This is neat, some years ago i also thought of making a simple DPaint clone (though much simpler than what this project seems to do) and started by... painting the tool icons, then losing interest :-P. I did end up reusing them for a pixelart editing component for Lazarus though[0] (and put the icons in my "Bad-Common-Icons" icon set[1] that i use for my GUI programs). But i do want to, at some point, tackle making something like Paint Shop Pro 7 (for desktop, not web) because i think it has the best UX of all image editing programs (including later versions of PSP which i never liked).

That said, i played with this a bit and found some bug with the smudge tool blending[2]. It also seems browser-related as it has different behavior in Firefox and Falkon (which uses QtWebEngine / Chromium). Also the way opacity works with the smudge tool feels weird/wrong as even at 1% it seems to affect the image a lot even though it should barely make a difference.

[0] https://i.imgur.com/kht16dJ.png

[1] http://runtimeterror.com/tools/icons/

[2] https://github.com/steffest/DPaint-js/issues/50