Add SceneObserver

src/r3f/utilities/SceneObserver.js

@@ -0,0 +1,98 @@
+import { EventDispatcher } from 'three';
+
+function traverse( root, callback ) {
+
+	if ( callback( root ) ) {
+
+		return;
+
+	}
+
+	root.children.forEach( c => {
+
+		traverse( c, callback );
+
+	} );
+
+}
+class SceneWatcher extends EventDispatcher {
+
+	constructor() {
+
+		super();
+
+		this.objects = new Set();
+		this.observed = new Set();
+		this._addedCallback = ( { child } ) => {
+
+			traverse( child, c => {
+
+				if ( this.observed.has( c ) ) {
+
+					return true;
+
+				} else {
+
+					this.objects.add( c );
+					c.addEventListener( 'childadded', this._addedCallback );
+					c.addEventListener( 'childremoved', this._removedCallback );
+					this.dispatchEvent( { type: 'childadded', child } );
+					return false;
+
+				}
+
+			} );
+
+		};
+
+		this._removedCallback = ( { child } ) => {
+
+			traverse( child, c => {
+
+				if ( this.observed.has( c ) ) {
+
+					return true;
+
+				} else {
+
+					this.objects.delete( c );
+					c.removeEventListener( 'childadded', this._addedCallback );
+					c.removeEventListener( 'childremoved', this._removedCallback );
+					this.dispatchEvent( { type: 'childremoved', child } );
+					return false;
+
+				}
+
+			} );
+
+		};
+
+	}
+
+	observe( root ) {
+
+		const { observed } = this;
+		this._addedCallback( { child: root } );
+		observed.add( root );
+
+	}
+
+	unobserve( root ) {
+
+		const { observed } = this;
+		observed.delete( root );
+		this._removedCallback( { child: root } );
+
+	}
+
+	dispose() {
+
+		this.observed.forEach( root => {
+
+			this.unobserve( root );
+
+		} );
+
+	}
+
+}