Building the test canvas (250,000 strokes + a zoom chain 10^48 deep)…

Mouse: left-drag draw · wheel zoom · right/middle-drag pan · A auto-zoom · H home · D draw mode
Touch/pen: pan mode — 1 finger pans, double-tap auto-zoom · draw mode — 1 finger/pen draws · pinch zooms in both
URL options: ?mass=1000000 · ?chain=25 (start deep)