var output;
var canvas;
var context;

var width = 640;
var height = 480;

var gCells;

var stepIntervalID;
var frameRate = 40;
var stepDuration = 1000/frameRate;
var time;

function init () {
    output = document.getElementById("output");
    canvas = document.getElementById("canvas");
    canvas.width = width;
    canvas.height = height;
    context = canvas.getContext("2d");

    time = 0;
}


function main () {
    init();

    stepIntervalID = setInterval("step();", stepDuration);
}

function step () {
    context.fillStyle = "rgba(0,0,255, 0.5)";
    context.beginPath();
    var x = width/2 + Math.sin(time*0.1)*200;
    var y = height/2 + Math.sin(time*0.15+Math.PI/2)*200;
    context.arc(x,y, 10, 0,7);
    context.fill();

    time += 1;
}