A Moving Line Explained

To add a line connecting the two moving points we just need to add one equation that defines the line based on the points we want to anchor it. Here I’ve written out the equation in terms of P and Q, and parameterized the same way as the static lines in the animation. The only difference is that the anchor points are defined as moving points instead of still ones.

Does it matter which point we use as the “start” of the line? Try switching out the variables in the equation of the moving line and see for yourself!