Struct EstNormCache 

pub struct EstNormCache { /* private fields */ }

Pre-built expandbit256 grid covering a 2D bounding region — (x1 - x0 + 2*RAD) × (y1 - y0 + 2*RAD) columns. Trades 32 bytes per column of memory for O(1) bit-window lookups during the estnorm 5×5 neighbourhood vote.

This is the conceptual equivalent of voxlap’s xbsbuf cache — just batch-pre-built rather than rotated row-by-row through the bake. Memory cost stays manageable: a 448×448 bake (the diag_down_lit oracle scope, which extends to 452×452 with padding) needs about 6.4 MB.

Implementations

impl EstNormCache

pub fn build( world_data: &[u8], column_offsets: &[u32], vsid: u32, x0: i32, y0: i32, x1: i32, y1: i32, ) -> Self

Build the bit-grid cache covering the bounding region [x0..x1) × [y0..y1) extended by ESTNORMRAD padding on each side. Calling Self::estnorm for any (x, y) inside the original [x0..x1) × [y0..y1) box is then a pure read.

Wraps Self::build_with_reader with a flat-table closure.

pub fn build_with_reader<'r>( column_reader: impl Fn(i32, i32) -> Option<&'r [u8]>, x0: i32, y0: i32, x1: i32, y1: i32, ) -> Self

S4B.4.b: chunk-aware cache build. The closure column_reader(x, y) returns the slab bytes of the column at world-or-grid-local position (x, y), or None for an implicit-air / out-of-grid column (matching build’s OOB “treat as full air” semantics).

No vsid bound — the reader owns OOB handling. Per-chunk bakes use a closure that resolves (x, y) to a neighbour chunk via Grid::chunk(IVec3) so the 2-voxel padding extends seamlessly across chunk boundaries.

The cache’s Self::vsid field is left at 0 for chunk- aware builds — the field is dead-code anyway, preserved only for voxlap-parity inspection.

pub fn estnorm(&self, x: i32, y: i32, z: i32) -> [f32; 3]

Estimate the surface normal at (x, y, z) from a 5×5×5 voxel-solid neighbourhood vote. Mirror of voxlap5.c:1501 (estnorm, ESTNORMRAD == 2 branch).

(x, y) must lie inside the cache’s [x0..x1) × [y0..y1) region (panics otherwise — caller guarantees this via the bounding-box iteration). z is unconstrained (handled via air/solid clamping).