three.js3D视野缩放效果实现方法

//照相机配置
  var fov = 40;//拍摄距离
  var near = 1;//最小范围
  var far = 1000;//最大范围
  var camera = new THREE.PerspectiveCamera(fov, window.innerWidth / window.innerHeight, near, far);

camera.fov = fov;//fov是变量哦 
camera.updateProjectionMatrix();
renderer.render(scene, camera);

canvas.addEventListener('mousewheel', mousewheel, false);
    //鼠标滑轮
    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;
        }
      }
      camera.fov = fov;
      camera.updateProjectionMatrix();
      renderer.render(scene, camera);
      //updateinfo();
    }