// once everything is loaded, we run our Three.js stuff.
    function init() {

        var stopMovingLight = false;

        var stats = initStats();

        // create a scene, that will hold all our elements such as objects, cameras and lights.
        var scene = new THREE.Scene();

        // create a camera, which defines where we're looking at.
        var camera = new THREE.PerspectiveCamera(45, window.innerWidth / window.innerHeight, 0.1, 1000);

        // create a render and set the size
        var renderer = new THREE.WebGLRenderer();

        renderer.setClearColor(new THREE.Color(0xEEEEEE, 1.0));
        renderer.setSize(window.innerWidth, window.innerHeight);
        renderer.shadowMapEnabled = true;
        renderer.shadowMapType = THREE.PCFShadowMap;

        // create the ground plane
        var planeGeometry = new THREE.PlaneGeometry(60, 20, 1, 1);
        var planeMaterial = new THREE.MeshLambertMaterial({color: 0xffffff});
        var plane = new THREE.Mesh(planeGeometry, planeMaterial);
        plane.receiveShadow = true;

        // rotate and position the plane
        plane.rotation.x = -0.5 * Math.PI;
        plane.position.x = 15;
        plane.position.y = 0;
        plane.position.z = 0;

        // add the plane to the scene
        scene.add(plane);

        // create a cube
        var cubeGeometry = new THREE.BoxGeometry(4, 4, 4);
        var cubeMaterial = new THREE.MeshLambertMaterial({color: 0xff3333});
        var cube = new THREE.Mesh(cubeGeometry, cubeMaterial);
        cube.castShadow = true;

        // position the cube
        cube.position.x = -4;
        cube.position.y = 3;
        cube.position.z = 0;

        // add the cube to the scene
        scene.add(cube);

        var sphereGeometry = new THREE.SphereGeometry(4, 20, 20);
        var sphereMaterial = new THREE.MeshLambertMaterial({color: 0x7777ff});
        var sphere = new THREE.Mesh(sphereGeometry, sphereMaterial);

        // position the sphere
        sphere.position.x = 20;
        sphere.position.y = 0;
        sphere.position.z = 2;
        sphere.castShadow = true;

        // add the sphere to the scene
        scene.add(sphere);

        // position and point the camera to the center of the scene
        camera.position.x = -35;
        camera.position.y = 30;
        camera.position.z = 25;
        camera.lookAt(new THREE.Vector3(10, 0, 0));

        // add subtle ambient lighting
        var ambiColor = "#1c1c1c";
        var ambientLight = new THREE.AmbientLight(ambiColor);
        scene.add(ambientLight);

        // add spotlight for a bit of light
        var spotLight0 = new THREE.SpotLight(0xcccccc);
        spotLight0.position.set(-40, 30, -10);
        spotLight0.lookAt(plane);
        scene.add(spotLight0);


        var target = new THREE.Object3D();
        target.position = new THREE.Vector3(5, 0, 0);


        var pointColor = "#ffffff";
        var spotLight = new THREE.SpotLight(pointColor);
        spotLight.position.set(-40, 60, -10);
        spotLight.castShadow = true;
        spotLight.shadowCameraNear = 2;
        spotLight.shadowCameraFar = 200;
        spotLight.shadowCameraFov = 30;
        spotLight.target = plane;
        spotLight.distance = 0;
        spotLight.angle = 0.4;


        scene.add(spotLight);


        // add a small sphere simulating the pointlight
        var sphereLight = new THREE.SphereGeometry(0.2);
        var sphereLightMaterial = new THREE.MeshBasicMaterial({color: 0xac6c25});
        var sphereLightMesh = new THREE.Mesh(sphereLight, sphereLightMaterial);
        sphereLightMesh.castShadow = true;

        sphereLightMesh.position = new THREE.Vector3(3, 20, 3);
        scene.add(sphereLightMesh);


        // add the output of the renderer to the html element
        document.getElementById("WebGL-output").appendChild(renderer.domElement);

        // call the render function
        var step = 0;

        // used to determine the switch point for the light animation
        var invert = 1;
        var phase = 0;

        var controls = new function () {
            this.rotationSpeed = 0.03;
            this.bouncingSpeed = 0.03;
            this.ambientColor = ambiColor;
            this.pointColor = pointColor;
            this.intensity = 1;
            this.distance = 0;
            this.exponent = 30;
            this.angle = 0.1;
            this.debug = false;
            this.castShadow = true;
            this.onlyShadow = false;
            this.target = "Plane";
            this.stopMovingLight = false;

        };

        var gui = new dat.GUI();
        gui.addColor(controls, 'ambientColor').onChange(function (e) {
            ambientLight.color = new THREE.Color(e);
        });

        gui.addColor(controls, 'pointColor').onChange(function (e) {
            spotLight.color = new THREE.Color(e);
        });

        gui.add(controls, 'angle', 0, Math.PI * 2).onChange(function (e) {
            spotLight.angle = e;
        });

        gui.add(controls, 'intensity', 0, 5).onChange(function (e) {
            spotLight.intensity = e;
        });

        gui.add(controls, 'distance', 0, 200).onChange(function (e) {
            spotLight.distance = e;
        });

        gui.add(controls, 'exponent', 0, 100).onChange(function (e) {
            spotLight.exponent = e;
        });

        gui.add(controls, 'debug').onChange(function (e) {
            spotLight.shadowCameraVisible = e;
        });

        gui.add(controls, 'castShadow').onChange(function (e) {
            spotLight.castShadow = e;
        });

        gui.add(controls, 'onlyShadow').onChange(function (e) {
            spotLight.onlyShadow = e;
        });

        gui.add(controls, 'target', ['Plane', 'Sphere', 'Cube']).onChange(function (e) {
            console.log(e);
            switch (e) {
                case "Plane":
                    spotLight.target = plane;
                    break;
                case "Sphere":
                    spotLight.target = sphere;
                    break;
                case "Cube":
                    spotLight.target = cube;
                    break;
            }

        });

        gui.add(controls, 'stopMovingLight').onChange(function (e) {
            stopMovingLight = e;
        });


        render();

        function render() {
            stats.update();
            // rotate the cube around its axes
            cube.rotation.x += controls.rotationSpeed;
            cube.rotation.y += controls.rotationSpeed;
            cube.rotation.z += controls.rotationSpeed;

            // bounce the sphere up and down
            step += controls.bouncingSpeed;
            sphere.position.x = 20 + ( 10 * (Math.cos(step)));
            sphere.position.y = 2 + ( 10 * Math.abs(Math.sin(step)));

            // move the light simulation
            if (!stopMovingLight) {
                if (phase > 2 * Math.PI) {
                    invert = invert * -1;
                    phase -= 2 * Math.PI;
                } else {
                    phase += controls.rotationSpeed;
                }
                sphereLightMesh.position.z = +(7 * (Math.sin(phase)));
                sphereLightMesh.position.x = +(14 * (Math.cos(phase)));
                sphereLightMesh.position.y = 10;

                if (invert < 0) {
                    var pivot = 14;
                    sphereLightMesh.position.x = (invert * (sphereLightMesh.position.x - pivot)) + pivot;
                }

                spotLight.position.copy(sphereLightMesh.position);
            }

            // render using requestAnimationFrame
            requestAnimationFrame(render);


            renderer.render(scene, camera);
        }

        function initStats() {

            var stats = new Stats();

            stats.setMode(0); // 0: fps, 1: ms

            // Align top-left
            stats.domElement.style.position = 'absolute';
            stats.domElement.style.left = '0px';
            stats.domElement.style.top = '0px';

            document.getElementById("Stats-output").appendChild(stats.domElement);

            return stats;
        }
    }

    window.onload = init;