/**
 * Spatial chunk grid for batch bucketing (issue #1682, phase 2 of the
 * chunked-residency plan).
 *
 * Today a colour bucket spans the whole model, so its world AABB is
 * model-sized and per-batch frustum/contribution culling almost never fires.
 * Chunking adds a spatial dimension to the bucket key: meshes land in
 * `cell~colour` buckets, where `cell` is the axis-aligned grid cell of the
 * mesh's world anchor point. Batches become spatially compact, so the
 * existing per-batch culls (and, later, per-chunk residency/eviction) get
 * real purchase. A mesh is never split across cells — the anchor decides
 * membership for all of its vertices, exactly like the mesh-never-splits
 * rule in Cesium-style chunk planners.
 *
 * The anchor is `origin + first vertex`: `MeshData.positions` are stored in
 * the element's local frame with `world = origin + position` (see
 * `MeshData.origin`), so any vertex is a true world point of the mesh. The
 * first vertex is O(1), deterministic, and — unlike `localBounds` — needs no
 * placement transform (`localBounds` is a PRE-placement box, so
 * `origin + centre(localBounds)` would be wrong under rotation).
 *
 * Purely a reorganization: batches keep the shared scene frame origin, so
 * vertex relativization, the draw path, and highlight bit-coincidence are
 * untouched. Chunking multiplies batch count by the colours-per-cell factor;
 * cell size trades culling granularity against draw calls.
 */
/** Spatial slice of MeshData needed to derive a chunk cell. */
export interface ChunkAnchorSource {
    /** Element local-frame origin: world = origin + position. Absent = [0,0,0]. */
    origin?: [number, number, number];
    positions: Float32Array;
}
export interface SpatialChunkingConfig {
    /** Grid cell edge length in world units (metres for IFC models). */
    cellSize: number;
}
/**
 * Default cell edge. Big enough that a small building stays one cell per
 * colour (zero draw-call growth on FZK-class models), small enough that a
 * city-block model splits into cullable tiles. Tune against the benchmark's
 * drawCalls metric before flipping the feature default on.
 */
export declare const DEFAULT_CHUNK_CELL_SIZE = 32;
/**
 * Grid cell key ("cx,cy,cz") of the mesh's world anchor point.
 * Empty meshes anchor at their origin. NaN coordinates land in a dedicated
 * "nan" cell rather than poisoning arithmetic downstream.
 */
export declare function chunkCellKey(mesh: ChunkAnchorSource, cellSize: number): string;
/**
 * Bucket BASE key for a mesh (before any "#N" overflow suffix from
 * `resolveActiveBucket`): plain colour key when chunking is off,
 * `cell~colour` when on. Every bucket-key derivation site in the Scene MUST
 * go through this so a mesh resolves to the same bucket during streaming,
 * finalize re-grouping, recolour moves, and partial-batch piece filtering.
 * ("~" cannot collide: colour keys are `r|g|b|a` integers, cell keys are
 * `cx,cy,cz` integers, and the overflow suffix uses "#".)
 */
export declare function bucketBaseKeyFor(mesh: ChunkAnchorSource, colorKey: string, chunking: SpatialChunkingConfig | null): string;
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