var camera = new THREE.PerspectiveCamera( fov, aspect , near,far );

//透视照相机参数设置
var fov = 45,//拍摄距离 视野角值越大，场景中的物体越小
 near = 1,//相机离视体积最近的距离
 far = 1000,//相机离视体积最远的距离
 aspect = window.innerWidth / window.innerHeight; //纵横比
var camera = new THREE.PerspectiveCamera(fov,aspect, near, far);

//改变fov值，并更新场景的渲染
camera.fov = fov;
camera.updateProjectionMatrix();
renderer.render(scene, camera);
 //updateinfo();

//监听鼠标滚动事件
canvas.addEventListener('mousewheel', mousewheel, false);

//鼠标滑轮-鼠标上下滑轮实现放大缩小效果
function mousewheel(e) {
 e.preventDefault();
 //e.stopPropagation();
 if (e.wheelDelta) { //判断浏览器IE，谷歌滑轮事件
 if (e.wheelDelta > 0) { //当滑轮向上滚动时
  fov -= (near < fov ? 1 : 0);
 }
 if (e.wheelDelta < 0) { //当滑轮向下滚动时
  fov += (fov < far ? 1 : 0);
 }
 } else if (e.detail) { //Firefox滑轮事件
 if (e.detail > 0) { //当滑轮向上滚动时
  fov -= 1;
 }
 if (e.detail < 0) { //当滑轮向下滚动时
  fov += 1;
 }
 }
 //改变fov值，并更新场景的渲染
 camera.fov = fov;
 camera.updateProjectionMatrix();
 renderer.render(scene, camera);
 //updateinfo();
}