/** Updates a cuboid-shaped region of the texture. Storage must be defined
and allocated beforehand. The update region must be fully inside the
texture. */
void sub_image(unsigned level,
int x, int y, int z, unsigned wd, unsigned ht, unsigned dp,
/** Updates a cuboid-shaped region of the texture. Storage must be defined
and allocated beforehand. The update region must be fully inside the
texture. */
void sub_image(unsigned level,
int x, int y, int z, unsigned wd, unsigned ht, unsigned dp,