The React UI is sluggish on the kiosk and the reasons are browser-shaped: a compositor
deciding what gets its own layer, a requestAnimationFrame loop repainting the viewport,
and a JPEG decode per album card per cold start. The last three commits chased that
through the service worker and the cover pipeline. This is the other direction - the
same backend, the same layout, the same German copy, without a browser.
Browse and play only. The typing game, the room-lights page, parent mode and the
IR-remote assignment stay web-only, and nothing here touches python-backend.
Four things carry the performance claim, in rough order of how much they should matter:
Covers are downscaled once, ever. The backend serves one size - 640px on the long edge,
no ?size= - and a grid card is 180. src/covers.rs fetches each cover once on a worker
thread, resizes it, and writes a JPEG thumbnail to ~/.cache/musicmouse-slint/covers/.
Two tiers and only two, which is what makes the cache worth keeping: a per-widget pixel
size would give each album a dozen near-identical files and a fresh decode for each. The
cache is dropped when the websocket announces a rescan, because that is the one moment
the backend rewrites the art behind an unchanged cover URL - the trap sw.js had to learn
about the hard way.
The grid is virtualized. Rust hands the UI the album list pre-chunked into rows and the
view puts those in a ListView, which instantiates only what is on screen. A flat list of
660 cards gives it no rows to skip, hence the chunking. Same purpose as
content-visibility: auto on .grid > .card.
The progress bar animates between the 2 Hz pushes rather than running a clock, so
interpolation costs a property evaluation per frame on the render side and there is no
equivalent of usePlaybackClock. It is suppressed for the frame a track changes on, so a
new track jumps instead of sliding across two unrelated positions.
Nothing on screen animates by itself. The ambient canvas is not ported, for the reason
lib/lowPower.ts already gives: a loop repainting the viewport is a floor you cannot get
under while it runs at all.
The device must not use FemtoVG. On Mesa V3D it draws every runtime-loaded Image as
solid black (slint-ui/slint#11785, open), which here means every album cover; Skia and
the software renderer are unaffected. So `kiosk` is linuxkms + Skia and FemtoVG stays
the default only for desktop development. Both profiles are verified to build; the kiosk
binary links libinput/libgbm/libdrm and no X11 or Wayland at all.
lib/search.ts, lib/keyboard.ts and lib/format.ts were already pure functions with their
own tests, so they port across as pure Rust with theirs: 43 tests, no window required.
The .slint files are layout only - nothing in them formats a number or picks a word.
Verified against the real 660-album library rather than a fixture. tools/headless-shots.sh
renders the UI inside a nested headless compositor and grabs a frame per screen, which
is how that was checked on a machine whose session was locked; a Slint window needs a
real compositor, and under bare Xvfb nothing maps at all.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
