> ## Documentation Index
> Fetch the complete documentation index at: https://docs.otter-shell.org/llms.txt
> Use this file to discover all available pages before exploring further.

# SHM and damage

> WaylandShmPool, DamageTracker, and Renderer in otter-wayland.

## SHM pools

Two pool types share the same acquire API:

| Pool            | Use                                                              |
| --------------- | ---------------------------------------------------------------- |
| `DoubleShmPool` | Interactive surfaces (bar, launcher, settings)                   |
| `SingleShmPool` | Static content (wallpaper). `forceReleaseAll()` for rare redraws |

```zig theme={null}
self.shm_pool = try otter_wayland.DoubleShmPool.init(.{
    .wl_shm = wl_shm,
    .width = 800,
    .height = 600,
    .scale = 2,
    .name = "my-surface",
});
self.shm_pool.?.bindListeners(); // after struct is at final address

if (self.shm_pool.?.acquire()) |acquired| {
    var surface = render.Surface.fromPixelsScaledWithStride(
        acquired.pixels,
        pool.physicalWidth(),
        pool.physicalHeight(),
        acquired.stride_pixels,
        scale,
    );
    wl_surface.attach(acquired.wl_buffer, 0, 0);
    wl_surface.damageBuffer(0, 0, pool.physicalWidth(), pool.physicalHeight());
    wl_surface.commit();
}
```

Row stride is 256-byte aligned. Use `acquired.stride_pixels` when wrapping pixels.

`resizeWithScale` requires all buffers to be free.

## DamageTracker

Accumulates dirty rectangles for partial redraws. Overflow falls back to full-surface damage.

```zig theme={null}
var tracker = otter_wayland.DamageTracker.init(width, height);
tracker.addRect(dirty);
const rects = tracker.rects();
const full = tracker.needsFullRedraw();
```

Pass rects to `otter-render` `quad_renderer` and `wl_surface.damageBuffer`.

## Renderer helper

`createRenderer` ties pool acquire, `UiState.rasterize`, and commit into one path for simple apps. Most apps still manage pools explicitly for custom damage.