old_contents: import {
  	Matrix4,
  	Mesh,
  	MeshBasicMaterial
  } from 'three';
  
  /**
   * A shadow Mesh that follows a shadow-casting Mesh in the scene, but is confined to a single plane.
   */
  
  const _shadowMatrix = new Matrix4();
  
  class ShadowMesh extends Mesh {
  
  	constructor( mesh ) {
  
  		const shadowMaterial = new MeshBasicMaterial( {
  
  			color: 0x000000,
  			transparent: true,
  			opacity: 0.6,
  			depthWrite: false
  
  		} );
  
  		super( mesh.geometry, shadowMaterial );
  
  		this.isShadowMesh = true;
  
  		this.meshMatrix = mesh.matrixWorld;
  
  		this.frustumCulled = false;
  		this.matrixAutoUpdate = false;
  
  	}
  
  	update( plane, lightPosition4D ) {
  
  		// based on https://www.opengl.org/archives/resources/features/StencilTalk/tsld021.htm
  
  		const dot = plane.normal.x * lightPosition4D.x +
  			  plane.normal.y * lightPosition4D.y +
  			  plane.normal.z * lightPosition4D.z +
  			  - plane.constant * lightPosition4D.w;
  
  		const sme = _shadowMatrix.elements;
  
  		sme[ 0 ] = dot - lightPosition4D.x * plane.normal.x;
  		sme[ 4 ] = - lightPosition4D.x * plane.normal.y;
  		sme[ 8 ] = - lightPosition4D.x * plane.normal.z;
  		sme[ 12 ] = - lightPosition4D.x * - plane.constant;
  
  		sme[ 1 ] = - lightPosition4D.y * plane.normal.x;
  		sme[ 5 ] = dot - lightPosition4D.y * plane.normal.y;
  		sme[ 9 ] = - lightPosition4D.y * plane.normal.z;
  		sme[ 13 ] = - lightPosition4D.y * - plane.constant;
  
  		sme[ 2 ] = - lightPosition4D.z * plane.normal.x;
  		sme[ 6 ] = - lightPosition4D.z * plane.normal.y;
  		sme[ 10 ] = dot - lightPosition4D.z * plane.normal.z;
  		sme[ 14 ] = - lightPosition4D.z * - plane.constant;
  
  		sme[ 3 ] = - lightPosition4D.w * plane.normal.x;
  		sme[ 7 ] = - lightPosition4D.w * plane.normal.y;
  		sme[ 11 ] = - lightPosition4D.w * plane.normal.z;
  		sme[ 15 ] = dot - lightPosition4D.w * - plane.constant;
  
  		this.matrix.multiplyMatrices( _shadowMatrix, this.meshMatrix );
  
  	}
  
  }
  
  export { ShadowMesh };
  
new_contents: import {
  	Matrix4,
  	Mesh,
  	MeshBasicMaterial,
  	EqualStencilFunc,
  	IncrementStencilOp
  } from 'three';
  
  /**
   * A shadow Mesh that follows a shadow-casting Mesh in the scene, but is confined to a single plane.
   */
  
  const _shadowMatrix = new Matrix4();
  
  class ShadowMesh extends Mesh {
  
  	constructor( mesh ) {
  
  		const shadowMaterial = new MeshBasicMaterial( {
  
  			color: 0x000000,
  			transparent: true,
  			opacity: 0.6,
  			depthWrite: false,
  			stencilWrite: true,
              		stencilFunc: EqualStencilFunc,
              		stencilRef: 0,
              		stencilZPass: IncrementStencilOp
  
  		} );
  
  		super( mesh.geometry, shadowMaterial );
  
  		this.isShadowMesh = true;
  
  		this.meshMatrix = mesh.matrixWorld;
  
  		this.frustumCulled = false;
  		this.matrixAutoUpdate = false;
  
  	}
  
  	update( plane, lightPosition4D ) {
  
  		// based on https://www.opengl.org/archives/resources/features/StencilTalk/tsld021.htm
  
  		const dot = plane.normal.x * lightPosition4D.x +
  			  plane.normal.y * lightPosition4D.y +
  			  plane.normal.z * lightPosition4D.z +
  			  - plane.constant * lightPosition4D.w;
  
  		const sme = _shadowMatrix.elements;
  
  		sme[ 0 ] = dot - lightPosition4D.x * plane.normal.x;
  		sme[ 4 ] = - lightPosition4D.x * plane.normal.y;
  		sme[ 8 ] = - lightPosition4D.x * plane.normal.z;
  		sme[ 12 ] = - lightPosition4D.x * - plane.constant;
  
  		sme[ 1 ] = - lightPosition4D.y * plane.normal.x;
  		sme[ 5 ] = dot - lightPosition4D.y * plane.normal.y;
  		sme[ 9 ] = - lightPosition4D.y * plane.normal.z;
  		sme[ 13 ] = - lightPosition4D.y * - plane.constant;
  
  		sme[ 2 ] = - lightPosition4D.z * plane.normal.x;
  		sme[ 6 ] = - lightPosition4D.z * plane.normal.y;
  		sme[ 10 ] = dot - lightPosition4D.z * plane.normal.z;
  		sme[ 14 ] = - lightPosition4D.z * - plane.constant;
  
  		sme[ 3 ] = - lightPosition4D.w * plane.normal.x;
  		sme[ 7 ] = - lightPosition4D.w * plane.normal.y;
  		sme[ 11 ] = - lightPosition4D.w * plane.normal.z;
  		sme[ 15 ] = dot - lightPosition4D.w * - plane.constant;
  
  		this.matrix.multiplyMatrices( _shadowMatrix, this.meshMatrix );
  
  	}
  
  }
  
  export { ShadowMesh };
  
subject: Improve ShadowMesh.js and Prevent Shadow Overlap (#24180)