技术教程 编程教程 canvas 绘制圆形进度条 正文

canvas 绘制圆形进度条

2023-05-25,,

<!DOCTYPE html>

<html lang="en">

<head>

    <meta charset="UTF-8">

    <title>canvas 圆形进度条效果</title>

    <style>

    *{margin:0;padding:0;}

    body{text-align:center;background-color:#000;}

    </style>

</head>

<body>

    <canvas id="canvas" width="500" height="500" style="background:#000;"></canvas>

    <script>

        window.onload = function(){

            var canvas = document.getElementById('canvas'),  //获取canvas元素

                context = canvas.getContext('2d'),  //获取画图环境，指明为2d

                centerX = canvas.width/2,   //Canvas中心点x轴坐标

                centerY = canvas.height/2,  //Canvas中心点y轴坐标

                rad = Math.PI*2/100, //将360度分成100份，那么每一份就是rad度

                speed = 0.1; //加载的快慢就靠它了

            //绘制蓝色外圈

            function blueCircle(n){

                context.save();

                context.strokeStyle = "#fff"; //设置描边样式

                context.lineWidth = 5; //设置线宽

                context.beginPath(); //路径开始

                context.arc(centerX, centerY, 100 , -Math.PI/2, -Math.PI/2 +n*rad, false); //用于绘制圆弧context.arc(x坐标，y坐标，半径，起始角度，终止角度，顺时针/逆时针)

                context.stroke(); //绘制

                context.closePath(); //路径结束

                context.restore();

            }

            //绘制白色外圈

            function whiteCircle(){

                context.save();

                context.beginPath();

                context.strokeStyle = "white";

                context.arc(centerX, centerY, 100 , 0, Math.PI*2, false);

                context.stroke();

                context.closePath();

                context.restore();

            }

            //百分比文字绘制

            function text(n){

                context.save(); //save和restore可以保证样式属性只运用于该段canvas元素

                context.strokeStyle = "#fff"; //设置描边样式

                context.font = "40px Arial"; //设置字体大小和字体

                //绘制字体，并且指定位置

                context.strokeText(n.toFixed(0)+"%", centerX-25, centerY+10);

                context.stroke(); //执行绘制

                context.restore();

            }

            //动画循环

            (function drawFrame(){

                window.requestAnimationFrame(drawFrame, canvas);

                context.clearRect(0, 0, canvas.width, canvas.height);

                whiteCircle();

                text(speed);

                blueCircle(speed);

                if(speed > 100) speed = 0;

                speed += 0.1;

            }());

        }

    </script>

</body>

</html>

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《canvas 绘制圆形进度条.doc》

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