Cannonball

    (function () {
        var board = JXG.JSXGraph.initBoard('cannon', {boundingbox: [0, 10, 20, 0], showCopyright: false, showNavigation: false}),
            bottom = board.create('image', ['img/cannon_bottom.png', [0, 0.3], [2, 1]], {layer: 1}),
            muzzle = board.create('image', ['img/cannon_muzzle.png', [0, 1.05], [3, 0.75]], {layer: 0}),
            shoot = board.create('text', [9, 9.5, '<button id="shoot">Shoot</button>']),
            reset = board.create('text', [11, 9.5, '<button id="reset">Reset</button>']),
            rot, rp, cp, cc, cannonball, cbanim, solution, velocity,

            animTime = function () {
                return 3000;
            },

            fAngle = function () {
                return Math.atan2(cp.Y()-rp.Y(),cp.X()-rp.X());
            },

            fSolution = function (x) {
                var b = fAngle(),
                    g = 9.81/2;

                return Math.tan(b)*(x - cannonball.X()) - g*(Math.pow((x - cannonball.X())/(velocity.Value()*Math.cos(b)), 2)) + cannonball.Y();
            },

            fAnim = function (t) {
                var i = Math.floor(solution.points.length*t/animTime())/*3 + 17*t/animTime()*/,
                    s = NaN;

                if (JXG.exists(solution.points[i]) && solution.points[i].usrCoords[2] > 0) {
                    s = solution.points[i].usrCoords.slice(1);
                }

                return s;
            };

        board.options.animationDelay = 50;

        velocity = board.create('slider', [[1, 9.5], [6, 9.5], [0, 5, 15]], {name: 'Velocity'});

        cp = board.create('point', [1.4, 1.4], {fixed: true, visible: false});
        cc = board.create('circle', [cp, 1.25], {visible: false});
        rp = board.create('glider', [0, 1.4, cc], {withLabel: false, showInfobox: false, color: 'black'});

        rot = board.create('transform', [fAngle, cp], {type: 'rotate'});
        rot.bindTo(muzzle);

        cannonball = board.create('point', [3, 1.4], {size: 8, strokeColor: 'black', fillColor: 'gray', withLabel: false, fixed: true});
        cbanim = board.create('point', [3, 1.4], {size: 8, strokeColor: 'black', fillColor: 'gray', withLabel: false, fixed: true, visible: false});
        rot.bindTo(cannonball);
        solution = board.create('plot', [fSolution, function () { return cannonball.X(); }, 20], {visible: true, doAdvancedPlot: false});


        JXG.addEvent(document.getElementById('shoot'), 'click', function () {
            cannonball.setProperty({
                visible: false
            });
            cbanim.setProperty({
                visible: true
            });
            cbanim.moveTo([cannonball.X(), cannonball.Y()]);

            cbanim.moveAlong(fAnim, animTime(), {
                callback: function () {
                    // this is executed when the animation is finished
                }
            });
        }, this);

        JXG.addEvent(document.getElementById('reset'), 'click', function () {
            board.stopAllAnimation();
            cbanim.setProperty({visible: false});
            cannonball.setProperty({visible: true});
        }, this);

    })();