Refits

import { GpuBvhRefit, leafSlotsOf, parentSlotsOf, type GpuLayoutMeshBvh } from '@pmndrs/bvh';

const refit = new GpuBvhRefit(device);
await refit.prepare();

// Once per tree shape, from a CPU copy of the tree:
const words = new Uint32Array(layout.nodes);
refit.setShape({
    nodeWordOffset: 0,
    nodeCount: layout.nodeCount,
    parentSlots: parentSlotsOf(words, 0, layout.nodeCount, layout.parents),
    leafSlots: leafSlotsOf(words, 0, layout.nodeCount),
    generation: 1,
});

// Every frame, after a pass wrote one box per primitive (8 floats: min x, y, z, unused,
// max x, y, z, unused), in the order the tree's leaves index them:
refit.encode(pass, treeBuffer, primitiveBoxes);

import { GpuMeshRefit } from '@pmndrs/bvh';

const meshRefit = new GpuMeshRefit(device, { diagnostics: true });
await meshRefit.prepare();
// Once, from a CPU copy of the tree (any builder's), in its own buffers:
meshRefit.setTree(layout);
// For a mesh inside a scene's buffers, the placement says where, and in what node format:
// meshRefit.setTree(layout, meshRefitPlacement(scene, meshIndex));

// Every frame, after the pass that writes the moved vertices:
meshRefit.pollStats(); // maps an earlier frame's stats copy, without waiting
const encoder = device.createCommandEncoder();
const pass = encoder.beginComputePass();
meshRefit.encode(pass, { nodes: nodeBuffer, triangles: triangleBuffer }, { positionBuffer: skinnedPositions, vertexCount, indexBuffer, indexFormat: 'uint32' });
pass.end();
meshRefit.copyStats(encoder); // with diagnostics only
device.queue.submit([encoder.finish()]);

// A frame or two late: the refit tree's SAH cost over its root's area. Rebuild when it drifts up.
const cost = meshRefit.latestStats?.relativeCost;