# pi_slint_frontend

Builds and installs `slint-frontend/` from the app repo - the native front-end that
exists because the React UI is sluggish on the kiosk. Installed *alongside* the web UI,
never instead of it, and the systemd unit is installed but not enabled: the device still
boots into the kiosk browser.

```sh
systemctl start musikdelfin     # takes over the screen
systemctl stop  musikdelfin     # back to the browser underneath
```

or over SSH, `DISPLAY=:0 /usr/local/bin/musikdelfin`.

## Why this builds on the device

`pi_musicmouse` builds the web front-end on the control machine and rsyncs `dist/`,
because npm output is portable and npm is not installed on the Pis. A Rust binary is
not portable, so this role has a harder choice.

The Pis run **32-bit armhf Raspbian on a 64-bit kernel** - `uname -m` says `aarch64`
and `dpkg --print-architecture` says `armhf`, and the second one is the one that
matters. The target is `armv7-unknown-linux-gnueabihf`. Cross-compiling to it from the
control machine needs a sysroot, and the devices carry no `-dev` packages to build one
out of, so it would have to be reconstructed from the Debian archive - and then kept in
step with the devices' glibc forever. Spending the device's own CPU once is the smaller
liability. A rebuild only happens when the commit changes.

The same fact rules out the Skia renderer: rust-skia publishes no prebuilt binaries for
armhf, so `--features kiosk` would mean compiling Skia from source on a Pi. This role
builds `--features desktop` - winit, FemtoVG and the software renderer - and runs as an
X client in the existing session rather than taking over KMS.

`SLINT_BACKEND=winit-software musikdelfin` switches renderer without a rebuild, which
is the thing to try first if the GPU path misbehaves. The FemtoVG bug that makes
`kiosk` use Skia upstream (slint-ui/slint#11785) was reported on a Pi 5 with a 64-bit
userland, so it may well not apply here - but it is worth checking that album covers
actually appear before drawing conclusions about frame rate.

## First run

Roughly 40 minutes: 570 crates on two cores. Later runs are incremental and usually
seconds. The build is `nice`d and limited to two jobs, which bounds peak memory on
musicdolphin's 1.8 GB.