Extending PencilKit APIs even further

Extending the PencilKit APIs to expose the inner data structures was a great move! And for apps like the "Handwriting Tutor" sample app this is enough.

However, I'd love to implement a custom drawing engine based on PKDrawing since it provides a lot of functionality out of the box (user interaction through PKCanvasView, de-/serialization, spline interpolation). But for a custom renderer, two key parts are missing:

• Custom inks (FB8261616), so we can define custom brushes that render differently than the three system styles.

• Detecting changes while the user is drawing (FB8261554), otherwise we can't draw their current stroke on screen.

I know this was mentioned here before, but I wanted to emphasize that those two features would enable us to implement a full custom render engine based on PencilKit.

Thanks for considering!