【解决方法】
通过获取鼠标位置后，添加监听函数并以加camera的lookUp方法来实现代码如下
if (flags.looking) {
var width = canvas.clientWidth;
var height = canvas.clientHeight;
var x = (mousePosition.x - startMousePosition.x) / width;
var y = -(mousePosition.y - startMousePosition.y) / height;
var lookFactor = 0.05;
camera.lookRight(x * lookFactor);
camera.lookUp(y * lookFactor);
}
