js绘制验证码

var show_num=[];
draw(show_num);

function draw(show_num) {
        var canvas_width = $('#canvas').width();
        var canvas_height = $('#canvas').height();
        var canvas = document.getElementById("canvas");
        var context = canvas.getContext("2d");
        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";
        var aCode = sCode.split(",");
        var aLength = aCode.length;
        for (var i = 0; i <= 3; i++) {
            var j = Math.floor(Math.random() * aLength);
            var deg = Math.random() * 30 * Math.PI / 180;
            var txt = aCode[j];
            show_num[i] = txt; //.toLowerCase()
            var x = 10 + i * 20;
            var y = 20 + Math.random() * 8;
            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++) {
            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++) { 
            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() {
        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 + ")";
    };