C++ SkPixmap::addr8方法代码示例

// returns true and set color if the bitmap can be drawn as a single color
// (for efficiency)
static bool can_use_color_shader(const SkImage* image, SkColor* color) {
#ifdef SK_BUILD_FOR_ANDROID_FRAMEWORK
    // HWUI does not support color shaders (see b/22390304)
    return false;
#endif

    if (1 != image->width() || 1 != image->height()) {
        return false;
    }

    SkPixmap pmap;
    if (!image->peekPixels(&pmap)) {
        return false;
    }

    switch (pmap.colorType()) {
    case kN32_SkColorType:
        *color = SkUnPreMultiply::PMColorToColor(*pmap.addr32(0, 0));
        return true;
    case kRGB_565_SkColorType:
        *color = SkPixel16ToColor(*pmap.addr16(0, 0));
        return true;
    case kIndex_8_SkColorType: {
        const SkColorTable& ctable = *pmap.ctable();
        *color = SkUnPreMultiply::PMColorToColor(ctable[*pmap.addr8(0, 0)]);
        return true;
    }
    default: // just skip the other configs for now
        break;
    }
    return false;
}

static void pack4xHToLCD16(const SkPixmap& src, const SkMask& dst,
                           const SkMaskGamma::PreBlend& maskPreBlend) {
#define SAMPLES_PER_PIXEL 4
#define LCD_PER_PIXEL 3
    SkASSERT(kAlpha_8_SkColorType == src.colorType());
    SkASSERT(SkMask::kLCD16_Format == dst.fFormat);

    const int sample_width = src.width();
    const int height = src.height();

    uint16_t* dstP = (uint16_t*)dst.fImage;
    size_t dstRB = dst.fRowBytes;
    // An N tap FIR is defined by
    // out[n] = coeff[0]*x[n] + coeff[1]*x[n-1] + ... + coeff[N]*x[n-N]
    // or
    // out[n] = sum(i, 0, N, coeff[i]*x[n-i])

    // The strategy is to use one FIR (different coefficients) for each of r, g, and b.
    // This means using every 4th FIR output value of each FIR and discarding the rest.
    // The FIRs are aligned, and the coefficients reach 5 samples to each side of their 'center'.
    // (For r and b this is technically incorrect, but the coeffs outside round to zero anyway.)

    // These are in some fixed point repesentation.
    // Adding up to more than one simulates ink spread.
    // For implementation reasons, these should never add up to more than two.

    // Coefficients determined by a gausian where 5 samples = 3 std deviations (0x110 'contrast').
    // Calculated using tools/generate_fir_coeff.py
    // With this one almost no fringing is ever seen, but it is imperceptibly blurry.
    // The lcd smoothed text is almost imperceptibly different from gray,
    // but is still sharper on small stems and small rounded corners than gray.
    // This also seems to be about as wide as one can get and only have a three pixel kernel.
    // TODO: caculate these at runtime so parameters can be adjusted (esp contrast).
    static const unsigned int coefficients[LCD_PER_PIXEL][SAMPLES_PER_PIXEL*3] = {
        //The red subpixel is centered inside the first sample (at 1/6 pixel), and is shifted.
        { 0x03, 0x0b, 0x1c, 0x33,  0x40, 0x39, 0x24, 0x10,  0x05, 0x01, 0x00, 0x00, },
        //The green subpixel is centered between two samples (at 1/2 pixel), so is symetric
        { 0x00, 0x02, 0x08, 0x16,  0x2b, 0x3d, 0x3d, 0x2b,  0x16, 0x08, 0x02, 0x00, },
        //The blue subpixel is centered inside the last sample (at 5/6 pixel), and is shifted.
        { 0x00, 0x00, 0x01, 0x05,  0x10, 0x24, 0x39, 0x40,  0x33, 0x1c, 0x0b, 0x03, },
    };

    for (int y = 0; y < height; ++y) {
        const uint8_t* srcP = src.addr8(0, y);

        // TODO: this fir filter implementation is straight forward, but slow.
        // It should be possible to make it much faster.
        for (int sample_x = -4, pixel_x = 0; sample_x < sample_width + 4; sample_x += 4, ++pixel_x) {
            int fir[LCD_PER_PIXEL] = { 0 };
            for (int sample_index = SkMax32(0, sample_x - 4), coeff_index = sample_index - (sample_x - 4)
                ; sample_index < SkMin32(sample_x + 8, sample_width)
                ; ++sample_index, ++coeff_index)
            {
                int sample_value = srcP[sample_index];
                for (int subpxl_index = 0; subpxl_index < LCD_PER_PIXEL; ++subpxl_index) {
                    fir[subpxl_index] += coefficients[subpxl_index][coeff_index] * sample_value;
                }
            }
            for (int subpxl_index = 0; subpxl_index < LCD_PER_PIXEL; ++subpxl_index) {
                fir[subpxl_index] /= 0x100;
                fir[subpxl_index] = SkMin32(fir[subpxl_index], 255);
            }

            U8CPU r = sk_apply_lut_if<APPLY_PREBLEND>(fir[0], maskPreBlend.fR);
            U8CPU g = sk_apply_lut_if<APPLY_PREBLEND>(fir[1], maskPreBlend.fG);
            U8CPU b = sk_apply_lut_if<APPLY_PREBLEND>(fir[2], maskPreBlend.fB);
#if SK_SHOW_TEXT_BLIT_COVERAGE
            r = SkMax32(r, 10); g = SkMax32(g, 10); b = SkMax32(b, 10);
#endif
            dstP[pixel_x] = SkPack888ToRGB16(r, g, b);
        }
        dstP = (uint16_t*)((char*)dstP + dstRB);
    }
}