Steiner symmetrization
For each vertical line, the shape’s slice is moved so its midpoint lies on the horizontal axis. Its slice lengths—and therefore its area—stay unchanged, while the form becomes more balanced about that axis.
How to use it
Place at least three points, then close the shape. Rotate it before applying the operation to choose a different direction. Repeating a small turn and symmetrization gives a sense of how the shape settles.
Keys: Enter close · S apply · A/D turn · F repeat · C clear
Open problem
Can every polygon be turned into a convex polygon by finitely many Steiner symmetrizations?