https://github.com/WWBN/AVideo/issues/8713

node_modules/three/examples/js/objects/ShadowMesh.js

@@ -0,0 +1,67 @@
+/**
+ * A shadow Mesh that follows a shadow-casting Mesh in the scene, but is confined to a single plane.
+ */
+
+THREE.ShadowMesh = function ( mesh ) {
+
+	var shadowMaterial = new THREE.MeshBasicMaterial( {
+
+		color: 0x000000,
+		transparent: true,
+		opacity: 0.6,
+		depthWrite: false
+
+	} );
+
+	THREE.Mesh.call( this, mesh.geometry, shadowMaterial );
+
+	this.meshMatrix = mesh.matrixWorld;
+
+	this.frustumCulled = false;
+	this.matrixAutoUpdate = false;
+
+};
+
+THREE.ShadowMesh.prototype = Object.create( THREE.Mesh.prototype );
+THREE.ShadowMesh.prototype.constructor = THREE.ShadowMesh;
+
+THREE.ShadowMesh.prototype.update = function () {
+
+	var shadowMatrix = new THREE.Matrix4();
+
+	return function ( plane, lightPosition4D ) {
+
+		// based on https://www.opengl.org/archives/resources/features/StencilTalk/tsld021.htm
+
+		var dot = plane.normal.x * lightPosition4D.x +
+			  plane.normal.y * lightPosition4D.y +
+			  plane.normal.z * lightPosition4D.z +
+			  - plane.constant * lightPosition4D.w;
+
+		var 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 );
+
+	};
+
+}();