Window And Protocol Surfaces
Windowing, surface, and display protocol ABI
SlopOS windowing has three layers:
| Layer | Role |
|---|---|
| Kernel ABI structs | Shared state and constants |
| Wire protocol | Display protocol v2 request/event encoding |
| Client runtime | Raw windows, surfaces, event loop, widgets |
Kernel Window ABI
WindowInfo is the shared window metadata structure. It includes task id,
position, content size, window state, cursor shape, shared-memory token, damage
regions, title, app id, and compositor-provided frame dimensions.
Important constants:
| Constant | Meaning |
|---|---|
MAX_WINDOW_DAMAGE_REGIONS | Per-window damage-region cap |
MAX_BUFFER_AGE | Buffer-age bound |
WINDOW_STATE_NORMAL | Normal toplevel |
WINDOW_STATE_MINIMIZED | Minimized toplevel |
WINDOW_STATE_MAXIMIZED | Maximized toplevel |
CURSOR_SHAPE_* | Cursor shape ids from default through resize shapes |
SurfaceRole follows Wayland-style role assignment: None, Toplevel,
Popup, and Subsurface. Roles are not intended to change once assigned.
Display Protocol V2
slop-protocol is a length-prefixed little-endian binary protocol. It includes:
| Request group | Examples |
|---|---|
| Handshake | Hello { version } |
| Surface lifecycle | create, attach, damage, commit, frame, destroy |
| Toplevel lifecycle | get toplevel, set title, set app id, ack configure, destroy |
| Cursor | set cursor shape |
| Clipboard | copy, paste, read via memfd-backed buffers |
| Interactive actions | move and resize authorized by input serials |
Server events include hello/capabilities, output info, configure, input events, frame callbacks, clipboard readiness/results, and protocol errors.
Buffer Passing
Window buffers use memfd_create, ftruncate, and mmap(MAP_SHARED).
Protocol messages that transfer a buffer fd use AF_UNIX ancillary data. The
receiver wraps fds in OwnedFd so file descriptors are closed on drop unless
explicitly consumed.
Runtime Crates
- The windowing runtime exposes raw windows, surfaces, protocol handles, and event-loop helpers.
- AppKit exposes retained UI nodes, layout constraints, input/focus handling, widget traits, and app launch helpers.