Warning: This function is
currently not documented; only the argument list is
available.
Warning: This function is
EXPERIMENTAL. The behaviour of this function, the
name of this function, and anything else documented about this
function may change without notice in a future release of PHP.
Use this function at your own risk.
Sets the opacity to use when drawing using the fill color or fill texture. Fully opaque is 1.0.
Return Values
No value is returned.