如何在easelJS中位图中添加滚动缩放功能？

var stage = new createjs.Stage("canvas");
var bitmap = new createjs.Bitmap("image.jpg");
stage.addChild(bitmap);

stage.enableMouseOver();
stage.mouseMoveOutside = true;

var scale = 1;
var offsetX = 0;
var offsetY = 0;

stage.addEventListener("mousewheel", handleMouseWheel);

function handleMouseWheel(event) {
  var delta = event.deltaY;
  
  // 根据滚轮滚动方向，调整缩放比例
  if (delta > 0) {
    scale *= 0.9; // 缩小
  } else {
    scale *= 1.1; // 放大
  }
  
  // 根据缩放比例调整位图的尺寸
  bitmap.scaleX = bitmap.scaleY = scale;
  
  // 根据缩放比例调整舞台的偏移量，以保持位图的中心位置不变
  offsetX = event.stageX - (event.stageX - offsetX) * scale;
  offsetY = event.stageY - (event.stageY - offsetY) * scale;
  
  // 根据偏移量调整位图的位置
  bitmap.x = offsetX;
  bitmap.y = offsetY;
  
  stage.update();
}

stage.addEventListener("stagemousedown", handleMouseDown);
stage.addEventListener("stagemousemove", handleMouseMove);
stage.addEventListener("stagemouseup", handleMouseUp);

var isDragging = false;
var lastX = 0;
var lastY = 0;

function handleMouseDown(event) {
  isDragging = true;
  lastX = event.stageX;
  lastY = event.stageY;
}

function handleMouseMove(event) {
  if (isDragging) {
    var deltaX = event.stageX - lastX;
    var deltaY = event.stageY - lastY;
    
    // 根据位图的缩放比例调整平移距离
    deltaX /= scale;
    deltaY /= scale;
    
    // 更新舞台的偏移量
    offsetX += deltaX;
    offsetY += deltaY;
    
    // 根据偏移量调整位图的位置
    bitmap.x = offsetX;
    bitmap.y = offsetY;
    
    stage.update();
    
    lastX = event.stageX;
    lastY = event.stageY;
  }
}

function handleMouseUp(event) {
  isDragging = false;
}