Struct SubsurfaceSpec

pub struct SubsurfaceSpec<Message: Clone> {
    pub id: SubsurfaceId,
    pub parent: SubsurfaceParent,
    pub view: Element<Message>,
    pub x: i32,
    pub y: i32,
    pub content_version: u64,
    pub gpu: bool,
}

An input-transparent child surface composited over the main surface and moved by the compositor.

Returned from App::subsurfaces. The runtime creates one wl_subsurface per active spec, full-size over the main surface, with an empty input region — all pointer/touch falls through to the main surface, so the host keeps a single input/gesture model. The win is in the move: the content buffer is rasterised only when content_version (or the surface size) changes, while x / y changes only emit wl_subsurface.set_position + a parent commit — no re-raster, no buffer re-upload. This makes an animated reveal/slide track the finger at the compositor’s compositing cost rather than the client’s raster cost.

Fields

id: SubsurfaceId

Stable identifier, used to diff subsurfaces between frames.

parent: SubsurfaceParent

Surface this subsurface is composited as a child of. Sized to that parent; x / y are relative to its top-left.

view: Element<Message>

Widget tree for this subsurface. Should paint its own opaque background if it must cover the main surface beneath it.

x: i32

Position of the subsurface relative to the parent’s top-left, in layout (physical) pixels — the same space as App::on_resize and widget rects. The runtime divides by the surface scale to obtain the logical position it hands to the compositor. Animate this for a cheap compositor-side move.

y: i32

content_version: u64

Content revision. Bump it whenever view would paint differently; leave it unchanged for position-only updates so the runtime skips the re-raster and only repositions.

gpu: bool

Render through GLES (so backdrop-filter glass works) rather than the software rasteriser. GLES is only worth it for content that actually uses the blur: it pays a per-surface EGL-surface creation (and a one-time shader compile) the cheap software path avoids, so a panel without glass should leave this false.