Will share source code if someone is interested, but key bits:
- had a small JS glue layer using CanvasRenderingContext2D to render
- made a `wasm32-freestanding` build to lower the wasm bundle size, which meant shimming the bits of the libc microui uses
- constant repainting (while literally nothing changes) -> constant CPU load
- some libs can skip repaints but have no concept of damage area
- bad handling of high-dpi (which also can change dynamically)
- constant repainting behaves even worse on laptops which announce 180 Hz refresh interval, which means that it drains the battery 3 times faster than 60 Hz
This doesn't explain a 100% CPU usage since requestAnimationFrame is vsync-throttled and rendering such a simple scene will do the per-frame work in a fraction of a frame duration.
And FWIW I cannot reproduce the issue in both demos (in Chrome on macOS). The sokol demo has a per-frame load of about 0.3ms per 8.333ms frame, and the demo hosted on vercel.app about 0.7ms, both pretty much within expecations.