CreateJS : how to limit the movement of my clip to the size of my scene?

Hello!

I have a zoom system that works by scrolling the mouse. I would like however, that when I move in the zoom, the area is limited to the size of my scene.

Currently, I can bring out my image of the canas ...

I drew a rectangle of 1920/1080. So I want the image doesn't exceed this area.

The code and the demo online

//Référence du scénario
_this = this;
// Add a background
var bg = new createjs.Shape();
bg.graphics.beginStroke("#000");
bg.graphics.beginFill("#222");
bg.graphics.setStrokeStyle(1);
bg.graphics.drawRect(0, 0, 1920, 1080);
bg.alpha=0.5;
bg.setBounds(0, 0, 1920, 1080);
var bounds = bg.getBounds();
stage.addChild(bg);
//Mouse cursor
stage.enableMouseOver();
var dragStart = null;
//Gestion du touché sur tablette/mobile
createjs.Touch.enable(stage);
createjs.Ticker.addEventListener("tick", onTick);
stage.addEventListener('mousedown', onMouseDown);
stage.addEventListener('stagemousemove', onMouseMove);
stage.addEventListener('stagemouseup', onMouseUp);
stage.addEventListener('mouseleave', onMouseUp);
canvas.addEventListener('DOMMouseScroll', onMouseWheel, false);
canvas.addEventListener('mousewheel', onMouseWheel, false);
function zoom(delta){
        var p = _this.test.globalToLocal(stage.mouseX, stage.mouseY);
        var scale = Math.max(1, Math.min(_this.test.scaleX + delta, 2));
       _this.test.scaleX = _this.test.scaleY = scale;
        var p2 = _this.test.globalToLocal(stage.mouseX, stage.mouseY);
        if(_this.test.rotation == 0){
            _this.test.x += (p2.x - p.x) * scale;
            _this.test.y += (p2.y - p.y) * scale;
        }else if (_this.test.rotation == 90){
            _this.test.x -= (p2.y - p.y) * (scale);
            _this.test.y += (p2.x - p.x) * (scale);
        }else if(test.rotation == 180){
            _this.test.x -= (p2.x - p.x) * scale;
            _this.test.y -= (p2.y - p.y) * scale;
        }else{
            _this.test.x += (p2.y - p.y) * (scale);
            _this.test.y -= (p2.x - p.x) * (scale);
        }
    }
    function rotate(r){
        if((_this.test.rotation+r)  > 270){
            _this.test.rotation = 0;
        }else{
            _this.test.rotation += r;
        }
    }
function onMouseDown(){
  dragStart = new createjs.Point(stage.mouseX, stage.mouseY);
}
function onMouseMove(evt){
  if (dragStart){
    var mouse = new createjs.Point(stage.mouseX, stage.mouseY);
    var delta = new createjs.Point(mouse.x - dragStart.x, mouse.y - dragStart.y);
    dragStart = mouse;
    _this.test.x += delta.x;
    _this.test.y += delta.y;
  }
}
function onMouseUp(){
  dragStart = null;
}
function onMouseWheel(e){
  var delta = e.wheelDelta ? e.wheelDelta/100 : e.detail ? -e.detail : 0;
  if (delta) zoom(delta);
  return e.preventDefault() && false;
}
function onTick(){
  stage.update();
}

Thanks!

Matt