/** Updates a rectangular region of a face. Storage must be defined
beforehand. The image data must be in a format mathing the defined storage
and the update region must be fully inside the face. */
void sub_image(TextureCubeFace face, unsigned level, int x, int y, unsigned w, unsigned h, const void *data);
/** Updates a rectangular region of a face. Storage must be defined
beforehand. The image data must be in a format mathing the defined storage
and the update region must be fully inside the face. */
void sub_image(TextureCubeFace face, unsigned level, int x, int y, unsigned w, unsigned h, const void *data);