# Schcom — the Schunix Compositor

Owns the display. Every pixel that reaches the screen goes through it.

Clients do not draw to the framebuffer; they draw into their own buffers and
hand them over. Schcom decides what is on top of what, composites the result,
and presents it. It also owns input: it reads the raw event devices and sends
each event to whichever client should have it.

That is the whole job. Window *placement* is not part of it — that is SchWM's,
and Schcom exposes a protocol for it rather than implementing policy itself.

## Status

Not started. Scoped only.

## What it needs from the kernel first

| Need | State |
|---|---|
| Shared memory (`shmget`/`shmat`/`shmdt`) | done |
| `mmap` of `/dev/fb0` | done |
| Framebuffer geometry via the fbdev ioctls | done |
| **Unix domain sockets**, with `SCM_RIGHTS` | **missing** — `socket()` is a `NO_LINUX` stub |
| **Raw input events** — key down/up with modifiers | **missing** — input only arrives cooked, through the tty line discipline |
| Mode setting and double buffering | **missing** — needs the virtio-gpu driver |

The two marked missing are hard blockers, not inconveniences. A client and
the compositor have to pass a buffer handle between them, and a pipe cannot
carry one. And a compositor that reads the tty gets line-buffered text
delivered to a single foreground process, which is not input in any sense it
can use.

## Design notes, so far

- **Buffers are shared memory, not pipes.** A pipe means copying every frame;
  at 800×600×32 that is 1.9 MB per frame per client. shm exists for this.
- **One protocol, versioned from the start.** SchWM and SchDE are separate
  programs, so the protocol is a real compatibility surface from day one, not
  after the fact.
- **Policy belongs to SchWM.** If Schcom starts deciding where windows go, the
  split has already failed.