Request for comments: Customizable image based watchface

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?

Yes... although it may not be as much faster as you expect so I'd test. While offscreen bitmaps generally get ignored, Espruino may still end up going through every pixel and just not drawing it for some images