@three.ez/batched-mesh-extensions/src/core/feature/LOD.js

Utility extension methods for BatchedMesh

export function addGeometryLOD(geometryId, geoOrIndex, distance, hysteresis = 0) {
    const geometryInfo = this._geometryInfo[geometryId];
    const srcIndexArray = geoOrIndex.isBufferGeometry ? geoOrIndex.index.array : geoOrIndex;
    distance = distance ** 2;
    geometryInfo.LOD ?? (geometryInfo.LOD = [{ start: geometryInfo.start, count: geometryInfo.count, distance: 0, hysteresis: 0 }]);
    const LOD = geometryInfo.LOD;
    const lastLOD = LOD[LOD.length - 1];
    const start = lastLOD.start + lastLOD.count;
    const count = srcIndexArray.length;
    if ((start - geometryInfo.start) + count > geometryInfo.reservedIndexCount) {
        throw new Error('BatchedMesh LOD: Reserved space request exceeds the maximum buffer size.');
    }
    LOD.push({ start, count, distance, hysteresis });
    const dstIndex = this.geometry.getIndex();
    const dstIndexArray = dstIndex.array;
    const vertexStart = geometryInfo.vertexStart;
    for (let i = 0; i < count; i++) {
        dstIndexArray[start + i] = srcIndexArray[i] + vertexStart;
    }
    dstIndex.needsUpdate = true;
}
export function getLODIndex(LODs, distance) {
    for (let i = LODs.length - 1; i > 0; i--) {
        const level = LODs[i];
        const levelDistance = level.distance - (level.distance * level.hysteresis);
        if (distance >= levelDistance)
            return i;
    }
    return 0;
}
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