Under some circumstances, the driver may choose to return a temporary surface instead of a pointer to the original. Make sure to pass the actual view volume to be mapped to the transfer function rather than adjusting the map pointer after-the-fact. Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu> Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>