(function() {

    var _isBrowser = typeof window !== 'undefined',
        Matter = _isBrowser ? window.Matter : require('../../build/matter-dev.js');
        
    var Demo = {};
    Matter.Demo = Demo;

    if (!_isBrowser) {
        module.exports = Demo;
    }

    // Matter aliases
    var Engine = Matter.Engine,
        World = Matter.World,
        Bodies = Matter.Bodies,
        Body = Matter.Body,
        Composite = Matter.Composite,
        Composites = Matter.Composites,
        Common = Matter.Common,
        Constraint = Matter.Constraint,
        Events = Matter.Events,
        Bounds = Matter.Bounds,
        Vector = Matter.Vector,
        Vertices = Matter.Vertices,
        MouseConstraint = Matter.MouseConstraint,
        Mouse = Matter.Mouse,
        Query = Matter.Query,
        Svg = Matter.Svg;

    // MatterTools aliases
    if (_isBrowser && window.MatterTools) {
        var Gui = MatterTools.Gui,
            Inspector = MatterTools.Inspector;
    }

    var _engine,
        _runner,
        _gui,
        _inspector,
        _sceneName,
        _mouseConstraint,
        _sceneEvents = [],
        _useInspector = _isBrowser && window.location.hash.indexOf('-inspect') !== -1,
        _isMobile = _isBrowser && /(ipad|iphone|ipod|android)/gi.test(navigator.userAgent),
        _isAutomatedTest = _isBrowser ? false : true;
    
    // initialise the demo

    Demo.init = function() {
        // some example engine options
        var options = {
            positionIterations: 6,
            velocityIterations: 4,
            enableSleeping: false,
            metrics: { extended: true }
        };

        // create a Matter engine
        // NOTE: this is actually Matter.Engine.create(), see the aliases at top of this file
        if (_isBrowser) {
            var container = document.getElementById('canvas-container');
            _engine = Engine.create(container, options);

            // add a mouse controlled constraint
            _mouseConstraint = MouseConstraint.create(_engine);
            World.add(_engine.world, _mouseConstraint);
        } else {
            _engine = Engine.create(options);
            _engine.render = {};
            _engine.render.options = {};
        }

        // engine reference for external use
        Matter.Demo._engine = _engine;

        // skip runner when performing automated tests
        if (_isAutomatedTest) return;

        // run the engine
        _runner = Engine.run(_engine);

        // default scene function name
        _sceneName = 'mixed';
        
        // get the scene function name from hash
        if (window.location.hash.length !== 0) 
            _sceneName = window.location.hash.replace('#', '').replace('-inspect', '');

        // set up a scene with bodies
        Demo[_sceneName]();

        // set up demo interface (see end of this file)
        Demo.initControls();
    };

    // call init when the page has loaded fully

    if (_isBrowser) {
        if (window.addEventListener) {
            window.addEventListener('load', Demo.init);
        } else if (window.attachEvent) {
            window.attachEvent('load', Demo.init);
        }
    }

    // each demo scene is set up in its own function, see below

    Demo.mixed = function() {
        var _world = _engine.world;

        Demo.reset();

        var stack = Composites.stack(20, 20, 15, 4, 0, 0, function(x, y, column, row) {
            var sides = Math.round(Common.random(1, 8));

            // triangles can be a little unstable, so avoid until fixed
            sides = (sides === 3) ? 4 : sides;

            // round the edges of some bodies
            var chamfer = null;
            if (sides > 2 && Common.random() > 0.7) {
                chamfer = {
                    radius: 10
                };
            }

            switch (Math.round(Common.random(0, 1))) {
            case 0:
                if (Common.random() < 0.8) {
                    return Bodies.rectangle(x, y, Common.random(25, 50), Common.random(25, 50), { chamfer: chamfer });
                } else {
                    return Bodies.rectangle(x, y, Common.random(80, 120), Common.random(25, 30), { chamfer: chamfer });
                }
                break;
            case 1:
                return Bodies.polygon(x, y, sides, Common.random(25, 50), { chamfer: chamfer });
            }
        });

        World.add(_world, stack);
        
        var renderOptions = _engine.render.options;
    };

    Demo.compound = function() {
        var _world = _engine.world;

        Demo.reset();

        var size = 200,
            x = 200,
            y = 200,
            partA = Bodies.rectangle(x, y, size, size / 5),
            partB = Bodies.rectangle(x, y, size / 5, size, { render: partA.render });

        var compoundBodyA = Body.create({
            parts: [partA, partB]
        });

        size = 150;
        x = 400;
        y = 300;

        var partC = Bodies.circle(x, y, 30),
            partD = Bodies.circle(x + size, y, 30),
            partE = Bodies.circle(x + size, y + size, 30),
            partF = Bodies.circle(x, y + size, 30);

        var compoundBodyB = Body.create({
            parts: [partC, partD, partE, partF]
        });

        var constraint = Constraint.create({
            pointA: { x: 400, y: 100 },
            bodyB: compoundBodyB,
            pointB: { x: 0, y: -50 }
        });

        World.add(_world, [compoundBodyA, compoundBodyB, constraint]);
        
        var renderOptions = _engine.render.options;
        renderOptions.showAxes = true;
        renderOptions.showPositions = true;
        renderOptions.showConvexHulls = true;
    };

    Demo.compoundStack = function() {
        var _world = _engine.world;

        Demo.reset();

        var size = 50;

        var stack = Composites.stack(100, 220, 12, 6, 0, 0, function(x, y, column, row) {
            var partA = Bodies.rectangle(x, y, size, size / 5),
                partB = Bodies.rectangle(x, y, size / 5, size, { render: partA.render });

            return Body.create({
                parts: [partA, partB]
            });
        });

        World.add(_world, stack);
    };

    Demo.concave = function() {
        var _world = _engine.world;

        Demo.reset();

        var arrow = Vertices.fromPath('40 0 40 20 100 20 100 80 40 80 40 100 0 50'),
            chevron = Vertices.fromPath('100 0 75 50 100 100 25 100 0 50 25 0'),
            star = Vertices.fromPath('50 0 63 38 100 38 69 59 82 100 50 75 18 100 31 59 0 38 37 38'),
            horseShoe = Vertices.fromPath('35 7 19 17 14 38 14 58 25 79 45 85 65 84 65 66 46 67 34 59 30 44 33 29 45 23 66 23 66 7 53 7');

        var stack = Composites.stack(50, 50, 6, 4, 10, 10, function(x, y, column, row) {
            var color = Common.choose(['#556270', '#4ECDC4', '#C7F464', '#FF6B6B', '#C44D58']);
            return Bodies.fromVertices(x, y, Common.choose([arrow, chevron, star, horseShoe]), {
                render: {
                    fillStyle: color,
                    strokeStyle: color
                }
            }, true);
        });

        World.add(_world, stack);

        var renderOptions = _engine.render.options;
        renderOptions.showAngleIndicator = false;
    };

    Demo.svg = function() {
        var _world = _engine.world;

        Demo.reset();

        var svgs = [
            'iconmonstr-check-mark-8-icon', 
            'iconmonstr-paperclip-2-icon',
            'iconmonstr-puzzle-icon',
            'iconmonstr-user-icon'
        ];

        for (var i = 0; i < svgs.length; i += 1) {
            (function(i) {
                $.get('./svg/' + svgs[i] + '.svg').done(function(data) {
                    var vertexSets = [],
                        color = Common.choose(['#556270', '#4ECDC4', '#C7F464', '#FF6B6B', '#C44D58']);

                    $(data).find('path').each(function(i, path) {
                        var points = Svg.pathToVertices(path, 30);
                        vertexSets.push(Vertices.scale(points, 0.4, 0.4));
                    });

                    World.add(_world, Bodies.fromVertices(100 + i * 150, 200 + i * 50, vertexSets, {
                        render: {
                            fillStyle: color,
                            strokeStyle: color
                        }
                    }, true));
                });
            })(i);
        }

        $.get('./svg/svg.svg').done(function(data) {
            var vertexSets = [],
                color = Common.choose(['#556270', '#4ECDC4', '#C7F464', '#FF6B6B', '#C44D58']);

            $(data).find('path').each(function(i, path) {
                vertexSets.push(Svg.pathToVertices(path, 30));
            });

            World.add(_world, Bodies.fromVertices(400, 80, vertexSets, {
                render: {
                    fillStyle: color,
                    strokeStyle: color
                }
            }, true));
        });

        var renderOptions = _engine.render.options;
        renderOptions.showAngleIndicator = false;
    };

    Demo.terrain = function() {
        var _world = _engine.world;

        Demo.reset();
        _world.bodies = [];

        var terrain;

        $.get('./svg/terrain.svg').done(function(data) {
            var vertexSets = [],
                color = Common.choose(['#556270', '#4ECDC4', '#C7F464', '#FF6B6B', '#C44D58']);

            $(data).find('path').each(function(i, path) {
                vertexSets.push(Svg.pathToVertices(path, 30));
            });

            terrain = Bodies.fromVertices(400, 350, vertexSets, {
                isStatic: true,
                render: {
                    fillStyle: color,
                    strokeStyle: color
                }
            }, true);

            World.add(_world, terrain);

            var bodyOptions = {
                frictionAir: 0, 
                friction: 0.0001,
                restitution: 0.6
            };
            
            World.add(_world, Composites.stack(80, 100, 20, 20, 10, 10, function(x, y, column, row) {
                if (Query.point([terrain], { x: x, y: y }).length === 0) {
                    return Bodies.polygon(x, y, 5, 12, bodyOptions);
                }
            }));
        });

        var renderOptions = _engine.render.options;
        renderOptions.showAngleIndicator = false;
        renderOptions.showVelocity = true;
    };

    Demo.slingshot = function() {
        var _world = _engine.world;

        Demo.reset();
        _world.bodies = [];

        var ground = Bodies.rectangle(395, 600, 815, 50, { isStatic: true, render: { visible: false } }),
            rockOptions = { density: 0.004, render: { sprite: { texture: './img/rock.png' } } },
            rock = Bodies.polygon(170, 450, 8, 20, rockOptions),
            anchor = { x: 170, y: 450 },
            elastic = Constraint.create({ 
                pointA: anchor, 
                bodyB: rock, 
                stiffness: 0.05, 
                render: { 
                    lineWidth: 5, 
                    strokeStyle: '#dfa417' 
                } 
            });

        var pyramid = Composites.pyramid(500, 300, 9, 10, 0, 0, function(x, y, column, row) {
            var texture = column % 2 === 0 ? './img/block.png' : './img/block-2.png';
            return Bodies.rectangle(x, y, 25, 40, { render: { sprite: { texture: texture } } });
        });

        var ground2 = Bodies.rectangle(610, 250, 200, 20, { 
            isStatic: true, 
            render: { 
                fillStyle: '#edc51e', 
                strokeStyle: '#b5a91c' 
            } 
        });

        var pyramid2 = Composites.pyramid(550, 0, 5, 10, 0, 0, function(x, y, column, row) {
            var texture = column % 2 === 0 ? './img/block.png' : './img/block-2.png';
            return Bodies.rectangle(x, y, 25, 40, { render: { sprite: { texture: texture } } });
        });

        World.add(_engine.world, [ground, pyramid, ground2, pyramid2, rock, elastic]);

        Events.on(_engine, 'afterUpdate', function() {
            if (_mouseConstraint.mouse.button === -1 && (rock.position.x > 190 || rock.position.y < 430)) {
                rock = Bodies.polygon(170, 450, 7, 20, rockOptions);
                World.add(_engine.world, rock);
                elastic.bodyB = rock;
            }
        });
        
        var renderOptions = _engine.render.options;
        renderOptions.wireframes = false;
        renderOptions.showAngleIndicator = false;
        renderOptions.background = './img/background.png';
    };

    Demo.rounded = function() {
        var _world = _engine.world;

        Demo.reset();

        World.add(_world, [
            Bodies.rectangle(200, 200, 100, 100, { 
                chamfer: { radius: 20 }
            }),

            Bodies.rectangle(300, 200, 100, 100, { 
                chamfer: { radius: [90, 0, 0, 0] }
            }),

            Bodies.rectangle(400, 200, 200, 200, { 
                chamfer: { radius: [150, 20, 40, 20] }
            }),

            Bodies.rectangle(200, 200, 200, 200, { 
                chamfer: { radius: [150, 20, 150, 20] }
            }),

            Bodies.rectangle(300, 200, 200, 50, { 
                chamfer: { radius: [25, 25, 0, 0] }
            }),

            Bodies.polygon(200, 100, 8, 80, { 
                chamfer: { radius: 30 }
            }),

            Bodies.polygon(300, 100, 5, 80, { 
                chamfer: { radius: [10, 40, 20, 40, 10] }
            }),

            Bodies.polygon(400, 200, 3, 50, { 
                chamfer: { radius: [20, 0, 20] }
            })
        ]);

        var renderOptions = _engine.render.options;
        renderOptions.showAxes = true;
        renderOptions.showCollisions = true;
    };

    Demo.manipulation = function() {
        var _world = _engine.world;

        Demo.reset();

        var bodyA = Bodies.rectangle(100, 200, 50, 50, { isStatic: true }),
            bodyB = Bodies.rectangle(200, 200, 50, 50),
            bodyC = Bodies.rectangle(300, 200, 50, 50),
            bodyD = Bodies.rectangle(400, 200, 50, 50),
            bodyE = Bodies.rectangle(550, 200, 50, 50),
            bodyF = Bodies.rectangle(700, 200, 50, 50),
            bodyG = Bodies.circle(400, 100, 25),
            partA = Bodies.rectangle(600, 200, 120, 50),
            partB = Bodies.rectangle(660, 200, 50, 190),
            compound = Body.create({
                parts: [partA, partB],
                isStatic: true
            });

        World.add(_world, [bodyA, bodyB, bodyC, bodyD, bodyE, bodyF, bodyG, compound]);

        var counter = 0,
            scaleFactor = 1.01;

        _sceneEvents.push(
            Events.on(_engine, 'beforeUpdate', function(event) {
                counter += 1;

                if (counter === 40)
                    Body.setStatic(bodyG, true);

                if (scaleFactor > 1) {
                    Body.scale(bodyF, scaleFactor, scaleFactor);
                    Body.scale(compound, 0.995, 0.995);

                    // modify bodyE vertices
                    bodyE.vertices[0].x -= 0.2;
                    bodyE.vertices[0].y -= 0.2;
                    bodyE.vertices[1].x += 0.2;
                    bodyE.vertices[1].y -= 0.2;
                    Body.setVertices(bodyE, bodyE.vertices);
                }

                // make bodyA move up and down
                // body is static so must manually update velocity for friction to work
                var py = 300 + 100 * Math.sin(_engine.timing.timestamp * 0.002);
                Body.setVelocity(bodyA, { x: 0, y: py - bodyA.position.y });
                Body.setPosition(bodyA, { x: 100, y: py });

                // make compound body move up and down and rotate constantly
                Body.setVelocity(compound, { x: 0, y: py - compound.position.y });
                Body.setAngularVelocity(compound, 0.02);
                Body.setPosition(compound, { x: 600, y: py });
                Body.rotate(compound, 0.02);

                // every 1.5 sec
                if (counter >= 60 * 1.5) {
                    Body.setVelocity(bodyB, { x: 0, y: -10 });
                    Body.setAngle(bodyC, -Math.PI * 0.26);
                    Body.setAngularVelocity(bodyD, 0.2);

                    // reset counter
                    counter = 0;
                    scaleFactor = 1;
                }
            })
        );

        var renderOptions = _engine.render.options;
        renderOptions.showAxes = true;
        renderOptions.showCollisions = true;
        renderOptions.showPositions = true;
        renderOptions.showConvexHulls = true;
    };

    Demo.compositeManipulation = function() {
        var _world = _engine.world;

        Demo.reset();

        var stack = Composites.stack(200, 200, 4, 4, 0, 0, function(x, y, column, row) {
            return Bodies.rectangle(x, y, 40, 40);
        });

        World.add(_world, stack);

        _world.gravity.y = 0;

        _sceneEvents.push(
            Events.on(_engine, 'afterUpdate', function(event) {
                var time = _engine.timing.timestamp;

                Composite.translate(stack, {
                    x: Math.sin(time * 0.001) * 2,
                    y: 0
                });

                Composite.rotate(stack, Math.sin(time * 0.001) * 0.01, {
                    x: 300,
                    y: 300
                });

                var scale = 1 + (Math.sin(time * 0.001) * 0.01);

                Composite.scale(stack, scale, scale, {
                    x: 300,
                    y: 300
                });
            })
        );

        var renderOptions = _engine.render.options;
        renderOptions.wireframes = false;
        renderOptions.showAxes = true;
        renderOptions.showCollisions = true;
    };

    Demo.views = function() {
        var _world = _engine.world;
        
        Demo.reset();
        
        var stack = Composites.stack(20, 20, 15, 4, 0, 0, function(x, y, column, row) {
            switch (Math.round(Common.random(0, 1))) {

            case 0:
                if (Common.random() < 0.8) {
                    return Bodies.rectangle(x, y, Common.random(20, 50), Common.random(20, 50));
                } else {
                    return Bodies.rectangle(x, y, Common.random(80, 120), Common.random(20, 30));
                }
                break;
            case 1:
                var sides = Math.round(Common.random(1, 8));
                sides = (sides === 3) ? 4 : sides;
                return Bodies.polygon(x, y, sides, Common.random(20, 50));
            }
        });
        
        World.add(_world, stack);

        // get the centre of the viewport
        var viewportCentre = {
            x: _engine.render.options.width * 0.5,
            y: _engine.render.options.height * 0.5
        };

        // make the world bounds a little bigger than the render bounds
        _world.bounds.min.x = -300;
        _world.bounds.min.y = -300;
        _world.bounds.max.x = 1100;
        _world.bounds.max.y = 900;

        // keep track of current bounds scale (view zoom)
        var boundsScaleTarget = 1,
            boundsScale = {
                x: 1,
                y: 1
            };

        // use the engine tick event to control our view
        _sceneEvents.push(
            Events.on(_engine, 'beforeTick', function() {
                var world = _engine.world,
                    mouse = _mouseConstraint.mouse,
                    render = _engine.render,
                    translate;

                // mouse wheel controls zoom
                var scaleFactor = mouse.wheelDelta * -0.1;
                if (scaleFactor !== 0) {
                    if ((scaleFactor < 0 && boundsScale.x >= 0.6) || (scaleFactor > 0 && boundsScale.x <= 1.4)) {
                        boundsScaleTarget += scaleFactor;
                    }
                }

                // if scale has changed
                if (Math.abs(boundsScale.x - boundsScaleTarget) > 0.01) {
                    // smoothly tween scale factor
                    scaleFactor = (boundsScaleTarget - boundsScale.x) * 0.2;
                    boundsScale.x += scaleFactor;
                    boundsScale.y += scaleFactor;

                    // scale the render bounds
                    render.bounds.max.x = render.bounds.min.x + render.options.width * boundsScale.x;
                    render.bounds.max.y = render.bounds.min.y + render.options.height * boundsScale.y;

                    // translate so zoom is from centre of view
                    translate = {
                        x: render.options.width * scaleFactor * -0.5,
                        y: render.options.height * scaleFactor * -0.5
                    };

                    Bounds.translate(render.bounds, translate);

                    // update mouse
                    Mouse.setScale(mouse, boundsScale);
                    Mouse.setOffset(mouse, render.bounds.min);
                }

                // get vector from mouse relative to centre of viewport
                var deltaCentre = Vector.sub(mouse.absolute, viewportCentre),
                    centreDist = Vector.magnitude(deltaCentre);

                // translate the view if mouse has moved over 50px from the centre of viewport
                if (centreDist > 50) {
                    // create a vector to translate the view, allowing the user to control view speed
                    var direction = Vector.normalise(deltaCentre),
                        speed = Math.min(10, Math.pow(centreDist - 50, 2) * 0.0002);

                    translate = Vector.mult(direction, speed);

                    // prevent the view moving outside the world bounds
                    if (render.bounds.min.x + translate.x < world.bounds.min.x)
                        translate.x = world.bounds.min.x - render.bounds.min.x;

                    if (render.bounds.max.x + translate.x > world.bounds.max.x)
                        translate.x = world.bounds.max.x - render.bounds.max.x;

                    if (render.bounds.min.y + translate.y < world.bounds.min.y)
                        translate.y = world.bounds.min.y - render.bounds.min.y;

                    if (render.bounds.max.y + translate.y > world.bounds.max.y)
                        translate.y = world.bounds.max.y - render.bounds.max.y;

                    // move the view
                    Bounds.translate(render.bounds, translate);

                    // we must update the mouse too
                    Mouse.setOffset(mouse, render.bounds.min);
                }
            })
        );

        // must enable renderOptions.hasBounds for views to work
        var renderOptions = _engine.render.options;
        renderOptions.hasBounds = true;
    };

    Demo.mixedSolid = function() {
        var _world = _engine.world;
        
        Demo.reset();
        
        var stack = Composites.stack(50, 50, 12, 3, 0, 0, function(x, y, column, row) {
            switch (Math.round(Common.random(0, 1))) {

            case 0:
                if (Common.random() < 0.8) {
                    return Bodies.rectangle(x, y, Common.random(20, 50), Common.random(20, 50));
                } else {
                    return Bodies.rectangle(x, y, Common.random(80, 120), Common.random(20, 30));
                }
                break;
            case 1:
                return Bodies.polygon(x, y, Math.round(Common.random(1, 8)), Common.random(20, 50));

            }
        });
        
        World.add(_world, stack);
        
        var renderOptions = _engine.render.options;
        renderOptions.wireframes = false;
        renderOptions.showAngleIndicator = false;

        if (window.chrome)
            renderOptions.showShadows = true;
    };
    
    Demo.chains = function() {
        var _world = _engine.world,
            group = Body.nextGroup(true);
        
        Demo.reset();
         
        var ropeA = Composites.stack(200, 100, 5, 2, 10, 10, function(x, y, column, row) {
            return Bodies.rectangle(x, y, 50, 20, { collisionFilter: { group: group } });
        });
        
        Composites.chain(ropeA, 0.5, 0, -0.5, 0, { stiffness: 0.8, length: 2 });
        Composite.add(ropeA, Constraint.create({ 
            bodyB: ropeA.bodies[0],
            pointB: { x: -25, y: 0 },
            pointA: { x: 200, y: 100 },
            stiffness: 0.5
        }));
        
        World.add(_world, ropeA);
        
        group = Body.nextGroup(true);
        
        var ropeB = Composites.stack(500, 100, 5, 2, 10, 10, function(x, y, column, row) {
            return Bodies.circle(x, y, 20, { collisionFilter: { group: group } });
        });
        
        Composites.chain(ropeB, 0.5, 0, -0.5, 0, { stiffness: 0.8, length: 2 });
        Composite.add(ropeB, Constraint.create({ 
            bodyB: ropeB.bodies[0],
            pointB: { x: -20, y: 0 },
            pointA: { x: 500, y: 100 },
            stiffness: 0.5
        }));
        
        World.add(_world, ropeB);
    };

    Demo.bridge = function() {
        var _world = _engine.world,
            group = Body.nextGroup(true);
        
        Demo.reset();
         
        var bridge = Composites.stack(150, 300, 9, 1, 10, 10, function(x, y, column, row) {
            return Bodies.rectangle(x, y, 50, 20, { collisionFilter: { group: group } });
        });
        
        Composites.chain(bridge, 0.5, 0, -0.5, 0, { stiffness: 0.9 });
        
        var stack = Composites.stack(200, 40, 6, 3, 0, 0, function(x, y, column, row) {
            return Bodies.polygon(x, y, Math.round(Common.random(1, 8)), Common.random(20, 40));
        });

        World.add(_world, [
            bridge,
            Bodies.rectangle(80, 440, 120, 280, { isStatic: true }),
            Bodies.rectangle(720, 440, 120, 280, { isStatic: true }),
            Constraint.create({ pointA: { x: 140, y: 300 }, bodyB: bridge.bodies[0], pointB: { x: -25, y: 0 } }),
            Constraint.create({ pointA: { x: 660, y: 300 }, bodyB: bridge.bodies[8], pointB: { x: 25, y: 0 } }),
            stack
        ]);
    };
    
    Demo.car = function() {
        var _world = _engine.world,
            scale;
        
        Demo.reset();
        
        scale = 0.9;
        World.add(_world, Composites.car(150, 100, 100 * scale, 40 * scale, 30 * scale));
        
        scale = 0.8;
        World.add(_world, Composites.car(350, 300, 100 * scale, 40 * scale, 30 * scale));
        
        World.add(_world, [
            Bodies.rectangle(200, 150, 650, 20, { isStatic: true, angle: Math.PI * 0.06 }),
            Bodies.rectangle(500, 350, 650, 20, { isStatic: true, angle: -Math.PI * 0.06 }),
            Bodies.rectangle(340, 580, 700, 20, { isStatic: true, angle: Math.PI * 0.04 })
        ]);
        
        var renderOptions = _engine.render.options;
        renderOptions.showAngleIndicator = true;
        renderOptions.showCollisions = true;
    };

    Demo.friction = function() {
        var _world = _engine.world;
        
        Demo.reset();
        
        World.add(_world, [
            Bodies.rectangle(300, 180, 700, 20, { isStatic: true, angle: Math.PI * 0.06 }),
            Bodies.rectangle(300, 70, 40, 40, { friction: 0.001 })
        ]);

        World.add(_world, [
            Bodies.rectangle(300, 350, 700, 20, { isStatic: true, angle: Math.PI * 0.06 }),
            Bodies.rectangle(300, 250, 40, 40, { friction: 0.0005 })
        ]);

        World.add(_world, [
            Bodies.rectangle(300, 520, 700, 20, { isStatic: true, angle: Math.PI * 0.06 }),
            Bodies.rectangle(300, 430, 40, 40, { friction: 0 })
        ]);

        var renderOptions = _engine.render.options;
        renderOptions.showAngleIndicator = false;
        renderOptions.showVelocity = true;
    };

    Demo.airFriction = function() {
        var _world = _engine.world;
        
        Demo.reset();
        
        World.add(_world, [
            Bodies.rectangle(200, 100, 60, 60, { frictionAir: 0.001 }),
            Bodies.rectangle(400, 100, 60, 60, { frictionAir: 0.05 }),
            Bodies.rectangle(600, 100, 60, 60, { frictionAir: 0.1 })
        ]);

        var renderOptions = _engine.render.options;
        renderOptions.showAngleIndicator = false;
        renderOptions.showVelocity = true;
    };

    Demo.staticFriction = function() {
        var _world = _engine.world;

        Demo.reset();

        var body = Bodies.rectangle(400, 500, 200, 60, { isStatic: true, chamfer: 10 }),
            size = 50,
            counter = -1;

        var stack = Composites.stack(350, 470 - 6 * size, 1, 6, 0, 0, function(x, y, column, row) {
            return Bodies.rectangle(x, y, size * 2, size, {
                slop: 0.5,
                friction: 1,
                frictionStatic: Infinity
            });
        });
        
        World.add(_world, [body, stack]);

        _sceneEvents.push(
            Events.on(_engine, 'beforeUpdate', function(event) {
                counter += 0.014;

                if (counter < 0) {
                    return;
                }

                var px = 400 + 100 * Math.sin(counter);

                // body is static so must manually update velocity for friction to work
                Body.setVelocity(body, { x: px - body.position.x, y: 0 });
                Body.setPosition(body, { x: px, y: body.position.y });
            })
        );

        var renderOptions = _engine.render.options;
        renderOptions.showAngleIndicator = false;
        renderOptions.showVelocity = true;
    };

    Demo.sleeping = function() {
        var _world = _engine.world;
        
        Demo.reset();
        
        var stack = Composites.stack(50, 50, 12, 3, 0, 0, function(x, y, column, row) {
            switch (Math.round(Common.random(0, 1))) {

            case 0:
                if (Common.random() < 0.8) {
                    return Bodies.rectangle(x, y, Common.random(20, 50), Common.random(20, 50));
                } else {
                    return Bodies.rectangle(x, y, Common.random(80, 120), Common.random(20, 30));
                }
                break;
            case 1:
                return Bodies.polygon(x, y, Math.round(Common.random(1, 8)), Common.random(20, 50));

            }
        });
        
        World.add(_world, stack);

        for (var i = 0; i < stack.bodies.length; i++) {
            Events.on(stack.bodies[i], 'sleepStart sleepEnd', function(event) {
                var body = this;
                console.log('body id', body.id, 'sleeping:', body.isSleeping);
            });
        }

        _engine.enableSleeping = true;
    };

    Demo.broadphase = function() {
        var _world = _engine.world;
        
        Demo.reset();
        
        var stack = Composites.stack(20, 20, 20, 5, 0, 0, function(x, y, column, row) {
            switch (Math.round(Common.random(0, 1))) {

            case 0:
                if (Common.random() < 0.8) {
                    return Bodies.rectangle(x, y, Common.random(20, 50), Common.random(20, 50));
                } else {
                    return Bodies.rectangle(x, y, Common.random(80, 120), Common.random(20, 30));
                }
                break;
            case 1:
                return Bodies.polygon(x, y, Math.round(Common.random(1, 8)), Common.random(20, 50));

            }
        });
        
        World.add(_world, stack);
        
        var renderOptions = _engine.render.options;
        renderOptions.showBroadphase = true;
    };

    Demo.gravity = function() {
        var _world = _engine.world;
        
        Demo.reset();

        _engine.world.gravity.y = -1;
        
        var stack = Composites.stack(20, 20, 20, 5, 0, 0, function(x, y, column, row) {
            switch (Math.round(Common.random(0, 1))) {

            case 0:
                if (Common.random() < 0.8) {
                    return Bodies.rectangle(x, y, Common.random(20, 50), Common.random(20, 50));
                } else {
                    return Bodies.rectangle(x, y, Common.random(80, 120), Common.random(20, 30));
                }
                break;
            case 1:
                return Bodies.polygon(x, y, Math.round(Common.random(1, 8)), Common.random(20, 50));

            }
        });
        
        World.add(_world, stack);
    };
    
    Demo.avalanche = function() {
        var _world = _engine.world;
        
        Demo.reset();
        
        var stack = Composites.stack(20, 20, 20, 5, 0, 0, function(x, y, column, row) {
            return Bodies.circle(x, y, Common.random(10, 20), { friction: 0.00001, restitution: 0.5, density: 0.001 });
        });
        
        World.add(_world, stack);
        
        World.add(_world, [
            Bodies.rectangle(200, 150, 700, 20, { isStatic: true, angle: Math.PI * 0.06 }),
            Bodies.rectangle(500, 350, 700, 20, { isStatic: true, angle: -Math.PI * 0.06 }),
            Bodies.rectangle(340, 580, 700, 20, { isStatic: true, angle: Math.PI * 0.04 })
        ]);
    };
    
    Demo.newtonsCradle = function() {
        var _world = _engine.world;
        
        Demo.reset();
        
        var cradle = Composites.newtonsCradle(280, 100, 5, 30, 200);
        World.add(_world, cradle);
        Body.translate(cradle.bodies[0], { x: -180, y: -100 });
        
        cradle = Composites.newtonsCradle(280, 380, 7, 20, 140);
        World.add(_world, cradle);
        Body.translate(cradle.bodies[0], { x: -140, y: -100 });
        
        var renderOptions = _engine.render.options;
        renderOptions.showVelocity = true;
    };

    Demo.timescale = function() {
        var _world = _engine.world;
        
        Demo.reset();

        var explosion = function(engine) {
            var bodies = Composite.allBodies(engine.world);

            for (var i = 0; i < bodies.length; i++) {
                var body = bodies[i];

                if (!body.isStatic && body.position.y >= 500) {
                    var forceMagnitude = 0.04 * body.mass;

                    Body.applyForce(body, { x: 0, y: 0 }, { 
                        x: (forceMagnitude + Common.random() * forceMagnitude) * Common.choose([1, -1]), 
                        y: -forceMagnitude + Common.random() * -forceMagnitude
                    });
                }
            }
        };

        var timeScaleTarget = 1,
            counter = 0;

        _sceneEvents.push(
            Events.on(_engine, 'afterUpdate', function(event) {
                // tween the timescale for bullet time slow-mo
                _engine.timing.timeScale += (timeScaleTarget - _engine.timing.timeScale) * 0.05;

                counter += 1;

                // every 1.5 sec
                if (counter >= 60 * 1.5) {

                    // flip the timescale
                    if (timeScaleTarget < 1) {
                        timeScaleTarget = 1;
                    } else {
                        timeScaleTarget = 0.05;
                    }

                    // create some random forces
                    explosion(_engine);

                    // reset counter
                    counter = 0;
                }
            })
        );

        var bodyOptions = {
            frictionAir: 0, 
            friction: 0.0001,
            restitution: 0.8
        };
        
        // add some small bouncy circles... remember Swordfish?
        World.add(_world, Composites.stack(20, 100, 15, 3, 20, 40, function(x, y, column, row) {
            return Bodies.circle(x, y, Common.random(10, 20), bodyOptions);
        }));

        // add some larger random bouncy objects
        World.add(_world, Composites.stack(50, 50, 8, 3, 0, 0, function(x, y, column, row) {
            switch (Math.round(Common.random(0, 1))) {

            case 0:
                if (Common.random() < 0.8) {
                    return Bodies.rectangle(x, y, Common.random(20, 50), Common.random(20, 50), bodyOptions);
                } else {
                    return Bodies.rectangle(x, y, Common.random(80, 120), Common.random(20, 30), bodyOptions);
                }
                break;
            case 1:
                return Bodies.polygon(x, y, Math.round(Common.random(4, 8)), Common.random(20, 50), bodyOptions);

            }
        }));
    };
    
    Demo.stack = function() {
        var _world = _engine.world;
        
        Demo.reset();
        
        var stack = Composites.stack(100, 300, 10, 5, 0, 0, function(x, y, column, row) {
            return Bodies.rectangle(x, y, 40, 40);
        });
        
        World.add(_world, stack);
    };
    
    Demo.circleStack = function() {
        var _world = _engine.world;
        
        Demo.reset();
        
        var stack = Composites.stack(100, 100, 10, 10, 20, 0, function(x, y, column, row) {
            return Bodies.circle(x, y, 20);
        });
        
        World.add(_world, stack);
    };
    
    Demo.wreckingBall = function() {
        var _world = _engine.world;
        
        Demo.reset();
        
        var rows = 10,
            yy = 600 - 21 - 40 * rows;
        
        var stack = Composites.stack(400, yy, 5, rows, 0, 0, function(x, y, column, row) {
            return Bodies.rectangle(x, y, 40, 40);
        });
        
        World.add(_world, stack);
        
        var ball = Bodies.circle(100, 400, 50, { density: 0.04, frictionAir: 0.005});
        
        World.add(_world, ball);
        World.add(_world, Constraint.create({
            pointA: { x: 300, y: 100 },
            bodyB: ball
        }));
        
        if (!_isMobile) {
            var renderOptions = _engine.render.options;
            renderOptions.showCollisions = true;
            renderOptions.showVelocity = true;
        }
    };
    
    Demo.ballPool = function() {
        var _world = _engine.world;
        
        Demo.reset();
        
        var stack = Composites.stack(100, 50, 10, 15, 10, 10, function(x, y, column, row) {
            return Bodies.circle(x, y, Common.random(15, 30), { restitution: 0.6, friction: 0.1 });
        });
        
        World.add(_world, [
            stack,
            Bodies.polygon(200, 560, 3, 60),
            Bodies.polygon(400, 560, 5, 60),
            Bodies.rectangle(600, 560, 80, 80)
        ]);
    };
    
    Demo.stress = function() {
        var _world = _engine.world;
        
        Demo.reset();
        
        var stack = Composites.stack(90, 50, 18, 15, 0, 0, function(x, y, column, row) {
            return Bodies.rectangle(x, y, 35, 35);
        });
        
        World.add(_world, stack);

        var renderOptions = _engine.render.options;
        renderOptions.showAngleIndicator = false;
    };
    
    Demo.stress2 = function() {
        var _world = _engine.world;
        
        Demo.reset();
        
        var stack = Composites.stack(100, 120, 25, 18, 0, 0, function(x, y, column, row) {
            return Bodies.rectangle(x, y, 25, 25);
        });
        
        World.add(_world, stack);
        
        var renderOptions = _engine.render.options;
        renderOptions.showAngleIndicator = false;
    };
    
    Demo.pyramid = function() {
        var _world = _engine.world;
        
        Demo.reset();
        
        var stack = Composites.pyramid(100, 258, 15, 10, 0, 0, function(x, y, column, row) {
            return Bodies.rectangle(x, y, 40, 40);
        });
        
        World.add(_world, stack);
    };
    
    Demo.restitution = function() {
        var _world = _engine.world;
        
        Demo.reset();
        
        var rest = 0.9, 
            space = 600 / 5;
    
        World.add(_world, [
            Bodies.rectangle(100 + space * 0, 150, 50, 50, { restitution: rest }),
            Bodies.rectangle(100 + space * 1, 150, 50, 50, { restitution: rest, angle: -Math.PI * 0.15 }),
            Bodies.rectangle(100 + space * 2, 150, 50, 50, { restitution: rest, angle: -Math.PI * 0.25 }),
            Bodies.circle(100 + space * 3, 150, 25, { restitution: rest }),
            Bodies.rectangle(100 + space * 5, 150, 180, 20, { restitution: rest, angle: -Math.PI * 0.5 })
        ]);
        
        var renderOptions = _engine.render.options;
        renderOptions.showCollisions = true;
        renderOptions.showVelocity = true;
        renderOptions.showAngleIndicator = true;
    };

    Demo.softBody = function() {
        var _world = _engine.world;
        
        Demo.reset();

        var particleOptions = { 
            friction: 0.05,
            frictionStatic: 0.1,
            render: { visible: true } 
        };

        World.add(_world, [
            Composites.softBody(250, 100, 5, 5, 0, 0, true, 18, particleOptions),
            Composites.softBody(250, 300, 8, 3, 0, 0, true, 15, particleOptions),
            Composites.softBody(250, 400, 4, 4, 0, 0, true, 15, particleOptions)
        ]);

        var renderOptions = _engine.render.options;
        renderOptions.showAngleIndicator = false;
    };

    Demo.cloth = function() {
        var _world = _engine.world;
        
        Demo.reset();

        var group = Body.nextGroup(true),
            particleOptions = { friction: 0.00001, collisionFilter: { group: group }, render: { visible: false }},
            cloth = Composites.softBody(200, 200, 20, 12, 5, 5, false, 8, particleOptions);

        for (var i = 0; i < 20; i++) {
            cloth.bodies[i].isStatic = true;
        }

        World.add(_world, [
            cloth,
            Bodies.circle(300, 500, 80, { isStatic: true }),
            Bodies.rectangle(500, 480, 80, 80, { isStatic: true })
        ]);
    };

    Demo.catapult = function() {
        var _world = _engine.world;
        
        Demo.reset();

        var stack = Composites.stack(250, 255, 1, 6, 0, 0, function(x, y, column, row) {
            return Bodies.rectangle(x, y, 30, 30);
        });

        var catapult = Bodies.rectangle(400, 520, 320, 20, {  });

        World.add(_world, [
            stack,
            catapult,
            Bodies.rectangle(250, 555, 20, 50, { isStatic: true }),
            Bodies.circle(560, 100, 50, { density: 0.005 }),
            Constraint.create({ bodyA: catapult, pointB: { x: 390, y: 580 } }),
            Constraint.create({ bodyA: catapult, pointB: { x: 410, y: 580 } })
        ]);
        
        var renderOptions = _engine.render.options;
        renderOptions.showCollisions = true;
        renderOptions.showVelocity = true;
        renderOptions.showAngleIndicator = true;
    };

    Demo.beachBalls = function() {
        var _world = _engine.world;
        
        Demo.reset();
        
        var stack = Composites.stack(0, 100, 5, 1, 20, 0, function(x, y, column, row) {
            return Bodies.circle(x, y, 75, { restitution: 0.9 });
        });
        
        World.add(_world, stack);
    };

    Demo.events = function() {
        var _world = _engine.world;
        
        Demo.reset();

        // bind events (_sceneEvents is only used for this demo)

        _sceneEvents.push(

            // an example of using composite events on the world
            Events.on(_world, 'afterAdd', function(event) {
                console.log('added to world:', event.object);
            })

        );

        _sceneEvents.push(

            // an example of using beforeUpdate event on an engine
            Events.on(_engine, 'beforeUpdate', function(event) {
                var engine = event.source;

                // apply random forces every 5 secs
                if (event.timestamp % 5000 < 50)
                    shakeScene(engine);
            })

        );

        _sceneEvents.push(

            // an example of using collisionStart event on an engine
            Events.on(_engine, 'collisionStart', function(event) {
                var pairs = event.pairs;

                // change object colours to show those starting a collision
                for (var i = 0; i < pairs.length; i++) {
                    var pair = pairs[i];
                    pair.bodyA.render.fillStyle = '#bbbbbb';
                    pair.bodyB.render.fillStyle = '#bbbbbb';
                }
            })

        );

        _sceneEvents.push(

            // an example of using collisionActive event on an engine
            Events.on(_engine, 'collisionActive', function(event) {
                var pairs = event.pairs;

                // change object colours to show those in an active collision (e.g. resting contact)
                for (var i = 0; i < pairs.length; i++) {
                    var pair = pairs[i];
                    pair.bodyA.render.fillStyle = '#aaaaaa';
                    pair.bodyB.render.fillStyle = '#aaaaaa';
                }
            })

        );

        _sceneEvents.push(

            // an example of using collisionEnd event on an engine
            Events.on(_engine, 'collisionEnd', function(event) {
                var pairs = event.pairs;

                // change object colours to show those ending a collision
                for (var i = 0; i < pairs.length; i++) {
                    var pair = pairs[i];
                    pair.bodyA.render.fillStyle = '#999999';
                    pair.bodyB.render.fillStyle = '#999999';
                }
            })

        );

        _sceneEvents.push(

            // an example of using mouse events on a mouse
            Events.on(_mouseConstraint, 'mousedown', function(event) {
                var mousePosition = event.mouse.position;
                console.log('mousedown at ' + mousePosition.x + ' ' + mousePosition.y);
                _engine.render.options.background = 'cornsilk';
                shakeScene(_engine);
            })

        );

        _sceneEvents.push(

            // an example of using mouse events on a mouse
            Events.on(_mouseConstraint, 'mouseup', function(event) {
                var mousePosition = event.mouse.position;
                _engine.render.options.background = "white";
                console.log('mouseup at ' + mousePosition.x + ' ' + mousePosition.y);
            })

        );

        _sceneEvents.push(

            // an example of using mouse events on a mouse
            Events.on(_mouseConstraint, 'startdrag', function(event) {
                console.log('startdrag', event);
            })

        );

        _sceneEvents.push(

            // an example of using mouse events on a mouse
            Events.on(_mouseConstraint, 'enddrag', function(event) {
                console.log('enddrag', event);
            })

        );

        // scene code

        var stack = Composites.stack(50, 100, 8, 4, 50, 50, function(x, y, column, row) {
            return Bodies.circle(x, y, 15, { restitution: 1, render: { strokeStyle: '#777' } });
        });
        
        World.add(_world, stack);

        var renderOptions = _engine.render.options;
        renderOptions.wireframes = false;

        var shakeScene = function(engine) {
            var bodies = Composite.allBodies(engine.world);

            for (var i = 0; i < bodies.length; i++) {
                var body = bodies[i];

                if (!body.isStatic && body.position.y >= 500) {
                    var forceMagnitude = 0.01 * body.mass;

                    Body.applyForce(body, { x: 0, y: 0 }, { 
                        x: (forceMagnitude + Common.random() * forceMagnitude) * Common.choose([1, -1]), 
                        y: -forceMagnitude + Common.random() * -forceMagnitude
                    });
                }
            }
        };
    };

    Demo.sprites = function() {
        var _world = _engine.world,
            offset = 10,
            options = { 
                isStatic: true,
                render: {
                    visible: false
                }
            };

        Demo.reset();
        _world.bodies = [];

        // these static walls will not be rendered in this sprites example, see options
        World.add(_world, [
            Bodies.rectangle(400, -offset, 800.5 + 2 * offset, 50.5, options),
            Bodies.rectangle(400, 600 + offset, 800.5 + 2 * offset, 50.5, options),
            Bodies.rectangle(800 + offset, 300, 50.5, 600.5 + 2 * offset, options),
            Bodies.rectangle(-offset, 300, 50.5, 600.5 + 2 * offset, options)
        ]);

        var stack = Composites.stack(20, 20, 10, 4, 0, 0, function(x, y, column, row) {
            if (Common.random() > 0.35) {
                return Bodies.rectangle(x, y, 64, 64, {
                    render: {
                        strokeStyle: '#ffffff',
                        sprite: {
                            texture: './img/box.png'
                        }
                    }
                });
            } else {
                return Bodies.circle(x, y, 46, {
                    density: 0.0005,
                    frictionAir: 0.06,
                    restitution: 0.3,
                    friction: 0.01,
                    render: {
                        sprite: {
                            texture: './img/ball.png'
                        }
                    }
                });
            }
        });

        World.add(_world, stack);

        var renderOptions = _engine.render.options;
        renderOptions.background = './img/wall-bg.jpg';
        renderOptions.showAngleIndicator = false;
        renderOptions.wireframes = false;
    };

    Demo.raycasting = function() {
        var _world = _engine.world;
        
        Demo.reset();
        
        var stack = Composites.stack(20, 20, 15, 4, 0, 0, function(x, y, column, row) {
            switch (Math.round(Common.random(0, 1))) {

            case 0:
                if (Common.random() < 0.8) {
                    return Bodies.rectangle(x, y, Common.random(20, 50), Common.random(20, 50));
                } else {
                    return Bodies.rectangle(x, y, Common.random(80, 120), Common.random(20, 30));
                }
                break;
            case 1:
                var sides = Math.round(Common.random(1, 8));
                sides = (sides === 3) ? 4 : sides;
                return Bodies.polygon(x, y, sides, Common.random(20, 50));
            }
        });

        var star = Vertices.fromPath('50 0 63 38 100 38 69 59 82 100 50 75 18 100 31 59 0 38 37 38'),
            concave = Bodies.fromVertices(200, 200, star);
        
        World.add(_world, [stack, concave]);

        _sceneEvents.push(
            Events.on(_engine.render, 'afterRender', function() {
                var mouse = _mouseConstraint.mouse,
                    context = _engine.render.context,
                    bodies = Composite.allBodies(_engine.world),
                    startPoint = { x: 400, y: 100 },
                    endPoint = mouse.position;

                var collisions = Query.ray(bodies, startPoint, endPoint);

                context.beginPath();
                context.moveTo(startPoint.x, startPoint.y);
                context.lineTo(endPoint.x, endPoint.y);
                if (collisions.length > 0) {
                    context.strokeStyle = '#fff';
                } else {
                    context.strokeStyle = '#555';
                }
                context.lineWidth = 0.5;
                context.stroke();

                for (var i = 0; i < collisions.length; i++) {
                    var collision = collisions[i];
                    context.rect(collision.bodyA.position.x - 4.5, collision.bodyA.position.y - 4.5, 8, 8);
                }

                context.fillStyle = 'rgba(255,165,0,0.7)';
                context.fill();
            })
        );
    };

    Demo.collisionFiltering = function() {
        var _world = _engine.world;

        // define our categories (as bit fields, there are up to 32 available)
        var defaultCategory = 0x0001,
            redCategory = 0x0002,
            greenCategory = 0x0004,
            blueCategory = 0x0008;

        var redColor = '#C44D58',
            blueColor = '#4ECDC4',
            greenColor = '#C7F464';

        Demo.reset();

        // create a stack with varying body categories (but these bodies can all collide with each other)
        World.add(_world,
            Composites.stack(275, 150, 5, 10, 10, 10, function(x, y, column, row) {
                var category = redCategory,
                    color = redColor;

                if (row > 5) {
                    category = blueCategory;
                    color = blueColor;
                } else if (row > 2) {
                    category = greenCategory;
                    color = greenColor;
                }

                return Bodies.circle(x, y, 20, {
                    collisionFilter: {
                        category: category
                    },
                    render: {
                        strokeStyle: color,
                        fillStyle: 'transparent'
                    }
                });
            })
        );

        // this body will only collide with the walls and the green bodies
        World.add(_world,
            Bodies.circle(310, 40, 30, {
                collisionFilter: {
                    mask: defaultCategory | greenCategory
                },
                render: {
                    strokeStyle: Common.shadeColor(greenColor, -20),
                    fillStyle: greenColor
                }
            })
        );

        // this body will only collide with the walls and the red bodies
        World.add(_world,
            Bodies.circle(400, 40, 30, {
                collisionFilter: {
                    mask: defaultCategory | redCategory
                },
                render: {
                    strokeStyle: Common.shadeColor(redColor, -20),
                    fillStyle: redColor
                }
            })
        );

        // this body will only collide with the walls and the blue bodies
        World.add(_world,
            Bodies.circle(480, 40, 30, {
                collisionFilter: {
                    mask: defaultCategory | blueCategory
                },
                render: {
                    strokeStyle: Common.shadeColor(blueColor, -20),
                    fillStyle: blueColor
                }
            })
        );

        // red category objects should not be draggable with the mouse
        _mouseConstraint.collisionFilter.mask = defaultCategory | blueCategory | greenCategory;

        var renderOptions = _engine.render.options;
        renderOptions.wireframes = false;
        renderOptions.background = '#222';
        renderOptions.showAngleIndicator = false;
    };

    // the functions for the demo interface and controls below

    Demo.initControls = function() {
        var demoSelect = document.getElementById('demo-select'),
            demoReset = document.getElementById('demo-reset');

        // create a Matter.Gui
        if (!_isMobile && Gui) {
            _gui = Gui.create(_engine, _runner);

            // need to add mouse constraint back in after gui clear or load is pressed
            Events.on(_gui, 'clear load', function() {
                _mouseConstraint = MouseConstraint.create(_engine);
                World.add(_engine.world, _mouseConstraint);
            });

            // need to rebind mouse on render change
            Events.on(_gui, 'setRenderer', function() {
                Mouse.setElement(_mouseConstraint.mouse, _engine.render.canvas);
            });
        }

        // create a Matter.Inspector
        if (!_isMobile && Inspector && _useInspector) {
            _inspector = Inspector.create(_engine, _runner);

            Events.on(_inspector, 'import', function() {
                _mouseConstraint = MouseConstraint.create(_engine);
                World.add(_engine.world, _mouseConstraint);
            });

            Events.on(_inspector, 'play', function() {
                _mouseConstraint = MouseConstraint.create(_engine);
                World.add(_engine.world, _mouseConstraint);
            });

            Events.on(_inspector, 'selectStart', function() {
                _mouseConstraint.constraint.render.visible = false;
            });

            Events.on(_inspector, 'selectEnd', function() {
                _mouseConstraint.constraint.render.visible = true;
            });
        }

        // go fullscreen when using a mobile device
        if (_isMobile) {
            var body = document.body;

            body.className += ' is-mobile';
            _engine.render.canvas.addEventListener('touchstart', Demo.fullscreen);

            var fullscreenChange = function() {
                var fullscreenEnabled = document.fullscreenEnabled || document.mozFullScreenEnabled || document.webkitFullscreenEnabled;

                // delay fullscreen styles until fullscreen has finished changing
                setTimeout(function() {
                    if (fullscreenEnabled) {
                        body.className += ' is-fullscreen';
                    } else {
                        body.className = body.className.replace('is-fullscreen', '');
                    }
                }, 2000);
            };

            document.addEventListener('webkitfullscreenchange', fullscreenChange);
            document.addEventListener('mozfullscreenchange', fullscreenChange);
            document.addEventListener('fullscreenchange', fullscreenChange);
        }

        // initialise demo selector
        demoSelect.value = _sceneName;
        
        demoSelect.addEventListener('change', function(e) {
            Demo[_sceneName = e.target.value]();
            Gui.update(_gui);
            
            var scrollY = window.scrollY;
            window.location.hash = _sceneName;
            window.scrollY = scrollY;
        });
        
        demoReset.addEventListener('click', function(e) {
            Demo[_sceneName]();
            Gui.update(_gui);
        });
    };

    Demo.fullscreen = function(){
        var _fullscreenElement = _engine.render.canvas;
        
        if (!document.fullscreenElement && !document.mozFullScreenElement && !document.webkitFullscreenElement) {
            if (_fullscreenElement.requestFullscreen) {
                _fullscreenElement.requestFullscreen();
            } else if (_fullscreenElement.mozRequestFullScreen) {
                _fullscreenElement.mozRequestFullScreen();
            } else if (_fullscreenElement.webkitRequestFullscreen) {
                _fullscreenElement.webkitRequestFullscreen(Element.ALLOW_KEYBOARD_INPUT);
            }
        }
    };
    
    Demo.reset = function() {
        var _world = _engine.world;
        
        World.clear(_world);
        Engine.clear(_engine);

        // clear scene graph (if defined in controller)
        if (_engine.render) {
            var renderController = _engine.render.controller;
            if (renderController && renderController.clear)
                renderController.clear(_engine.render);
        }

        // clear all scene events
        for (var i = 0; i < _sceneEvents.length; i++)
            Events.off(_engine, _sceneEvents[i]);

        if (_mouseConstraint && _mouseConstraint.events) {
            for (i = 0; i < _sceneEvents.length; i++)
                Events.off(_mouseConstraint, _sceneEvents[i]);
        }

        if (_world.events) {
            for (i = 0; i < _sceneEvents.length; i++)
                Events.off(_world, _sceneEvents[i]);
        }

        if (_runner && _runner.events) {
            for (i = 0; i < _sceneEvents.length; i++)
                Events.off(_runner, _sceneEvents[i]);
        }

        if (_engine.render && _engine.render.events) {
            for (i = 0; i < _sceneEvents.length; i++)
                Events.off(_engine.render, _sceneEvents[i]);
        }

        _sceneEvents = [];

        // reset id pool
        Common._nextId = 0;

        // reset random seed
        Common._seed = 0;

        // reset mouse offset and scale (only required for Demo.views)
        if (_mouseConstraint) {
            Mouse.setScale(_mouseConstraint.mouse, { x: 1, y: 1 });
            Mouse.setOffset(_mouseConstraint.mouse, { x: 0, y: 0 });
        }

        _engine.enableSleeping = false;
        _engine.world.gravity.y = 1;
        _engine.world.gravity.x = 0;
        _engine.timing.timeScale = 1;

        var offset = 5;
        World.add(_world, [
            Bodies.rectangle(400, -offset, 800.5 + 2 * offset, 50.5, { isStatic: true }),
            Bodies.rectangle(400, 600 + offset, 800.5 + 2 * offset, 50.5, { isStatic: true }),
            Bodies.rectangle(800 + offset, 300, 50.5, 600.5 + 2 * offset, { isStatic: true }),
            Bodies.rectangle(-offset, 300, 50.5, 600.5 + 2 * offset, { isStatic: true })
        ]);

        if (_mouseConstraint) {
            World.add(_world, _mouseConstraint);
        }
        
        if (_engine.render) {
            var renderOptions = _engine.render.options;
            renderOptions.wireframes = true;
            renderOptions.hasBounds = false;
            renderOptions.showDebug = false;
            renderOptions.showBroadphase = false;
            renderOptions.showBounds = false;
            renderOptions.showVelocity = false;
            renderOptions.showCollisions = false;
            renderOptions.showAxes = false;
            renderOptions.showPositions = false;
            renderOptions.showAngleIndicator = true;
            renderOptions.showIds = false;
            renderOptions.showShadows = false;
            renderOptions.showVertexNumbers = false;
            renderOptions.showConvexHulls = false;
            renderOptions.showInternalEdges = false;
            renderOptions.showSeparations = false;
            renderOptions.background = '#fff';
        }

        if (_isMobile)
            renderOptions.showDebug = true;
    };

})();