@polygonjs/polygonjs/src/core/Hash.ts

node-based WebGL 3D engine https://polygonjs.com

/*

adapted from https://github.com/matthias-research/pages/blob/master/tenMinutePhysics/12-softBodySkinning.html

*/

import {TypedArray} from 'three';
import {Number3} from '../types/GlobalTypes';

export interface HashOptions {
	spacing: number;
	maxNumObjects: number;
}

export class Hash {
	private spacing: number;
	private tableSize: number;
	private cellStart: Int32Array;
	private cellEntries: Int32Array;
	public readonly queryIds: Int32Array;
	private querySize: number;
	constructor(options: HashOptions) {
		const {spacing, maxNumObjects} = options;
		this.spacing = spacing;
		this.tableSize = 2 * maxNumObjects;
		this.cellStart = new Int32Array(this.tableSize + 1);
		this.cellEntries = new Int32Array(maxNumObjects);
		this.queryIds = new Int32Array(maxNumObjects);
		this.querySize = 0;
	}

	hashCoords(xi: number, yi: number, zi: number) {
		var h = (xi * 92837111) ^ (yi * 689287499) ^ (zi * 283923481); // fantasy function
		return Math.abs(h) % this.tableSize;
	}

	intCoord(coord: number) {
		return Math.floor(coord / this.spacing);
	}

	hashPos(pos: TypedArray, nr: number) {
		return this.hashCoords(
			this.intCoord(pos[3 * nr]),
			this.intCoord(pos[3 * nr + 1]),
			this.intCoord(pos[3 * nr + 2])
		);
	}

	create(pos: TypedArray) {
		var numObjects = Math.min(pos.length / 3, this.cellEntries.length);

		// determine cell sizes

		this.cellStart.fill(0);
		this.cellEntries.fill(0);

		for (var i = 0; i < numObjects; i++) {
			var h = this.hashPos(pos, i);
			this.cellStart[h]++;
		}

		// determine cells starts

		var start = 0;
		for (var i = 0; i < this.tableSize; i++) {
			start += this.cellStart[i];
			this.cellStart[i] = start;
		}
		this.cellStart[this.tableSize] = start; // guard

		// fill in objects ids

		for (var i = 0; i < numObjects; i++) {
			var h = this.hashPos(pos, i);
			this.cellStart[h]--;
			this.cellEntries[this.cellStart[h]] = i;
		}
	}

	query(pos: Number3, nr: number, maxDist: number) {
		var x0 = this.intCoord(pos[3 * nr] - maxDist);
		var y0 = this.intCoord(pos[3 * nr + 1] - maxDist);
		var z0 = this.intCoord(pos[3 * nr + 2] - maxDist);

		var x1 = this.intCoord(pos[3 * nr] + maxDist);
		var y1 = this.intCoord(pos[3 * nr + 1] + maxDist);
		var z1 = this.intCoord(pos[3 * nr + 2] + maxDist);

		this.querySize = 0;

		for (var xi = x0; xi <= x1; xi++) {
			for (var yi = y0; yi <= y1; yi++) {
				for (var zi = z0; zi <= z1; zi++) {
					var h = this.hashCoords(xi, yi, zi);
					var start = this.cellStart[h];
					var end = this.cellStart[h + 1];

					for (var i = start; i < end; i++) {
						this.queryIds[this.querySize] = this.cellEntries[i];
						this.querySize++;
					}
				}
			}
		}
	}
}