(function() {

    var World = Matter.World,
        Bodies = Matter.Bodies,
        Composites = Matter.Composites,
        Common = Matter.Common,
        Vertices = Matter.Vertices;

    Example.concave = function(demo) {
        var engine = demo.engine,
            world = engine.world;

        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) {
            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 = demo.render.options;
        renderOptions.showAngleIndicator = false;
    };

})();