eta/Post uses two light sources directed from the specific locations to the model.  This function allows the user to rotate the light sources along the screen X and Y axes. The function only works when the SHADE option is turned on.  The program displays the locations of the light source 1 and 2 and their lighting directions when the function starts. The user uses the mouse to move the light sources on the screen. The lighting effect is updated as the user moves the mouse. The user may activate this function by pressing the SHIFT – CTRL keys and LEFT mouse button simultaneously. Release SHIFT – CTRL keys and move the mouse to rotate light source. Release the mouse button to exit the function.