pub type PFN_glTexSubImage3DOES = unsafe extern "system" fn(_target: GLenum, _level: GLint, _xoffset: GLint, _yoffset: GLint, _zoffset: GLint, _width: GLsizei, _height: GLsizei, _depth: GLsizei, _format: GLenum, _type: GLenum, _pixels: *const c_void);