Is your feature request related to a problem? Please describe.
There are plenty of places where I would like to use a Context but have to get a reference to it from the Ui, when it's perfectly feasible to allow Ui to deref into a Context.

Describe the solution you'd like
Implement Deref for Ui to point to the painter context that the ctx() method points to.

Describe alternatives you've considered
Implementing an external trait to forward all method calls on Ui to Context.