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HTML5动画(二):Canvas 实现圆形进度条并显示数字百分比

实现效果

技术分享

1.首先创建html代码

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

2.创建canvas环境

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 

3.绘制5像素宽的运动外圈

//绘制5像素宽的运动外圈        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();        }

 4.绘制白色外圈

//绘制白色外圈        function whiteCircle(){            context.save();            context.beginPath();            context.lineWidth = 2; //设置线宽            context.strokeStyle = "red";            context.arc(centerX, centerY, 100 , 0, Math.PI*2, false);            context.stroke();            context.closePath();            context.restore();        }  

5.百分比文字绘制

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();        } 

6.让它运动起来

//动画循环        (function drawFrame(){            window.requestAnimationFrame(drawFrame);            context.clearRect(0, 0, canvas.width, canvas.height);            whiteCircle();            text(speed);            blueCircle(speed);            if(speed > 100) speed = 0;            speed += 0.1;        }());

完整代码

<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>HTML5 Canvas 圆形进度条并显示数字百分比</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5像素宽的运动外圈        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.lineWidth = 2; //设置线宽            context.strokeStyle = "red";            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);            context.clearRect(0, 0, canvas.width, canvas.height);            whiteCircle();            text(speed);            blueCircle(speed);            if(speed > 100) speed = 0;            speed += 0.1;        }());    }</script></body></html>

 

HTML5动画(二):Canvas 实现圆形进度条并显示数字百分比