使用canvas绘制一个简单的饼图
2019-04-19 本文已影响0人
李华炎
本案例为书本的一个例子。
该地址为书本代码链接： https://github.com/ikcamp/Efficient-Mobile-Web-FE-Development/
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width,initial-scale=1,user-scalable=no"/>
<meta content="telephone=no" name="format-detection"/>
<meta content="address=no" name="format-detection"/>
<meta name="msapplication-tap-highlight" content="no" />
<title>使用Canvas绘制一个简单的饼图</title>
</head>
<body>
<canvas class="pie-chart" width="850" height="500" style="transform: scale(0.5);transform-origin: 0 0"></canvas>
<script type="text/javascript">
let PieChart = function(selector, options) {
let canvas = "string" === typeof selector ? document.querySelector(selector) : null;
if(canvas === null) return false;
let defaultOptions = {
radius: 200,
legendParms: {
font: "24px Arial",
x: 30,
y: 30,
margin: 50,
width: 40,
height: 24
}
}
this.context = canvas.getContext("2d");
this.width = canvas.getAttribute("width") || 300;
this.height = canvas.getAttribute("height") || 300;
this.options = Object.assign(defaultOptions, options);
};
PieChart.prototype.load = function(data) {
data.forEach(item => this.count ? this.count += item.value : this.count = item.value);
this.data = data;
return this;
};
PieChart.prototype.render = function() {
let _generateLegend = (item, index) => {
this.context.fillRect(
this.options.legendParms.x,
this.options.legendParms.y + index * this.options.legendParms.margin,
this.options.legendParms.width,
this.options.legendParms.height
);
this.context.font = this.options.legendParms.font;
this.context.fillText(
item.title,
this.options.legendParms.y + this.options.legendParms.margin,
(index + 1) * this.options.legendParms.margin
);
};
let temparc = 0;
this.data.forEach((item, index) => {
item.color = `#${('00000'+(Math.random()*0x1000000<<0).toString(16)).substr(-6)}`;
this.context.beginPath();
this.context.moveTo(this.width / 2, this.height / 2);
let startarc = temparc, endarc = startarc + (item.value / this.count) * Math.PI * 2;
this.context.arc(
this.width / 2,
this.height / 2,
this.options.radius,
startarc,
endarc,
false
);
this.context.closePath();
this.context.fillStyle = item.color;
this.context.fill();
temparc = endarc;
if (this.options.legend) {
_generateLegend(item, index);
}
});
return this;
};
const data = [
{title: "沪江网校", value: 1024},
{title: "沪江小D", value: 512},
{title: "沪江学习", value: 256},
{title: "开心词场", value: 920}
];
let pie = new PieChart(".pie-chart", {legend: true});
pie.load(data).render();
</script>
</body>
</html>
