RGBA alpha-blending

static inline void blend32(uint32 *dstPixel, uint32 color)
{
    uint8 *dst = (uint8*) dstPixel;
    uint8 r = (color & 0xFF000000) >> 24;
    uint8 g = (color & 0x00FF0000) >> 16;
    uint8 b = (color & 0x0000FF00) >> 8;
    uint8 a = color & 0x000000FF;

    if (a == 255) {
        // direct copy
        dst[0] = b;
        dst[1] = g;
        dst[2] = r;
        dst[3] = a;
    }
    else if (a == 0) {
        // do not copy
    }
    else {
        // alpha-blending
        // http://en.wikipedia.org/wiki/Alpha_compositing
        uint8 bo = dst[0];
        uint8 go = dst[1];
        uint8 ro = dst[2];
        uint8 ao = dst[3];
        uint8 aof = (ao * (255 - a)) >> 8;
        dst[3] = a + aof;
        dst[0] = (b * a + bo * aof) / dst[3];
        dst[1] = (g * a + go * aof) / dst[3];
        dst[2] = (r * a + ro * aof) / dst[3];
    }
}