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Detailed explanation of the steps to dynamically implement pie charts in html5+canvas

php中世界最好的语言Original: 2018-05-07 17:45:393734browse

This time I will bring you a detailed explanation of the steps to dynamically implement a pie chart in html5 canvas. What are the precautions for dynamically implementing a pie chart in html5 canvas. Here are practical cases, let’s take a look.

Let’s look at the renderings first

##There is no reference to third-party libraries such as jquery, but only the

dom operation and the characteristics of canvas Written.

Canvas circle drawing is generally divided into solid circles and hollow circles.

According to the demand analysis, we know that the circle is a solid circle.

1. First use canvas to draw a solid circle

//伪代码
var canvas = document.createElement("canvas");
var ctx = canvas.getContext('2d');
ctx.beginPath();
ctx.arc(圆心x轴坐标,圆心y轴坐标,半径,开始角,结束角);
ctx.fillStyle = 'green';
ctx.closePath();
ctx.fill();

2. Draw a pie chart according to different colors

//伪代码
var canvas = document.createElement("canvas");
var ctx = canvas.getContext('2d');
ctx.beginPath();
ctx.arc(圆心x轴坐标,圆心y轴坐标,半径,绿色开始角,绿色结束角);
ctx.fillStyle = 'green';
ctx.closePath();
ctx.fill();
ctx.beginPath();
ctx.arc(圆心x轴坐标,圆心y轴坐标,半径,红色开始角,红色结束角);
ctx.fillStyle = 'red';
ctx.closePath();
ctx.fill();
ctx.beginPath();
ctx.arc(圆心x轴坐标,圆心y轴坐标,半径,黄色开始角,黄色结束角);
ctx.fillStyle = 'yellow';
ctx.closePath();
ctx.fill();
ctx.beginPath();
ctx.arc(圆心x轴坐标,圆心y轴坐标,半径,紫色开始角,紫色结束角);
ctx.fillStyle = 'purple';
ctx.closePath();
ctx.fill();

3.Dynamic drawing Pie chart

Three methods are generally recommended on the Internet for dynamically drawing circles: requestAnimationFrame, setInterval (timing), and dynamic angle calculation.

Here I use the first requestAnimationFrame method.

A problem was discovered during the writing process, that is, when dynamically drawing a circle, it is not drawn based on the coordinates of the center of the circle. In order to solve this problem, you need to redefine the coordinates of the canvas brush as the coordinates of the original circle center each time you draw a circle.

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title></title>
    <style>
        #graph {
/*            border: 1px solid black;
            height: 100%;
            width: 100%;
            box-sizing: border-box;*/
        }
    </style>
</head>
<body>
<p id="circle" style="width: 500px;float: left;"></p>
</body>
</html>
<script type="text/javascript">
(function(window,undefined){
    var data = [
        {"product":"产品1","sales":[192.44 ,210.54 ,220.84 ,230.11 ,220.85 ,210.59 ,205.49 ,200.55 ,195.71 ,187.46 ,180.66 ,170.90]},
        {"product":"产品2","sales":[122.41 ,133.16 ,145.65 ,158.00 ,164.84 ,178.62 ,185.70 ,190.13 ,195.53 ,198.88 ,204.32 ,210.91]},
        {"product":"产品3","sales":[170.30 ,175.00 ,170.79 ,165.10 ,165.62 ,160.92 ,155.92 ,145.77 ,145.17 ,140.27 ,135.99 ,130.33]},
        {"product":"产品4","sales":[165.64 ,170.15 ,175.10 ,185.32 ,190.90 ,190.01 ,187.05 ,183.74 ,177.24 ,181.90 ,179.54 ,175.98]}
    ]
        
    var dom_circle = document.getElementById('circle');
    if(dom_circle != undefined && dom_circle != null)
    {
        var canvas = document.createElement("canvas");
        dom_circle.appendChild(canvas);
        var ctx = canvas.getContext('2d');
        var defaultStyle = function(Dom,canvas){
            if(Dom.clientWidth <= 300)
            {
                canvas.width = 300;
                Dom.style.overflowX = "auto";
            }
            else{
                canvas.width = Dom.clientWidth;
            }
            if(Dom.clientHeight <= 300)
            {
                canvas.height = 300;
                Dom.style.overflowY = "auto";
            }
            else
            {
                canvas.height = Dom.clientHeight;
            }
            //坐标轴区域
            //注意，实际画折线图区域还要比这个略小一点
            return {
                p1:&#39;green&#39;,
                p2:&#39;red&#39;,
                p3:&#39;yellow&#39;,
                p4:&#39;purple&#39;,
                x: 0 ,    //坐标轴在canvas上的left坐标
                y: 0 ,    //坐标轴在canvas上的top坐标
                maxX: canvas.width ,   //坐标轴在canvas上的right坐标
                maxY: canvas.height ,   //坐标轴在canvas上的bottom坐标
                r:(canvas.width)/2,  //起点
                ry:(canvas.height)/2,  //起点
                cr: (canvas.width)/4, //半径
                startAngle:-(1/2*Math.PI),               //开始角度
                endAngle:(-(1/2*Math.PI)+2*Math.PI),     //结束角度
                xAngle:1*(Math.PI/180)                   //偏移量
            };
        }
        //画圆
        var tmpAngle = -(1/2*Math.PI);
        var ds = null;
        var sum = data[0][&#39;sales&#39;][0]+data[0][&#39;sales&#39;][1]+data[0][&#39;sales&#39;][2]+data[0][&#39;sales&#39;][3]
        var percent1 = data[0][&#39;sales&#39;][0]/sum * Math.PI * 2 ;
        var percent2 = data[0][&#39;sales&#39;][1]/sum * Math.PI * 2 + percent1;
        var percent3 = data[0][&#39;sales&#39;][2]/sum * Math.PI * 2 + percent2;
        var percent4 = data[0][&#39;sales&#39;][3]/sum * Math.PI * 2 + percent3;
        console.log(percent1);
        console.log(percent2);
        console.log(percent3);
        console.log(percent4);
        var tmpSum = 0;
        var drawCircle = function(){
            
            
            if(tmpAngle >= ds.endAngle)
            {
                return false;
            }
            else if(tmpAngle+ ds.xAngle > ds.endAngle)
            {
                tmpAngle = ds.endAngle;
            }
            else{
                tmpAngle += ds.xAngle;
                tmpSum += ds.xAngle
            }
            // console.log(ds.startAngle+'***'+tmpAngle);
            // console.log(tmpSum);
            // ctx.clearRect(ds.x,ds.y,canvas.width,canvas.height);
            
            if(tmpSum > percent1 && tmpSum <percent2)
            {
                ctx.beginPath();
                ctx.moveTo(ds.r,ds.ry);
                ctx.arc(ds.r,ds.ry,ds.cr,ds.startAngle+percent1,tmpAngle);
            
                ctx.fillStyle = ds.p2;
            }
            else if(tmpSum > percent2 && tmpSum <percent3)
            {
                ctx.beginPath();
                ctx.moveTo(ds.r,ds.ry);
                ctx.arc(ds.r,ds.ry,ds.cr,ds.startAngle+percent2,tmpAngle);
                ctx.fillStyle = ds.p3;
            }
            else if(tmpSum > percent3 )
            {
                ctx.beginPath();
                ctx.moveTo(ds.r,ds.ry);
                ctx.arc(ds.r,ds.ry,ds.cr,ds.startAngle+percent3,tmpAngle);
                ctx.fillStyle = ds.p4;
            }
            else{
                ctx.beginPath();
                ctx.moveTo(ds.r,ds.ry);
                ctx.arc(ds.r,ds.ry,ds.cr,ds.startAngle,tmpAngle);
                ctx.fillStyle = ds.p1;
            }
            ctx.closePath();
            ctx.fill();
            requestAnimationFrame(drawCircle);
        }
        this.toDraw = function(){
            ds= defaultStyle(dom_circle,canvas);
            // console.log(tmpAngle);
            // console.log(ds.xAngle)
            ctx.clearRect(ds.x,ds.y,canvas.width,canvas.height);
            drawCircle();
        }
        this.toDraw();
        var self = this;
        window.onresize = function(){
            self.toDraw()
        }
    }
})(window);    
</script>

I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the php Chinese website!

Detailed explanation of the steps to dynamically implement pie charts in html5+canvas

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