Struct SceneDef 

pub struct SceneDef {

    pub id: &'static str,
    pub title: &'static str,
    pub description: &'static str,
    pub size: (u32, u32),
    pub baseline: Option<(u32, u32)>,
    pub clear: Option<Color>,
    pub frames: u32,
    pub step_seconds: Option<f32>,
    pub samples: u32,
    pub depth: bool,
    pub ui: bool,
    pub reproducible_ui: bool,
    pub build: Build,
}

One selectable scene.

The fields the snapshot tests draw the scene at — Self::size, Self::frames, Self::samples and Self::depth — reproduce the test the scene came from, so a captured frame is comparable with the snapshot it was stored against. The windowed path draws at the window’s own size instead, and only Self::build is shared.

Fields

id: &'static str

The scene’s stable id, used by --scene <ID>.

title: &'static str

A short title for the GUI and the scene list.

description: &'static str

What the scene shows, one line for the GUI.

size: (u32, u32)

The render target size the scene’s snapshots were captured at.

baseline: Option<(u32, u32)>

The aspect the windowed path keeps the scene’s 3D content at, as a reference resolution, or None for a scene that draws no 3D content and so has an aspect to keep.

A scene that declares one is drawn through the largest rectangle of that aspect that fits the window, so a wide window and a narrow one show the same picture — the wide one larger — instead of the wide one showing more. The snapshot tests ignore this and draw at Self::size, which the snapshots were captured at.

A UI-only scene declares none: an interface belongs on the whole window, and letterboxing it would put bars around a panel that has no aspect of its own.

clear: Option<Color>

The colour the scene’s pass clears to, or None to clear to the default.

A scene whose picture is painted over a particular backdrop declares one; every other scene leaves its pass at the default clear.

frames: u32

How many frames the snapshot tests draw before finishing.

step_seconds: Option<f32>

How long each frame stays on screen in the windowed loop, in seconds, or None for a scene that animates continuously from the frame delta.

The snapshot tests ignore this and draw the frames back to back, so a capture stays reproducible; the windowed path uses it so a scene whose frames were frozen as a sequence plays at a watchable pace rather than as fast as the display refreshes.

samples: u32

The sample count of the offscreen target the snapshot tests bind.

depth: bool

Whether that offscreen target carries a depth-stencil attachment.

ui: bool

Whether the scene draws UI panels of its own.

The snapshot tests mount a UI source to drive them; the windowed path always mounts one, for the scene selector.

reproducible_ui: bool

Whether the scene’s UI animates against egui’s clock.

A scene whose snapshots were captured with the clock suppressed — the example’s own, whose panels live in egui windows — declares true, so the snapshot tests zero egui’s animation time for it. The ported test scenes were captured with the clock live, and declare false.

build: Build

Build the scene’s world content and return its per-frame behaviour.

The world already holds the frame’s context, the renderer resource entity and the pass the scene draws through; the scene spawns its sources, meshes, camera and entities, sources inside the pass.

The entity is the UI source the shell mounted for the scene, when the run has one: a panel the scene draws hangs in that source’s scope, so the scene spawns it there rather than at the root — a source draws the subtree it owns and nothing beside it.