code: func Frustum(left float64, right float64, bottom float64, top float64, zNear float64, zFar float64) {
  	syscall.Syscall6(gpFrustum, 6, uintptr(math.Float64bits(left)), uintptr(math.Float64bits(right)), uintptr(math.Float64bits(bottom)), uintptr(math.Float64bits(top)), uintptr(math.Float64bits(zNear)), uintptr(math.Float64bits(zFar)))
  }
docs: // multiply the current matrix by a perspective matrix