three.js/examples/jsm/csm/FrustumBoundingBox.js

export default class FrustumBoundingBox {

	constructor() {

		this.min = {
			x: 0,
			y: 0,
			z: 0
		};
		this.max = {
			x: 0,
			y: 0,
			z: 0
		};

	}

	fromFrustum( frustum ) {

		const vertices = [];

		for ( let i = 0; i < 4; i ++ ) {

			vertices.push( frustum.vertices.near[ i ] );
			vertices.push( frustum.vertices.far[ i ] );

		}

		this.min = {
			x: vertices[ 0 ].x,
			y: vertices[ 0 ].y,
			z: vertices[ 0 ].z
		};
		this.max = {
			x: vertices[ 0 ].x,
			y: vertices[ 0 ].y,
			z: vertices[ 0 ].z
		};

		for ( let i = 1; i < 8; i ++ ) {

			this.min.x = Math.min( this.min.x, vertices[ i ].x );
			this.min.y = Math.min( this.min.y, vertices[ i ].y );
			this.min.z = Math.min( this.min.z, vertices[ i ].z );
			this.max.x = Math.max( this.max.x, vertices[ i ].x );
			this.max.y = Math.max( this.max.y, vertices[ i ].y );
			this.max.z = Math.max( this.max.z, vertices[ i ].z );

		}

		return this;

	}

	getSize() {

		this.size = {
			x: this.max.x - this.min.x,
			y: this.max.y - this.min.y,
			z: this.max.z - this.min.z
		};

		return this.size;

	}

	getCenter( margin ) {

		this.center = {
			x: ( this.max.x + this.min.x ) / 2,
			y: ( this.max.y + this.min.y ) / 2,
			z: this.max.z + margin
		};

		return this.center;

	}

}