three.js/examples/jsm/csm/Frustum.js

import * as THREE from '../../../build/three.module.js';
import FrustumVertex from './FrustumVertex.js';
import {toRad} from './Utils.js';

export default class Frustum {
	constructor(data) {
		data = data || {};

		this.fov = data.fov || 70;
		this.near = data.near || 0.1;
		this.far = data.far || 1000;
		this.aspect = data.aspect || 1;

		this.vertices = {
			near: [],
			far: []
		};
	}

	getViewSpaceVertices() {
		this.nearPlaneY = this.near * Math.tan(toRad(this.fov / 2));
		this.nearPlaneX = this.aspect * this.nearPlaneY;

		this.farPlaneY = this.far * Math.tan(toRad(this.fov / 2));
		this.farPlaneX = this.aspect * this.farPlaneY;

		// 3 --- 0  vertices.near/far order
		// |     |
		// 2 --- 1

		this.vertices.near.push(
			new FrustumVertex(this.nearPlaneX, this.nearPlaneY, -this.near),
			new FrustumVertex(this.nearPlaneX, -this.nearPlaneY, -this.near),
			new FrustumVertex(-this.nearPlaneX, -this.nearPlaneY, -this.near),
			new FrustumVertex(-this.nearPlaneX, this.nearPlaneY, -this.near)
		);

		this.vertices.far.push(
			new FrustumVertex(this.farPlaneX, this.farPlaneY, -this.far),
			new FrustumVertex(this.farPlaneX, -this.farPlaneY, -this.far),
			new FrustumVertex(-this.farPlaneX, -this.farPlaneY, -this.far),
			new FrustumVertex(-this.farPlaneX, this.farPlaneY, -this.far)
		);

		return this.vertices;
	}

	split(breaks) {
		const result = [];

		for(let i = 0; i < breaks.length; i++) {
			const cascade = new Frustum();

			if(i === 0) {
				cascade.vertices.near = this.vertices.near;
			} else {
				for(let j = 0; j < 4; j++) {
					cascade.vertices.near.push(new FrustumVertex().fromLerp(this.vertices.near[j], this.vertices.far[j], breaks[i - 1]));
				}
			}

			if(i === breaks - 1) {
				cascade.vertices.far = this.vertices.far;
			} else {
				for(let j = 0; j < 4; j++) {
					cascade.vertices.far.push(new FrustumVertex().fromLerp(this.vertices.near[j], this.vertices.far[j], breaks[i]))
				}
			}

			result.push(cascade);
		}

		return result;
	}

	toSpace(cameraMatrix) {
		const result = new Frustum();
		const point = new THREE.Vector3();

		for(var i = 0; i < 4; i++) {
			point.set(this.vertices.near[i].x, this.vertices.near[i].y, this.vertices.near[i].z);
			point.applyMatrix4(cameraMatrix);
			result.vertices.near.push(new FrustumVertex(point.x, point.y, point.z));

			point.set(this.vertices.far[i].x, this.vertices.far[i].y, this.vertices.far[i].z);
			point.applyMatrix4(cameraMatrix);
			result.vertices.far.push(new FrustumVertex(point.x, point.y, point.z));
		}

		return result;
	}
}