When the canvas is set to accept clicks, it will create a closed selection specified by the mouse clicks, you can then move, delete or add "Control Points".
You can extract the selection to use in whatever you need, you can also use the included "Region" class to detect clicks on a given selection and so on.
Selection Canvas is licensed and distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3.0 License.
