Most performant way to allow user to draw masks over image?

[anshap1719]

I'm building an image-editing app where I have a rectangular "canvas" of sort where I display the source image. I want the user to be able to draw a mask image over the source image, sort of like traditional masks in Photoshop or Lightroom or similar softwares.

Since the user will be drawing it, it's very important to keep the re-render times low enough for a 60fps render of the mask image on each update.

It doesn't matter if the source image buffer is manipulated directly, or we have a transparent area over the source image which is filled in based on a separate mask buffer. Both approaches are fine by me.

What would be my best option to achieve this? I initially thought that since SharedPixelBuffer is internally reference counted, updating it would automatically update the image that's using it, but that didn't seem to be the case.