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

        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 webGLRenderer = new THREE.WebGLRenderer();
        webGLRenderer.setClearColor(new THREE.Color(0x000000, 1.0));
        webGLRenderer.setSize(window.innerWidth, window.innerHeight);
        webGLRenderer.shadowMapEnabled = true;


        // position and point the camera to the center of the scene
        camera.position.x = -30;
        camera.position.y = 40;
        camera.position.z = 50;
        camera.lookAt(new THREE.Vector3(10, 0, 0));

        // add the output of the renderer to the html element
        $("#WebGL-output").append(webGLRenderer.domElement);

        // call the render function
        var step = 0;

        var knot;

        // setup the control gui
        var controls = new function () {
            // we need the first child, since it's a multimaterial
            this.radius = 40;
            this.tube = 28.2;
            this.radialSegments = 600;
            this.tubularSegments = 12;
            this.p = 5;
            this.q = 4;
            this.heightScale = 4;
            this.asParticles = true;
            this.rotate = true;

            this.redraw = function () {
                // remove the old plane
                if (knot) scene.remove(knot);
                // create a new one
                var geom = new THREE.TorusKnotGeometry(controls.radius, controls.tube, Math.round(controls.radialSegments), Math.round(controls.tubularSegments), Math.round(controls.p), Math.round(controls.q), controls.heightScale);

                if (controls.asParticles) {
                    knot = createParticleSystem(geom);
                } else {
                    knot = createMesh(geom);
                }

                // add it to the scene.
                scene.add(knot);
            };

        }

        var gui = new dat.GUI();
        gui.add(controls, 'radius', 0, 40).onChange(controls.redraw);
        gui.add(controls, 'tube', 0, 40).onChange(controls.redraw);
        gui.add(controls, 'radialSegments', 0, 400).step(1).onChange(controls.redraw);
        gui.add(controls, 'tubularSegments', 1, 20).step(1).onChange(controls.redraw);
        gui.add(controls, 'p', 1, 10).step(1).onChange(controls.redraw);
        gui.add(controls, 'q', 1, 15).step(1).onChange(controls.redraw);
        gui.add(controls, 'heightScale', 0, 5).onChange(controls.redraw);
        gui.add(controls, 'asParticles').onChange(controls.redraw);
        gui.add(controls, 'rotate').onChange(controls.redraw);
      
        gui.close();

        controls.redraw();

        render();

        // from THREE.js examples
        function generateSprite() {

            var canvas = document.createElement('canvas');
            canvas.width = 16;
            canvas.height = 16;

            var context = canvas.getContext('2d');
            var gradient = context.createRadialGradient(canvas.width / 2, canvas.height / 2, 0, canvas.width / 2, canvas.height / 2, canvas.width / 2);
            gradient.addColorStop(0, 'rgba(255,255,255,1)');
            gradient.addColorStop(0.2, 'rgba(0,255,255,1)');
            gradient.addColorStop(0.4, 'rgba(0,0,64,1)');
            gradient.addColorStop(1, 'rgba(0,0,0,1)');

            context.fillStyle = gradient;
            context.fillRect(0, 0, canvas.width, canvas.height);

            var texture = new THREE.Texture(canvas);
            texture.needsUpdate = true;
            return texture;

        }

        function createParticleSystem(geom) {
            var material = new THREE.ParticleBasicMaterial({
                color: 0xffffff,
                size: 3,
                transparent: true,
                blending: THREE.AdditiveBlending,
                map: generateSprite()
            });

            var system = new THREE.ParticleSystem(geom, material);
            system.sortParticles = true;
            return system;
        }

        function createMesh(geom) {

            // assign two materials
            var meshMaterial = new THREE.MeshNormalMaterial({});
            meshMaterial.side = THREE.DoubleSide;

            // create a multimaterial
            var mesh = THREE.SceneUtils.createMultiMaterialObject(geom, [meshMaterial]);

            return mesh;
        }

        function render() {
            stats.update();

            if (controls.rotate) {
                knot.rotation.y = step += 0.01;
            }

            // render using requestAnimationFrame
            requestAnimationFrame(render);
            webGLRenderer.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';

            $("#Stats-output").append(stats.domElement);

            return stats;
        }
    });