如何在不预乘alpha的情况下获取真实的RGBA或ARGB颜色值？

// Execute premultiply logic on RGBA components split into componenets.
// For example, a pixel RGB (128, 0, 0) with A = 128
// would return (255, 0, 0) with A = 128

static
inline
uint32_t premultiply_bgra_inline(uint32_t red, uint32_t green, uint32_t blue, uint32_t alpha)
{
  const uint8_t* const restrict alphaTable = &extern_alphaTablesPtr[alpha * PREMULT_TABLEMAX];
  uint32_t result = (alpha << 24) | (alphaTable[red] << 16) | (alphaTable[green] << 8) | alphaTable[blue];
  return result;
}

static inline
int unpremultiply(const uint32_t premultRGBComponent, const float alphaMult, const uint32_t alpha)
{
  float multVal = premultRGBComponent * alphaMult;
  float floorVal = floor(multVal);
  uint32_t unpremultRGBComponent = (uint32_t)floorVal;
  assert(unpremultRGBComponent >= 0);
  if (unpremultRGBComponent > 255) {
    unpremultRGBComponent = 255;
  }

  // Pass the unpremultiplied estimated value through the
  // premultiply table again to verify that the result
  // maps back to the same rgb component value that was
  // passed in. It is possible that the result of the
  // multiplication is smaller or larger than the
  // original value, so this will either add or remove
  // one int value to the result rgb component to account
  // for the error possibility.

  uint32_t premultPixel = premultiply_bgra_inline(unpremultRGBComponent, 0, 0, alpha);

  uint32_t premultActualRGBComponent = (premultPixel >> 16) & 0xFF;

  if (premultRGBComponent != premultActualRGBComponent) {
    if ((premultActualRGBComponent < premultRGBComponent) && (unpremultRGBComponent < 255)) {
      unpremultRGBComponent += 1;
    } else if ((premultActualRGBComponent > premultRGBComponent) && (unpremultRGBComponent > 0)) {
      unpremultRGBComponent -= 1;
    } else {
      // This should never happen
      assert(0);
    }
  }

  return unpremultRGBComponent;
}