Html验证码

var show_num = [];
draw(show_num);
function dj() {
    draw(show_num);
    alert(show_num)
}

function draw(show_num) {
    var canvas_width = document.getElementById('canvas').clientWidth;
    var canvas_height = document.getElementById('canvas').clientHeight;
    var canvas = document.getElementById("canvas");//获取到canvas的对象，演员
    var context = canvas.getContext("2d");//获取到canvas画图的环境，演员表演的舞台
    canvas.width = canvas_width;
    canvas.height = canvas_height;
    var sCode = "A,B,C,E,F,G,H,J,K,L,M,N,P,Q,R,S,T,W,X,Y,Z,1,2,3,4,5,6,7,8,9,0,q,w,e,r,t,y,u,i,o,p,a,s,d,f,g,h,j,k,l,z,x,c,v,b,n,m";
    var aCode = sCode.split(",");
    var aLength = aCode.length;//获取到数组的长度

    for (var i = 0; i <= 3; i++) {
        var j = Math.floor(Math.random() * aLength);//获取到随机的索引值
        var deg = Math.random() * 30 * Math.PI / 180;//产生0~30之间的随机弧度
        var txt = aCode[j];//得到随机的一个内容
        show_num[i] = txt;
        var x = 10 + i * 20;//文字在canvas上的x坐标
        var y = 20 + Math.random() * 8;//文字在canvas上的y坐标
        context.font = "bold 23px 微软雅黑";

        context.translate(x, y);
        context.rotate(deg);

        context.fillStyle = randomColor();
        context.fillText(txt, 0, 0);

        context.rotate(-deg);
        context.translate(-x, -y);
    }
    for (var i = 0; i <= 5; i++) { //验证码上显示线条
        context.strokeStyle = randomColor();
        context.beginPath();
        context.moveTo(Math.random() * canvas_width, Math.random() * canvas_height);
        context.lineTo(Math.random() * canvas_width, Math.random() * canvas_height);
        context.stroke();
    }
    for (var i = 0; i <= 30; i++) { //验证码上显示小点
        context.strokeStyle = randomColor();
        context.beginPath();
        var x = Math.random() * canvas_width;
        var y = Math.random() * canvas_height;
        context.moveTo(x, y);
        context.lineTo(x + 1, y + 1);
        context.stroke();
    }

}
function randomColor() {//得到随机的颜色值
    var r = Math.floor(Math.random() * 256);
    var g = Math.floor(Math.random() * 256);
    var b = Math.floor(Math.random() * 256);
    return "rgb(" + r + "," + g + "," + b + ")";
}