Babylon.js/src/Behaviors/Mesh/babylon.multiPointerScaleBehavior.ts

module BABYLON {
    /**
     * A behavior that when attached to a mesh will allow the mesh to be scaled
     */
    export class MultiPointerScaleBehavior implements Behavior<Mesh> {
        private _dragBehaviorA:PointerDragBehavior;
        private _dragBehaviorB:PointerDragBehavior;
        private _startDistance = 0;
        private _initialScale = new Vector3(0,0,0);
        private _targetScale = new Vector3(0,0,0);
        private _ownerNode:Mesh;
        private _sceneRenderObserver:Nullable<Observer<Scene>> = null;

        constructor(){
            this._dragBehaviorA = new BABYLON.PointerDragBehavior({});
            this._dragBehaviorA.moveAttached = false;
            this._dragBehaviorB = new BABYLON.PointerDragBehavior({});
            this._dragBehaviorB.moveAttached = false;
        }
        
        /**
         *  The name of the behavior
         */
        public get name(): string {
            return "MultiPointerScale";
        }

        /**
         *  Initializes the behavior
         */
        public init() {}

        private _getCurrentDistance(){
            return this._dragBehaviorA.lastDragPosition.subtract(this._dragBehaviorB.lastDragPosition).length();
        }

        /**
         * Attaches the scale behavior the passed in mesh
         * @param ownerNode The mesh that will be scaled around once attached
         */
        public attach(ownerNode: Mesh): void {
            this._ownerNode = ownerNode;

            // Create 2 drag behaviors such that each will only be triggered by a separate pointer
            this._dragBehaviorA.onDragStartObservable.add((e)=>{
                if(this._dragBehaviorA.dragging && this._dragBehaviorB.dragging){
                    if(this._dragBehaviorA.currentDraggingPointerID == this._dragBehaviorB.currentDraggingPointerID){
                        this._dragBehaviorA.releaseDrag();
                    }else{
                        this._initialScale.copyFrom(ownerNode.scaling)
                        this._startDistance = this._getCurrentDistance();
                    }
                }
            });
            this._dragBehaviorB.onDragStartObservable.add((e)=>{
                if(this._dragBehaviorA.dragging && this._dragBehaviorB.dragging){
                    if(this._dragBehaviorA.currentDraggingPointerID == this._dragBehaviorB.currentDraggingPointerID){
                        this._dragBehaviorB.releaseDrag();
                    }else{
                        this._initialScale.copyFrom(ownerNode.scaling)
                        this._startDistance = this._getCurrentDistance();
                    }
                }
            });

            // Once both drag behaviors are active scale based on the distance between the two pointers
            [this._dragBehaviorA, this._dragBehaviorB].forEach((behavior)=>{
                behavior.onDragObservable.add(()=>{
                    if(this._dragBehaviorA.dragging && this._dragBehaviorB.dragging){
                        var ratio = this._getCurrentDistance()/this._startDistance;
                        this._initialScale.scaleToRef(ratio, this._targetScale);
                    }
                });
            })

            ownerNode.addBehavior(this._dragBehaviorA);
            ownerNode.addBehavior(this._dragBehaviorB);

            // On every frame move towards target scaling to avoid jitter caused by vr controllers
            this._sceneRenderObserver = ownerNode.getScene().onBeforeRenderObservable.add(()=>{
                if(this._dragBehaviorA.dragging && this._dragBehaviorB.dragging){
                    var change = this._targetScale.subtract(ownerNode.scaling).scaleInPlace(0.1);
                    if(change.length()>0.01){
                        ownerNode.scaling.addInPlace(change);
                    }
                }
            });
        }
        /**
         *  Detaches the behavior from the mesh
         */
        public detach(): void {
            this._ownerNode.getScene().onBeforeRenderObservable.remove(this._sceneRenderObserver);
            [this._dragBehaviorA, this._dragBehaviorB].forEach((behavior)=>{
                behavior.onDragStartObservable.clear();
                behavior.onDragObservable.clear();
                this._ownerNode.removeBehavior(behavior);
            });
        }
    }
}