added Example.doublePendulum

demo/index.html

@@ -44,6 +44,7 @@
     <script src="../examples/compound.js"></script>
     <script src="../examples/compoundStack.js"></script>
     <script src="../examples/concave.js"></script>
+    <script src="../examples/doublePendulum.js"></script>
     <script src="../examples/events.js"></script>
     <script src="../examples/friction.js"></script>
     <script src="../examples/gravity.js"></script>

demo/js/Demo.js

@@ -118,6 +118,12 @@
                 init: Example.concave,
                 sourceLink: sourceLinkRoot + '/concave.js'
             },
+            {
+                name: 'Double Pendulum',
+                id: 'doublePendulum',
+                init: Example.doublePendulum,
+                sourceLink: sourceLinkRoot + '/doublePendulum.js'
+            },
             {
                 name: 'Events',
                 id: 'events',

examples/doublePendulum.js

@@ -0,0 +1,151 @@
+var Example = Example || {};
+
+Example.doublePendulum = function() {
+    var Engine = Matter.Engine,
+        Events = Matter.Events,
+        Render = Matter.Render,
+        Runner = Matter.Runner,
+        Body = Matter.Body,
+        Composite = Matter.Composite,
+        Composites = Matter.Composites,
+        Constraint = Matter.Constraint,
+        MouseConstraint = Matter.MouseConstraint,
+        Mouse = Matter.Mouse,
+        World = Matter.World,
+        Bodies = Matter.Bodies,
+        Vector = Matter.Vector;
+
+    // create engine
+    var engine = Engine.create(),
+        world = engine.world;
+
+    // create renderer
+    var render = Render.create({
+        element: document.body,
+        engine: engine,
+        options: {
+            width: Math.min(document.documentElement.clientWidth, 800),
+            height: Math.min(document.documentElement.clientHeight, 600),
+            wireframes: false,
+            background: '#0f0f13'
+        }
+    });
+
+    Render.run(render);
+
+    // create runner
+    var runner = Runner.create();
+    Runner.run(runner, engine);
+
+    // add bodies
+    var group = Body.nextGroup(true),
+        length = 200,
+        width = 25;
+        
+    var pendulum = Composites.stack(350, 160, 2, 1, 0, 0, function(x, y) {
+        return Bodies.rectangle(x, y, length, width, { 
+            collisionFilter: { group: group },
+            frictionAir: 0,
+            chamfer: 5,
+            render: {
+                fillStyle: 'transparent',
+                lineWidth: 1
+            }
+        });
+    });
+
+    pendulum.bodies[0].render.strokeStyle = '#4a485b';
+    pendulum.bodies[1].render.strokeStyle = '#4a485b';
+    
+    Composites.chain(pendulum, 0.5, 0, -0.5, 0, { 
+        stiffness: 1, 
+        length: 0,
+        angularStiffness: 0.7,
+        render: {
+            lineWidth: 0
+        }
+    });
+    
+    Composite.add(pendulum, Constraint.create({ 
+        bodyB: pendulum.bodies[0],
+        pointB: { x: -length * 0.5, y: 0 },
+        pointA: { x: pendulum.bodies[0].position.x - length * 0.5, y: pendulum.bodies[0].position.y },
+        stiffness: 1,
+        length: 0,
+        render: {
+            lineWidth: 0
+        }
+    }));
+
+    var lowerArm = pendulum.bodies[1];
+
+    Body.rotate(lowerArm, -Math.PI * 0.3, {
+        x: lowerArm.position.x - 100,
+        y: lowerArm.position.y
+    });
+    
+    World.add(world, pendulum);
+
+    var trail = [];
+
+    Events.on(render, 'afterRender', function() {
+        trail.unshift({
+            position: Vector.clone(lowerArm.position),
+            speed: lowerArm.speed
+        });
+
+        Render.startViewTransform(render);
+        render.context.globalAlpha = 0.7;
+
+        for (var i = 0; i < trail.length; i += 1) {
+            var point = trail[i].position,
+                speed = trail[i].speed;
+            
+            var hue = 250 + Math.round((1 - Math.min(1, speed / 10)) * 170);
+            render.context.fillStyle = 'hsl(' + hue + ', 100%, 55%)';
+            render.context.fillRect(point.x, point.y, 2, 2);
+        }
+
+        render.context.globalAlpha = 1;
+        Render.endViewTransform(render);
+
+        if (trail.length > 2000) {
+            trail.pop();
+        }
+    });
+
+    // add mouse control
+    var mouse = Mouse.create(render.canvas),
+        mouseConstraint = MouseConstraint.create(engine, {
+            mouse: mouse,
+            constraint: {
+                stiffness: 0.2,
+                render: {
+                    visible: false
+                }
+            }
+        });
+
+    World.add(world, mouseConstraint);
+
+    // keep the mouse in sync with rendering
+    render.mouse = mouse;
+
+    // fit the render viewport to the scene
+    Render.lookAt(render, {
+        min: { x: 0, y: 0 },
+        max: { x: 700, y: 600 }
+    });
+
+    // context for MatterTools.Demo
+    return {
+        engine: engine,
+        runner: runner,
+        render: render,
+        canvas: render.canvas,
+        stop: function() {
+            Matter.Render.stop(render);
+            Matter.Runner.stop(runner);
+        }
+    };
+};