Struct ShmSurface 

struct ShmSurface {
    shmseg: u32,
    addr: *mut u8,
    size: usize,
    width: u16,
    height: u16,
    stride: usize,
}

A shared-memory image surface: a POSIX shm segment mapped into both this process and the X server, into which shm_get_image writes one BGRA frame.

Both ends map the same physical pages, which is the whole point: a full-screen grab then costs no per-frame copy across the X socket, because the server’s blit lands directly in memory the capture thread already reads. The surface owns the server-side segment id (shmseg), the local mapping (addr / size), and the geometry (width / height / stride) needed to interpret the bytes.

Fields

shmseg: u32

addr: *mut u8

size: usize

width: u16

height: u16

stride: usize

Implementations

impl ShmSurface

fn create( conn: &RustConnection, width: u16, height: u16, ) -> Result<Self, String>

Allocate a shm segment of width*height*4 bytes, attach it both locally and to the X server, and hand back a surface both ends can read.

The segment is created with shmget(IPC_PRIVATE) and mapped locally via shmat, then attached on the server (shm_attach). That attach is confirmed with a round-trip check() BEFORE the segment is marked IPC_RMID: deleting only after both ends hold a reference means the kernel frees the segment once this process and the server have both detached, never while either still needs it. Every failure path unwinds the partial state (local detach and/or IPC_RMID) so a failed allocation leaks neither memory nor a server attachment; a zero-sized request is rejected up front.

fn as_mut_slice(&mut self) -> &mut [u8]

Borrow the mapped segment as a mutable byte slice for the capture blit and overlays.

fn as_slice(&self) -> &[u8]

Borrow the mapped segment read-only, for the stability comparison.

fn destroy(&mut self, conn: &RustConnection)

Detach the segment from the X server and then locally, clearing the mapped pointer.

This is a manual method rather than a Drop impl because releasing the server-side attachment is an X protocol request that needs the live connection, which a Drop could not reach; the owner of the connection must call it before the surface is dropped. The order — server shm_detach first, then the local shmdt — completes the release of the segment that was marked IPC_RMID at creation, so the kernel reclaims it once neither end holds it.