Request for comments: Customizable image based watchface

I have actually removed all possibilities for image resources but uncompressed binary, since the other types are not really beneficial for anything. That shaves another couple of percent of the draw time.
I had not seen setClipRect yet, that could be really useful to draw partially, without having to split the background in several parts. Splitting the background would be possible for native watchfaces, but for the automatic amazfit conversion probably not that easy since there are no bounds to image sizes.
Is it correct, that I could set a ClipRect and then just drawImage with the full screen size background and have it only touch the ClipRect pixels and be faster than drawing without ClipRect? That would be an awesome alternative to drawing into Arraybuffers and compositing them together.