<script type="text/javascript" src="js/jquery-3.3.1.min.js" ></script>
<script>
    $(function(){
        var show_num = [];
        draw(show_num);

        $("#canvas").on('click',function(){
            draw(show_num);
        })
        $(".btn").on('click',function(){
            
 
var val = $(".input-val").val().toLowerCase();
            var num = show_num.join("");
            if(val==''){
                alert('請輸入驗證碼！');
            }else if(val == num){
                alert('提交成功！');
                $(".input-val").val('');
                // draw(show_num);

            }
 
else{
                alert('驗證碼錯誤！請重新輸入！');
                $(".input-val").val('');
                // draw(show_num);
            }
        })
    })

    //生成並渲染出驗證碼圖形
    function draw(show_num) {
        var canvas_width=$('#canvas').width();
        var canvas_height=$('#canvas').height();
        
 
var canvas = document.getElementById("canvas");//獲取到canvas的物件，演員
        var context = canvas.getContext("2d");//獲取到canvas畫圖的環境，演員表演的舞臺
        canvas.width = canvas_width;
        canvas.height = canvas_height;
        var sCode = "a,b,c,d,e,f,g,h,i,j,k,m,n,p,q,r,s,t,u,v,w,x,y,z,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;//獲取到陣列的長度
        
        for (var i = 0; i < 4; i++) {  //這裡的for迴圈可以控制驗證碼位數（如果想顯示6位數，4改成6即可）
            var j = Math.floor(Math.random() * aLength);//獲取到隨機的索引值
            // var deg = Math.random() * 30 * Math.PI / 180;//產生0~30之間的隨機弧度
            var deg = Math.random() - 0.5; //產生一個隨機弧度
            var txt = aCode[j];//得到隨機的一個內容
            show_num[i] = txt.toLowerCase();
            var x = 10 + i * 20;//文字在canvas上的x座標
            var y = 20 + Math.random() * 8;//文字在canvas上的y座標
            context.font = "bold 23px 微軟雅黑";

            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++) { //驗證碼上顯示線條
            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++) { //驗證碼上顯示小點
            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();
        }
    }

    //得到隨機的顏色值
    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 + ")";
    }

</script>