WARNING: Cushy is in early alpha. This guide doubly so.
Canvas
The Canvas widget invokes a function each time it needs to paint.
This function has access to a graphics context exposing most of
Kludine's 2D graphics API.
A Tick can be attached to the Canvas to have a callback invoked at a
steady rate. This tick function can be used to update the state of the Canvas,
and it can signal when the Canvas should be redrawn.