Refraction through a Prism
1. Drag the yellow cross to translate the prism.
2. When the item "Changeable" is selected, the shape of the prism can be changed by left-dragging any one of its three corners.
3. Rotate the prism about the yellow cross by right-dragging (or control-dragging) any one of its three corners.
4. Click the position of a particular refraction/reflection, the values of the angles will be shown. Click other places to remove the marking.