Object3D: Added onBeforeRender callback. See #9662

src/core/Object3D.js

@@ -91,6 +91,8 @@ function Object3D() {
 
 	this.userData = {};
 
+	this.onBeforeRender = null;
+
 }
 
 Object3D.DefaultUp = new Vector3( 0, 1, 0 );

src/renderers/WebGLRenderer.js

@@ -1524,6 +1524,8 @@ function WebGLRenderer( parameters ) {
 
 			} else {
 
+				if ( object.onBeforeRender !== null ) object.onBeforeRender();
+
 				_this.renderBufferDirect( camera, fog, geometry, material, object, group );
 
 			}