利用canvas实现环形进度条

2020-01-05 06:57栏目:大国科技
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本港台现场报码 1

本港台现场报码,前提:有时候在项目中会有用到进度条的情况,使用css3也可以实现,但是对于性能不好的设备,或者网络不好的情况下,卡顿现象非常明显,避免出现不流畅的尴尬情况,所以记录一下,使用canvas来实现的方法。

效果图:

DOM中,首先定义canvas画板元素:

canvas width="500" height="500"  pyou browser not support canvas!/p /canvas

对于不支持canvas的浏览器则会显示:you browser not support canvas!

接下来是js编写:定义canvas.js并在页面引入

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.beginPath(); context.strokeStyle = "#49f"; context.lineWidth = 12; context.arc(centerX, centerY, 100, -Math.PI / 2, -Math.PI / 2 + n * rad, false); context.stroke(); context.restore();}//绘制白色外圈function whiteCircle() { context.save(); context.beginPath(); context.strokeStyle = "#A5DEF1"; context.lineWidth = 12; 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(); context.fillStyle = "#F47C7C"; context.font = "40px Arial"; context.textAlign = "center"; context.textBaseline = "middle"; context.fillText(n.toFixed(0) + "%", centerX, centerY); 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;}());window.requestAnimationFrame(drawFrame, canvas);

每行代码的注释标注非常清楚,如果还有不理解的可以去看canvas基础,应该就可以了。

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