Raycast

CpuMeshBvh is one mesh's tree on the CPU, in the same layout the GPU reads. Raycasts, shapecasts, bvhcasts and closest points all run one walk and one triangle test. It needs no GPU and no engine; three's types pass where points, rays, boxes and matrices are asked for.

import { BVH_DOUBLE_SIDE, CpuMeshBvh, type MeshInput } from '@pmndrs/bvh';

const tree = await CpuMeshBvh.create(input, { maxLeafPrimitives: 8 }); // tinybvh, on this thread

Other ways to get one:

Quantized trees are decoded to 64-byte f32 nodes when the tree is made. Triangles are 48-byte records by default (indexed trees are expanded to them), each a copy of its corners. To keep 16 bytes per triangle instead, pass corners: 'positions' (to the constructor, build or create; it needs source): the tree keeps indexed triangles (tinybvh writes them, a records tree is converted) and reads every corner from source.positions by reference. Every query and refit gives the same answer bit for bit. The corners are then the source's live values, so after editing the positions call refit() before the next query; serialize() writes an indexed file, which loads with the same geometry as source. three's BvhBoundsTree does this for indexed trees on its own (The tree object).

const ray = { origin: [0, 0, 5], direction: [0, 0, -1] }; // or a three Ray
const hits = tree.raycast(ray, { side: BVH_DOUBLE_SIDE, near: 0, far: 100 }); // every hit, nearest first
const first = tree.raycastFirst(ray, BVH_DOUBLE_SIDE); // or null
if (first) console.log(first.distance, first.point, first.triangle, first.u, first.v, first.frontFace);

A layout from a file is checked when the tree is made (children in range, every node reached once, leaves and original indices within the triangles), so a corrupt one throws instead of hanging a walk.

Triangles are stored in tree order. resolveTriangleIndex(treePosition) maps a position (from traverse or bvhcast) to the original triangle, and treePositionOf(triangle) back. getTriangle(treePosition) returns the nine corner floats as the tree stores them. The source geometry is never reordered.

Raycasts per second, Node 22 on the Apple M5 while other jobs ran (bench/three-raycast.ts --seconds 2, three runs, median; a 100,000-triangle torus knot, rays from outside, 81% hit; indicative):

Next: Shapecast and bvhcast.