Canvas动态创建验证码案例
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Canvas创建验证码</title>
</head>
<body>
<div onclick='getImage()'>
<canvas id='canvas' style="cursor: pointer;"></canvas>
</div>
<script type="text/javascript">
function getImage(){
var cw = 120; //画布的总宽度
var ch = 30; //画布的总高度
canvas.width = cw;
canvas.height = ch;
var ctx = canvas.getContext('2d');
/**1.绘制背景颜色——填充矩形**/
ctx.fillStyle = rc(150, 230);
ctx.fillRect(0, 0, cw, ch);
/**2.循环绘制4个随机字符**/
ctx.textBaseline = 'top';
var pool = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
for (var i = 0; i < 4; i++) {
var c = pool[rn(0, pool.length)];//一个随机字符
this.code+=c;
var fs = rn(10, 40); //字体大小
ctx.font = fs + 'px SimHei';
var fc = rc(50, 150); //字体颜色
ctx.strokeStyle = fc;
var deg = rn(-45, 45);//旋转角度
var x = -fs / 2; //每个字符左上角的坐标
var y = -fs / 2;
//绘制一个字符: 保存状态->平移->旋转->绘制->恢复状态
ctx.save();
ctx.translate(30*i+15, 15);
ctx.rotate(deg*Math.PI/180);
ctx.strokeText(c, x, y);
ctx.restore();
}
/**3.绘制5条干扰线——直线路径**/
for(var i=0; i<5; i++){
ctx.beginPath();
ctx.moveTo(rn(0,cw), rn(0, ch));
ctx.lineTo(rn(0,cw), rn(0, ch));
ctx.strokeStyle = rc(0, 255);
ctx.stroke();
}
/**4.绘制50个杂色点——半径为0.5圆形路径**/
for(var i=0; i<50; i++){
ctx.beginPath();
ctx.arc(rn(0,cw), rn(0, ch),0.5, 0, 2*Math.PI);
ctx.fillStyle = rc(0, 255);
ctx.fill();
}
//random number，返回指定范围内的随机整数
function rn(min, max) {
return Math.floor(Math.random() * (max - min) + min);
}
//random color，返回指定范围内的随机颜色
function rc(min, max) {
var r = rn(min, max);
var g = rn(min, max);
var b = rn(min, max);
return "rgb("+r+","+g+","+b+")";
}
}
getImage()
</script>
</body>
</html>
