Struct BillboardCache 

pub struct BillboardCache {
    pub resolution: u32,
    pub snapshots: Vec<BillboardSnapshot>,
}

Per-grid lazy cache of 26 BillboardSnapshots indexed by the 26 canonical_viewpoints directions.

Construction modes:

• Self::new_empty: allocate an empty cache, populate later via Self::build.
• Self::build: render all 26 snapshots in one call. Use this from the render-time lazy path: when a grid first lands on Lod::Far, the S6.3 dispatch checks Grid::billboards; if None, calls build and stores.

Fields

resolution: u32

Snapshot resolution in pixels (square). Pinned at build time; rebuilds construct a fresh BillboardCache rather than resizing in place.

snapshots: Vec<BillboardSnapshot>

26 snapshots, indexed in the same order as canonical_viewpoints. Empty (Vec::new) iff this cache is uninitialised.

Implementations

impl BillboardCache

pub fn new_empty(resolution: u32) -> Self

Allocate an empty cache. snapshots is empty; future Self::build populates it. Cheap — no allocations beyond the empty Vec header.

pub fn len(&self) -> usize

Number of snapshots populated. 0 for an empty cache, 26 after Self::build.

pub fn is_empty(&self) -> bool

true iff this cache has not yet been populated (no snapshots stored).

pub fn build(grid: &Grid, resolution: u32) -> Self

Render all 26 viewpoint snapshots of grid into a fresh cache.

Cost: O(26 × resolution² × grid_render_cost). For resolution = 128 and a small ship grid this is roughly equivalent to a single full-frame render. Intended to be called once per grid-edit cycle (caches are invalidated on edits via Grid::set_voxel et al.).

An empty grid (no populated chunks) yields 26 all-sky snapshots. The cache is still populated so the S6.3 blit path doesn’t keep retrying — a Far-tier empty grid’s blit is then a no-op (every pixel skipped via SKY_SENTINEL).

Sky-pixel detection: the pool’s skycast colour is set to SKY_SENTINEL before each snapshot render so opticast writes the sentinel (not a real sky colour) into pixels rays missed. Post-render, every sentinel pixel’s depth is reset to f32::INFINITY (opticast writes a finite “sky distance” for these pixels, which would otherwise leak through the blit’s depth check).

pub fn pick_nearest(&self, query: DVec3) -> Option<&BillboardSnapshot>

Pick the snapshot whose view_dir is closest to query (largest dot product). Returns None iff the cache is empty.

query is the unit vector from the grid centre to the current camera position in grid-local space — the same frame the snapshot view_dirs live in. Caller is responsible for normalisation.

Tie-breaking is “first in viewpoint order”; with the 26 canonical viewpoints, ties only happen for query directions exactly equidistant between two viewpoints, which is a measure-zero set under f64.

Trait Implementations

impl Clone for BillboardCache

fn clone(&self) -> BillboardCache

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for BillboardCache

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

Formats the value using the given formatter.