Just playing around with animating HTML5 Canvas elements with Javascript. I started with this basic horizontally moving rectangle, then added some trig code to move multiple objects around in a circle. Here’s a demo.
If the Math.sin() & Math.cos() is confusing, watch the video tutorials on Trig and Unit Circle in particular at the Khan Academy.
<!DOCTYPE HTML>
<html>
<head>
<style>
body {
margin: 0px;
padding: 0px;
}
#myCanvas {
border: 1px solid #9C9898;
}
</style>
<script>
var numsqr = 40;
var mShapes = [];
window.requestAnimFrame = (function(callback){
return window.requestAnimationFrame ||
window.webkitRequestAnimationFrame ||
window.mozRequestAnimationFrame ||
window.oRequestAnimationFrame ||
window.msRequestAnimationFrame ||
function(callback){
window.setTimeout(callback, 1000 / 60);
};
})();
function drawRect(myRectangle){
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");
context.beginPath();
context.rect(myRectangle.x, myRectangle.y, myRectangle.width, myRectangle.height);
context.fillStyle = "#8ED6FF";
context.fill();
context.lineWidth = myRectangle.borderWidth;
context.strokeStyle = "black";
context.stroke();
}
function animate(lastTime, mShapes, animProp){
if (animProp.animate) {
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");
// update
var date = new Date();
var time = date.getTime();
var timeDiff = time - lastTime;
for(var j = 0; j < numsqr; j++){
//circles around a midpoint in a larger circle, specified by the radius
mShapes[j].x = mShapes[j].centerX + Math.cos( mShapes[j].angle * Math.PI/180 ) * mShapes[j].radius;
mShapes[j].y = mShapes[j].centerY + Math.sin( mShapes[j].angle * Math.PI/180 ) * mShapes[j].radius;
(mShapes[j].angle < 360) ? mShapes[j].angle += 1 : mShapes[j].angle = 0;
}
lastTime = time;
// clear
context.clearRect(0, 0, canvas.width, canvas.height);
// draw
for(var l = 0; l < numsqr; l++)
drawRect(mShapes[l]);
// request new frame
requestAnimFrame(function(){
animate(lastTime, mShapes, animProp);
});
}
}
window.onload = function(){
for(var i = 0; i < numsqr; i++){
mShapes[i] = {
angle:0,
width:20,
height:20,
x: 100 + i*10,
y: 250,
centerX: 290,
centerY: 290,
radius: 250 - (1 + i * 5),
borderWidth: 1
};
}
/*
* make the animation properties an object
* so that it can be modified by reference
* from an event
*/
var animProp = {
animate: false
};
// add click listener to canvas
document.getElementById("myCanvas").addEventListener("click", function(){
if (animProp.animate) {
animProp.animate = false;
}
else {
animProp.animate = true;
var date = new Date();
var time = date.getTime();
animate(time, mShapes, animProp);
}
});
for(var k = 0; k < numsqr; k++)
drawRect( mShapes[k] );
};
</script>
</head>
<body onmousedown="return false;">
<canvas id="myCanvas" width="600" height="600"></canvas>
</body>
</html>
timshaya 