# wayland-bar-compositor

A Wayland compositor written in jolt directly on wlroots, for putting a Wayland
panel (such as `cosmic-panel`) onto an X11 desktop.

There is no shared object here: `jolt.ffi` binds libwlroots, libwayland-server,
libxkbcommon, libX11, libXext and libXi directly. The compositor opens one
wlroots X11 output, draws layer-shell and xdg-shell clients through the wlroots
scene graph, and forwards pointer and keyboard input to them.

Because it owns the scene, it shapes its own X11 window: the bar strip plus
the outline of whatever popups are mapped, traced from the rendered frame so
rounded corners show the desktop behind them. XInput2 raw button presses on the
root window let a click on an X11 app close open popups.

    wayland-bar-compositor   the compositor
    build                    generates offsets.edn from the installed headers
    gen-offsets.c            the offsetof dump build compiles
    offsets.edn              wlroots struct layout facts, read at startup
    protocol/                wlr-layer-shell XML for the header wlroots omits

## Running

```bash
./build     # after any wlroots update
WLR_BACKENDS=x11 WLR_RENDERER=pixman \
  ./wayland-bar-compositor --size 1920x640 --strip 0,0,1920,40 --title my-bar -- cosmic-panel
```

`--size` is the whole output, bar plus room for popups; `--strip` is the part
always shown; `--title` names the X11 window so a launcher can find it and dock
it (`_NET_WM_WINDOW_TYPE_DOCK` plus a strut). Set `WBC_DEBUG=1` to log input,
popups and shape changes.

## Why a compositor in jolt works

Every wlroots listener shares one native callback that dispatches on the
listener's address, and listeners come from a free list, so surfaces that come
and go don't leak callbacks. The event loop is `wl_event_loop_dispatch` called
from jolt's own thread, so every callback arrives on that thread — nothing
blocks the collector. wlroots changes struct layouts between minor versions,
which is why the offsets are generated from the headers rather than written by
hand.

Written for wlroots 0.20 on x86_64. On a native Wayland desktop — COSMIC with
cosmic-comp, for one — none of this is needed: the panel runs directly.