`fireOnEveryPaint` seems… hacky

[jakearchibald]

It seems hacky to have an option to ResizeObserver that actually makes it a paint invalidation observer. Feels like there should be a particular observer for this, eg PaintInvalidationObserver. Paint invalidation would also happen on resize, so usage should be simple.

[StephenHaney]

I apologize if this is unrelated, but there is a need for an browser API to run user code after layout but before paint.

If you're drawing to canvas and need to keep your drawing frame-synced with DOM changes, you need to measure DOM positions after layout but before paint, and then do your canvas draw calls (which are safe and won't invalidate layout). A real example is drawing selection highlights over top of DOM elements in a design tool.

You can currently hack it by triggering a ResizeObserver every frame to get a callback with the correct timing (repo example here)

I wanted to share this in case it's more support for your suggestion. If this is too unrelated just let me know and I'll hide the post.