eah I think the default scene use too much samples, like 51 for the right light.

Now my technique of combining shadow samples together is probably not the most efficient, I draw them with source-over and an alpha which is also a wrong hacky current implementation... but maybe using the CanvasData would be less efficient (technically I need to make the average of shadow samples' grayscales) - well we never know, I haven't tried yet ;)

I would be happy to have any contribution in the library :)

the editor could turn down samples for lights while dragging, and turn samples back up when dragging is finished.