Struct StreamRadius 

pub struct StreamRadius {
    pub r_active: f64,
    pub r_evict: f64,
}

Per-grid streaming activity / eviction radii (S7.1).

Both values are in grid-local voxel units — the same scale as a GridLocalPos::voxel coordinate. The math falls out cleanly from there: chunks span fixed integer voxel extents and the camera’s grid-local position is also expressed in voxels.

Semantics inside crate::Scene::pump_streaming_sync:

• A chunk whose AABB-to-camera distance is ≤ r_active MUST be loaded; if absent + a generator is attached, it gets streamed in via crate::Grid::ensure_chunk_generated.
• A chunk whose AABB-to-camera distance is > r_evict is dropped from the chunk map.
• Chunks in the hysteresis band (r_active, r_evict] are neither streamed in nor evicted — they’re left as-is. The gap prevents a camera oscillating near a boundary from thrashing generation + eviction.

The Default / Self::DISABLED value is r_active = 0, r_evict = ∞: crate::Scene::pump_streaming_sync is a no-op. Existing grids keep the pre-S7 “absent stays absent, present stays present” behaviour until a caller opts in.

Fields

r_active: f64

Chunks closer than this (grid-local voxels, AABB distance) are streamed in.

r_evict: f64

Chunks farther than this (grid-local voxels, AABB distance) are evicted. Must be ≥ r_active.

Implementations

impl StreamRadius

pub const DISABLED: Self

r_active = 0, r_evict = ∞ — pump_streaming_sync never streams a chunk in or evicts one. The default for pre-S7.1 grids.

pub fn new(r_active: f64, r_evict: f64) -> Self

New radius pair. Requires r_evict >= r_active so the hysteresis band is well-formed (or empty when ==).

Panics

Panics if r_evict < r_active, if r_active is NaN or negative, or if r_evict is negative. NaN and negative radii are policy bugs — failing loud at construction beats silently degenerating chunk-AABB tests later.

Examples found in repository

examples/book_scene_graph.rs (line 172)

fn main() {
    // ANCHOR: scene_grids
    let mut scene = Scene::new();
    // A static "world" grid at the origin…
    let ground_id = scene.add_grid(GridTransform::at(DVec3::ZERO));
    // …and a second grid placed and rotated independently — its own
    // f64 world position + quaternion, same chunked voxel payload.
    let ship_id = scene.add_grid(GridTransform {
        origin: DVec3::new(300.0, -80.0, -40.0),
        rotation: DQuat::from_rotation_z(0.5),
    });
    // Object grids should not paint their own (grid-local, rotating)
    // sky — leave the sky to the world grid.
    scene.grid_mut(ship_id).expect("just added").render_sky = false;
    // ANCHOR_END: scene_grids

    // ANCHOR: edits
    let ground = scene.grid_mut(ground_id).expect("just added");
    // Solid slab: grid-local voxel coords, inclusive on both ends,
    // decomposed across as many chunks as it spans (here 4×4).
    ground.set_rect(
        IVec3::new(-200, -200, 200),
        IVec3::new(199, 199, 254),
        Some(GRASS),
    );
    // `Some(colour)` inserts, `None` carves back to air.
    ground.set_sphere(IVec3::new(0, 0, 195), 12, Some(STONE));
    ground.set_rect(IVec3::new(-3, -200, 190), IVec3::new(3, 199, 196), None);
    // ANCHOR_END: edits

    // ANCHOR: queries
    // Solid tests: inside the slab, then inside the carved tunnel.
    assert!(ground.voxel_solid(IVec3::new(0, 0, 210)));
    assert!(!ground.voxel_solid(IVec3::new(0, 100, 193)));
    // Colour queries answer on surface voxels; deep interior cells
    // are untextured in the slab format and read as `None`.
    assert_eq!(ground.voxel_color(IVec3::new(50, 50, 200)), Some(GRASS));
    // ANCHOR_END: queries

    // ANCHOR: recolour
    // GOTCHA: inserting over already-solid voxels does NOT repaint
    // them — span insertion only fills air. Recolour = carve, then
    // insert.
    let (lo, hi) = (IVec3::new(20, 20, 200), IVec3::new(24, 24, 204));
    ground.set_rect(lo, hi, Some(RED));
    assert_eq!(ground.voxel_color(IVec3::new(22, 22, 200)), Some(GRASS)); // unchanged!
    ground.set_rect(lo, hi, None); // carve…
    ground.set_rect(lo, hi, Some(RED)); // …then insert
    assert_eq!(ground.voxel_color(IVec3::new(22, 22, 200)), Some(RED));
    // ANCHOR_END: recolour

    // ANCHOR: colfunc
    // A carve exposes fresh interior walls; the plain edits paint
    // them colour 0 (black). The `_with_colfunc` variants ask a
    // closure instead — it sees grid-local coordinates, so gradients
    // stay continuous across chunk seams. Here: a crater whose walls
    // darken with depth.
    ground.set_sphere_with_colfunc(IVec3::new(60, 60, 200), 8, SpanOp::Carve, |_x, _y, z| {
        let depth = (z - 192).clamp(0, 15) as u8;
        VoxColor::rgb(0x6b, 0x40 + depth * 3, 0x2f)
    });
    // ANCHOR_END: colfunc

    // ANCHOR: snapshot
    // Name grids before saving: ids survive the round-trip, but the
    // generator / store hooks are host code and cannot be serialised
    // — the name is your key for rebinding them after a load.
    scene.grid_mut(ground_id).expect("ground exists").name = Some("ground".into());
    let bytes = scene.save_snapshot(); // versioned envelope
    let restored = Scene::load_snapshot(&bytes).expect("self-authored snapshot");
    assert_eq!(restored.grid_count(), 2);
    let (_, ground2) = restored
        .grids()
        .find(|(_, g)| g.name.as_deref() == Some("ground"))
        .expect("rebind by name");
    assert_eq!(ground2.voxel_color(IVec3::new(22, 22, 200)), Some(RED));
    // ANCHOR_END: snapshot

    // ANCHOR: streaming
    // Streaming: attach a generator + radii to a grid, then pump once
    // per frame with the camera's world position. Chunks within
    // `r_active` stream in; chunks beyond `r_evict` drop out; the band
    // between is hysteresis so a camera hovering on a boundary
    // doesn't thrash.
    let stream_id = scene.add_grid(GridTransform::at(DVec3::new(0.0, 4096.0, 0.0)));
    let store = Arc::new(MemoryStore::default());
    let grid = scene.grid_mut(stream_id).expect("just added");
    grid.set_generator(Some(Arc::new(FloorGenerator)));
    grid.set_chunk_store(Some(store));
    grid.stream_radius = StreamRadius::new(256.0, 384.0);

    let camera_near = DVec3::new(0.0, 4096.0, 100.0);
    scene.pump_streaming_sync(camera_near); // real games: `pump_streaming`
    let grid = scene.grid(stream_id).expect("still there");
    assert!(grid.chunk_count() > 0); // floor streamed in around the camera
    assert!(grid.voxel_solid(IVec3::new(5, 5, 240)));
    // ANCHOR_END: streaming

    // ANCHOR: streaming_edit
    // Edit the streamed floor, walk far away, come back. The active
    // set follows the camera: the old region evicts (edited chunks
    // are handed to the ChunkStore first) while a fresh set streams
    // in around the new position. On return the store wins over the
    // generator, so the edit survives; without a store, eviction
    // would silently revert the chunk to generator output.
    scene
        .grid_mut(stream_id)
        .expect("still there")
        .set_voxel(IVec3::new(5, 5, 240), None); // dig a hole
    scene.pump_streaming_sync(camera_near + DVec3::new(0.0, 100_000.0, 0.0));
    let grid = scene.grid(stream_id).expect("still there");
    assert!(grid.chunk(IVec3::ZERO).is_none()); // home chunk evicted…
    assert!(grid.chunk_count() > 0); // …but the far region streamed in
    scene.pump_streaming_sync(camera_near);
    let grid = scene.grid(stream_id).expect("re-streamed");
    // The hole survived evict + re-stream.
    assert!(!grid.voxel_solid(IVec3::new(5, 5, 240)));
    // ANCHOR_END: streaming_edit

    println!("book_scene_graph: all scene-graph assertions hold");
}

pub fn is_disabled(self) -> bool

true for the Self::DISABLED sentinel pair. Lets pump_streaming_sync skip the per-grid pass cheaply when streaming is off.

Trait Implementations

impl Clone for StreamRadius

fn clone(&self) -> StreamRadius

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for StreamRadius

impl Debug for StreamRadius

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for StreamRadius

fn default() -> Self

Returns the “default value” for a type.

impl<'de> Deserialize<'de> for StreamRadius

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl PartialEq for StreamRadius

fn eq(&self, other: &StreamRadius) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Serialize for StreamRadius

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl StructuralPartialEq for StreamRadius