x1 reflects/mirrors/echoes x2 [object/radiation] to observer/point x3 as x4; x2 bounces on x1.
Also: x1 is a mirror/reflector. x2 may be light, lu'e of an imaged object; x4 may be image or echo or the same as x2 if physical object; x3 may be a path for a bounced object; ka is reflection. See also catlu, viska, lenjo, pensi.