But what, you might ask, have these shadows to do with triangles? To answer this, we have to do something sneaky.
We'll take the shadow on the ground and move it up until it touches the bottom of the stick. We’ll take the shadow on the wall and move it until it touches the top of the stick. Drag the stick and see the result:
Surprise! We have a triangle, with a base corresponding to the ground shadow and a height corresponding to the wall shadow. Notice that these lines always form a right angle, no matter where the stick is.
Real World Alert! Remember the question about why real shadows don’t work the way the shadows in this program do? See the difference here.