ctable) {
    if (srcInfo.dimensions() != dstInfo.dimensions()) {
        return false;
    }

    const int width = srcInfo.width();
    const int height = srcInfo.height();

    // Handle fancy alpha swizzling if both are ARGB32
    if (4 == srcInfo.bytesPerPixel() && 4 == dstInfo.bytesPerPixel()) {
        SkDstPixelInfo dstPI;
        dstPI.fColorType = dstInfo.colorType();
        dstPI.fAlphaType = dstInfo.alphaType();
        dstPI.fPixels = dstPixels;
        dstPI.fRowBytes = dstRB;
        
        SkSrcPixelInfo srcPI;
        srcPI.fColorType = srcInfo.colorType();
        srcPI.fAlphaType = srcInfo.alphaType();
        srcPI.fPixels = srcPixels;
        srcPI.fRowBytes = srcRB;
        
        return srcPI.convertPixelsTo(&dstPI, width, height);
    }

    // If they agree on colorType and the alphaTypes are compatible, then we just memcpy.
    // Note: we've already taken care of 32bit colortypes above.
    if (srcInfo.colorType() == dstInfo.colorType()) {
        switch (srcInfo.colorType()) {
            case kRGB_565_SkColorType:
            case kAlpha_8_SkColorType:
                break;
            case kIndex_8_SkColorType:
            case kARGB_4444_SkColorType:
                if (srcInfo.alphaType() != dstInfo.alphaType()) {
                    return false;
                }
                break;
            default:
                return false;
        }
        rect_memcpy(dstPixels, dstRB, srcPixels, srcRB, width * srcInfo.bytesPerPixel(), height);
        return true;
    }

    /*
     *  Begin section where we try to change colorTypes along the way. Not all combinations
     *  are supported.
     */

    // Can no longer draw directly into 4444, but we can manually whack it for a few combinations
    if (kARGB_4444_SkColorType == dstInfo.colorType() &&
        (kN32_SkColorType == srcInfo.colorType() || kIndex_8_SkColorType == srcInfo.colorType())) {
        if (srcInfo.alphaType() == kUnpremul_SkAlphaType) {
            // Our method for converting to 4444 assumes premultiplied.
            return false;
        }
        
        const SkPMColor* table = NULL;
        if (kIndex_8_SkColorType == srcInfo.colorType()) {
            if (NULL == ctable) {
                return false;
            }
            table = ctable->lockColors();
        }

        for (int y = 0; y < height; ++y) {
            DITHER_4444_SCAN(y);
            SkPMColor16* SK_RESTRICT dstRow = (SkPMColor16*)dstPixels;
            if (table) {
                const uint8_t* SK_RESTRICT srcRow = (const uint8_t*)srcPixels;
                for (int x = 0; x < width; ++x) {
                    dstRow[x] = SkDitherARGB32To4444(table[srcRow[x]], DITHER_VALUE(x));
                }
            } else {
                const SkPMColor* SK_RESTRICT srcRow = (const SkPMColor*)srcPixels;
                for (int x = 0; x < width; ++x) {
                    dstRow[x] = SkDitherARGB32To4444(srcRow[x], DITHER_VALUE(x));
                }
            }
            dstPixels = (char*)dstPixels + dstRB;
            srcPixels = (const char*)srcPixels + srcRB;
        }
        
        if (table) {
            ctable->unlockColors();
        }
        return true;
    }

    if (dstInfo.alphaType() == kUnpremul_SkAlphaType) {
        // We do not support drawing to unpremultiplied bitmaps.
        return false;
    }

    // Final fall-back, draw with a canvas
    //
    // Always clear the dest in case one of the blitters accesses it
    // TODO: switch the allocation of tmpDst to call sk_calloc_throw
    {
        SkBitmap bm;
        if (!bm.installPixels(srcInfo, const_cast<void*>(srcPixels), srcRB, ctable, NULL, NULL)) {
            return false;
        }
        SkAutoTUnref<SkCanvas> canvas(SkCanvas::NewRasterDirect(dstInfo, dstPixels, dstRB));
        if (NULL == canvas.get()) {
            return false;
        }

        SkPaint  paint;
        paint.setDither(true);

        canvas->clear(0);
        canvas->drawBitmap(bm, 0, 0, &paint);
        return true;
    }
}