thanks for replies guys.
finaly i managed to plot a white circle (png sprite) on the c_trace hitted place. the thing now is, that this circle is alleays round. i want to stretch it in one axis according to the angle the beam hits the wall (to make it look more realistic). so now i have to get the angle with which the c_race is hitting the wall.
can someone give me an idea how to get this angle.

thanks in advance