BGD_DECLARE(void) gdImageColorTransparent (gdImagePtr im, int color)
{
  if (!im->trueColor)
    {
      if (im->transparent != -1)
	{
	  im->alpha[im->transparent] = gdAlphaOpaque;
	}
      if (color != -1)
	{
	  im->alpha[color] = gdAlphaTransparent;
	}
    }
  im->transparent = color;
}
Unknown