var canvas = document.getElementById('canvas');
var scene = new THREE.Scene();
var renderer = new THREE.WebGLRenderer({canvas: canvas, antialias: true});
var camera = new THREE.PerspectiveCamera(45, canvas.clientWidth / canvas.clientWidth, 1, 1000);
var geometry = new THREE.BoxGeometry(50, 50, 50);
var material = new THREE.MeshBasicMaterial({color: '#f00'});
var box = new THREE.Mesh(geometry, material);
scene.add(box);
camera.position.z = 200;
var period = 5;
var clock = new THREE.Clock();
var matrix = new THREE.Matrix4();
render();
function render() {
requestAnimationFrame(render);
if (canvas.width !== canvas.clientWidth || canvas.height !== canvas.clientHeight) {
renderer.setSize(canvas.clientWidth, canvas.clientHeight, false);
camera.aspect = canvas.clientWidth / canvas.clientHeight;
camera.updateProjectionMatrix();
}
matrix.makeRotationY(clock.getDelta() * 2 * Math.PI / period);
camera.position.applyMatrix4(matrix);
camera.lookAt(box.position);
renderer.render(scene, camera);
}