HTML5 Canvas animation effect demonstration
Main idea:
First, prepare a picture with consecutive frames, and then use the draw method of HTML5 Canvas to draw different frames at different time
intervals, so that it looks like the animation is playing.
Key technical points:
The JavaScript function setTimeout() has two parameters. The first one is that the parameter can Pass a JavaScript method,
The other parameter represents the interval, in milliseconds. Code example:
setTimeout(update, 1000/30);
Canvas API-drawImage() method, all 9 need to be specified Parameters:
ctx.drawImage(myImage, offw, offh, width,height, x2, y2, width, height);
where offw, offh refer to the starting coordinate point of the source image, width, height represent the width and height of the source image, x2, y2 represent the starting point of the source image on the target Canvas Coordinate points.
The effect achieved by a 22-frame wild goose flying picture:
## Source image: 
Program code:
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="X-UA-Compatible" content="chrome=IE8">
<meta http-equiv="Content-type" content="text/html;charset=UTF-8">
<title>Canvas Mouse Event Demo</title>
<link href="default.css" rel="stylesheet" />
<script>
var ctx = null; // global variable 2d context
var started = false;
var mText_canvas = null;
var x = 0, y =0;
var frame = 0; // 22 5*5 + 2
var imageReady = false;
var myImage = null;
var px = 300;
var py = 300;
var x2 = 300;
var y2 = 0;
window.onload = function() {
var canvas = document.getElementById("animation_canvas");
console.log(canvas.parentNode.clientWidth);
canvas.width = canvas.parentNode.clientWidth;
canvas.height = canvas.parentNode.clientHeight;
if (!canvas.getContext) {
console.log("Canvas not supported. Please install a HTML5 compatible browser.");
return;
}
// get 2D context of canvas and draw rectangel
ctx = canvas.getContext("2d");
ctx.fillStyle="black";
ctx.fillRect(0, 0, canvas.width, canvas.height);
myImage = document.createElement('img');
myImage.src = "../robin.png";
myImage.onload = loaded();
}
function loaded() {
imageReady = true;
setTimeout( update, 1000/30);
}
function redraw() {
ctx.clearRect(0, 0, 460, 460)
ctx.fillStyle="black";
ctx.fillRect(0, 0, 460, 460);
// find the index of frames in image
var height = myImage.naturalHeight/5;
var width = myImage.naturalWidth/5;
var row = Math.floor(frame / 5);
var col = frame - row * 5;
var offw = col * width;
var offh = row * height;
// first robin
px = px - 5;
py = py - 5;
if(px < -50) {
px = 300;
}
if(py < -50) {
py = 300;
}
//var rate = (frame+1) /22;
//var rw = Math.floor(rate * width);
//var rh = Math.floor(rate * height);
ctx.drawImage(myImage, offw, offh, width, height, px, py, width, height);
// second robin
x2 = x2 - 5;
y2 = y2 + 5;
if(x2 < -50) {
x2 = 300;
y2 = 0;
}
ctx.drawImage(myImage, offw, offh, width, height, x2, y2, width, height);
}
function update() {
redraw();
frame++;
if (frame >= 22) frame = 0;
setTimeout( update, 1000/30);
}
</script>
</head>
<body>
<h1>HTML Canvas Animations Demo - By Gloomy Fish</h1>
<pre class="brush:php;toolbar:false">Play Animations