| Filename | Latest commit message | Latest commit date |
|---|---|---|
8b7b8df74f
Groundwork for usb-tablet, which is the fix for the guest cursor and the
host's never being in the same place: a PS/2 mouse reports how far it
moved, two pointers accumulating deltas independently drift apart, and no
amount of care in the compositor can make them agree. An absolute device
reports where it is, so they coincide by construction.
- the HID driver no longer matches the boot subclass only. usb-tablet
declares subclass 0 and was refused at the door; hid_probe decides
what an interface actually is, and still declines what it cannot make
sense of.
- a non-boot HID interface is taken to be an absolute pointer and is
not asked for boot protocol, which it does not have -- that request
failing is what stopped it binding.
- tablet_report decodes the fixed 6-byte layout (buttons, 16-bit X,
16-bit Y, wheel) and scales the logical range to pixels there,
because it is the only place that knows the range.
- input_mouse_abs reports EV_ABS/ABS_X/ABS_Y so a reader can tell an
absolute position from a delta, and mouse_set_abs places the pointer
rather than nudging it.
- Schcom treats EV_ABS as authoritative and EV_REL as a nudge.
The device binds and identifies correctly: "usb-hid: tablet (absolute) on
slot 1, endpoint 0x81 every 4 ms".
It is NOT finished, and QEMU_INPUT is empty by default because of it. No
reports have yet been observed arriving on the tablet's interrupt
endpoint, so making it the default pointer would trade a cursor that
drifts for one that does not move at all. Opt in with
make qemu QEMU_INPUT='-device qemu-xhci,id=xhci -device usb-tablet,bus=xhci.0'
Next step is to find out why nothing arrives: whether the first transfer
is queued but never completes, whether a completion needs re-arming for
this endpoint, or whether QEMU is not routing motion to the tablet at all
(`info mice`).
bootcheck 108 [ok], schcom-test passes.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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| .. | ||
| Makefile | ||
| proto.h | ||
| README.md | ||
| schcom | ||
| schcom-demo | ||
| schcom-demo.c | ||
| schcom.c | ||
Schcom — the SchOS 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
v0 runs. A client connects, is given a shared buffer, draws into it and
commits; the result is composited and presented. Verified end to end by
make schcom-test, which boots SchOS, runs the compositor and a client, then
screendumps the framebuffer and asserts the pixels from the host — the
compositor's own report that it composited something proves nothing. It runs
two overlapping clients and checks that the newer one wins in the overlap: a
compositor that cannot order two surfaces cannot host a window manager.
What exists:
- framebuffer output through
/dev/fb0and the fbdev ioctls, double-buffered - a versioned protocol over a Unix socket, with a handshake that must come first
- shared-memory buffers, one per surface, owned by the compositor
- surface / attach / commit semantics: nothing is shown mid-draw
- input from
/dev/input/eventN, routed to the topmost surface - clients that die are cleaned up, including their shm segments
- multiple clients, composited bottom-to-top in creation order
What does not exist yet: damage tracking beyond "repaint everything", multiple outputs, subsurfaces, and any focus model beyond "topmost". Those are additions rather than rewrites, which is the reason for committing to the surface/commit model now instead of growing into it later.
Building
Not part of the OS build. Needs make ports first, for the sysroot's libc:
make projects # builds and stages into sysroot/bin
make # rebuilds the image so the binaries are on it
make schcom-test # boots it and checks the pixels
What it needs from the kernel
| Need | State |
|---|---|
Shared memory (shmget/shmat/shmdt) |
done |
mmap of /dev/fb0 |
done |
| Framebuffer geometry via the fbdev ioctls | done |
| Unix domain sockets | done |
| Raw input events — key down/up with modifiers | done |
SCM_RIGHTS |
done, and not yet used — see below |
| Mode setting and double buffering | partial — virtio-gpu binds, no modeset API yet |
Design notes
- 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.
- The compositor owns the segment, not the client. It has to survive a client crashing mid-frame, and it must not be something a client can resize underneath the compositor.
- One protocol, versioned from the start. SchWM and SchDE are separate programs, so this is a real compatibility surface on day one. Every message carries its own length, so an unknown message is skipped rather than desynchronising the stream — that is what lets a v0 compositor survive a v1 client.
- Policy belongs to SchWM. If Schcom starts deciding where windows go, the
split has already failed.
CREATE_SURFACEcarries x/y today only because there is no SchWM yet to ask.
On Wayland
The protocol is deliberately Wayland-shaped — surfaces rather than windows,
buffers attached and made visible only on commit, and the compositor telling
clients when to draw. Wayland is MIT-licensed, so it can be linked against
without any conflict with Apache-2.0 (see docs/architecture/licensing.md), and
supporting it later is intended.
The one place v0 knowingly diverges: a buffer handle is a System V shared memory
id passed as an integer, where Wayland passes a file descriptor over
SCM_RIGHTS. The kernel supports SCM_RIGHTS already; an integer simply needs
no ancillary-data handling on either side. struct schcom_surface carries a
handle_kind field precisely so that switching is a new value rather than a
protocol break.