Interactive: Ellipse drawing

[plegner]

An interactive component for the Conic Sections course, that allows students to draw an ellipse using a virtual pencil and a rope that is connected to two pegs (the foci of the ellipse):

Students should be able to move the pencil as well as the position of the two foci, by clicking and dragging with finger or mouse.

The rope needs some basic physics simulation (rope/chain) to model behaviour when it is slack. The pencil should be movable to anywhere within the ellipse, not just the positions along the edge, and leave a faint trail of where it has been.

[plegner]

Here is a simple draft that connects the three points in a triangle:
https://github.com/mathigon/textbooks/blob/ellipse/content/circles/components/ellipse.ts

But we want a more realistic "physics" version like this: