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绘制完整饼图.html
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绘制完整饼图.html
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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>绘制完整饼图</title>
<style>
canvas {
border: 1px solid #ccc;
display: block;
margin: 100px auto;
}
</style>
</head>
<body>
<canvas width="600" height="400">
</canvas>
<script>
var mycanvas = document.querySelector("canvas");
var ctx = mycanvas.getContext("2d");
//1.根据数据绘制饼状图
//2.绘制标题 从扇形的弧中心伸出一条线，再画一条再横线，再横线上面写文字标题
//3.在画布的左上角绘制说明，一个和扇形一样颜色的矩形，旁边就是文字说明
var pieChart = function(ctx){
this.ctx = ctx || document.querySelector("canvas").getContext("2d");
this.width = this.ctx.canvas.width;
this.height = this.ctx.canvas.height;
/*绘制饼图的中心*/
this.x0 = this.width / 2 + 60;
this.y0 = this.height / 2;
/*半径*/
this.radius = 150;
/*穿出圆那部分线的长度*/
this.outLine = 20;
/*说明矩形的大小*/
this.rectW = 30;
this.rectH = 16;
this.space = 20;
};
pieChart.prototype.init = function(data){
this.drawPie(data);
};
pieChart.prototype.drawPie = function(data){
var that = this;
/*1.转化为弧度*/
var new_data = this.transformAngle(data); //data添加多一个属性angle
/*1.绘制饼图*/
var startAngle = 0;
var endAngle = 0;
data.forEach( function(item, i) {
endAngle += item.angle;
that.ctx.beginPath();
that.ctx.moveTo(that.x0,that.y0);
that.ctx.arc(that.x0,that.y0,that.radius,startAngle,endAngle);
var color = that.randomColor();
that.ctx.fillStyle = color;
that.ctx.fill();
// 绘制标题
var title = item.title;
that.drawTitle(startAngle,item.angle,color,title);
startAngle += item.angle;
// 绘制说明
that.drawDesc(title,i);
});
};
pieChart.prototype.drawTitle = function(startAngle,angle,color,title){
/*1.通过圆心点-确定伸出去的线，通过伸出去的点-确定这个线*/
/*2.确定伸出去的点，需要确定伸出去的线的长度*/
/*3.固定伸出去的线的长度*/
/*4.计算每个圆弧的一半超出去的点坐标*/
/*5.公式:outX = (r + outLine) * cos(angle)/2
outY = (r + outLine) * sin(angle)/2
*/
var line = this.radius + this.outLine;
var lineX = line * Math.cos(startAngle + angle/2);
var lineY = line * Math.sin(startAngle + angle/2);
var outX = this.x0 + lineX;
var outY = this.y0 + lineY;
this.ctx.beginPath();
this.ctx.moveTo(this.x0,this.y0);
this.ctx.lineTo(outX,outY);
this.ctx.strokeStyle = color;
this.ctx.stroke();
/*画文字和下划线*/
/*线的方向怎么判断 伸出去的点在x0的左边，线的的方向就向左边*/
/*线的方向怎么判断 伸出去的点在x0的右边，线的的方向就向右边*/
/*获取文字长度*/
this.ctx.font="bold 15px Arial";
var textWidth = this.ctx.measureText(title).width;
this.ctx.beginPath();
this.ctx.moveTo(outX,outY);
if(outX > this.x0){
this.ctx.lineTo(outX+textWidth,outY);
this.ctx.textAlign = "left";
}else{
this.ctx.lineTo(outX-textWidth,outY);
this.ctx.textAlign = "right";
}
this.ctx.strokeStyle = color;
this.ctx.stroke();
this.ctx.textBaseline = 'bottom';
this.ctx.fillText(title,outX,outY);
};
pieChart.prototype.drawDesc = function(title,index){
this.ctx.fillRect(this.space,this.space + index * (this.rectH + 10),this.rectW,this.rectH);
/*绘制文字*/
this.ctx.beginPath();
this.ctx.textAlign = 'left';
this.ctx.textBaseline = 'top';
this.ctx.font = '12px Microsoft YaHei';
this.ctx.fillText(title,this.space + this.rectW + 10 , this.space + index * (this.rectH + 10));
};
//把data的数据转换为对应的弧度
pieChart.prototype.transformAngle = function(data){
var sum = 0;
data.forEach( function(item, i) {
sum += item.num;
});
data.forEach( function(item, i) {
item.angle = item.num / sum * Math.PI * 2;
});
return data;
};
pieChart.prototype.randomColor = function(){
var R = Math.floor(Math.random() * 256);
var G = Math.floor(Math.random() * 256);
var B = Math.floor(Math.random() * 256);
var RGB = "rgb("+R+","+G+","+B+")";
return RGB;
};
var data = [
{
title:'15-20岁',
num:50
},
{
title:'20-25岁',
num:30
},
{
title:'25-30岁',
num:60
},
{
title:'30岁以上',
num:8
}
]
var Pie = new pieChart();
Pie.init(data);
</script>
</body>
</html>