HTML5 Canvas饼图

Question

我正在尝试创建一个简单的饼图,如下图所示:

该图表将显示测验的结果,用户可以选择a,b或c.它们是10个问题,用户每个问题只能选择一个选项.

我想要做的是通过传递a,b或c的值来显示饼图,每个段是100%的百分比.

到目前为止,我有以下内容:

var greenOne = "#95B524";
var greenTwo = "#AFCC4C";
var greenThree = "#C1DD54";

function CreatePieChart() {
  var chart = document.getElementById('piechart');
  var canvas = chart.getContext('2d');
  canvas.clearRect(0, 0, chart.width, chart.height);

  var total = 100;

  var a = 3;
  var b = 4;
  var c = 3;

  for (var i = 0; i < 3; i++) {
    canvas.fillStyle = "#95B524";
    canvas.beginPath();
    canvas.strokeStyle = "#fff";
    canvas.lineWidth = 3;
    canvas.arc(100, 100, 100, 0, Math.PI * 2, true);
    canvas.closePath();
    canvas.stroke();
    canvas.fill();
  }
}
CreatePieChart();

<canvas id="piechart" width="200" height="200"></canvas>

颜色特定于段的大小,因此绿色用于最大,绿色用于最小.

谢谢

Answer 1

即使在搜索谷歌并三重检查我的弧度值等之后,我仍然遇到这个问题,所以我创建了一个jsFiddle供人们玩,作为一个实例,并将发布下面的代码.

var canvas = document.getElementById("can");
var ctx = canvas.getContext("2d");
var lastend = 0;
var data = [200, 60, 15]; // If you add more data values make sure you add more colors
var myTotal = 0; // Automatically calculated so don't touch
var myColor = ['red', 'green', 'blue']; // Colors of each slice

for (var e = 0; e < data.length; e++) {
  myTotal += data[e];
}

for (var i = 0; i < data.length; i++) {
  ctx.fillStyle = myColor[i];
  ctx.beginPath();
  ctx.moveTo(canvas.width / 2, canvas.height / 2);
  // Arc Parameters: x, y, radius, startingAngle (radians), endingAngle (radians), antiClockwise (boolean)
  ctx.arc(canvas.width / 2, canvas.height / 2, canvas.height / 2, lastend, lastend + (Math.PI * 2 * (data[i] / myTotal)), false);
  ctx.lineTo(canvas.width / 2, canvas.height / 2);
  ctx.fill();
  lastend += Math.PI * 2 * (data[i] / myTotal);
}

<canvas id="can" width="200" height="200" />

Answer 2

我喜欢上一个答案，但是我觉得它缺乏代码清晰度，并且没有真正涵盖如何使用标签。

我将值移到数据对象数组中以便于声明。我将其他值（例如百分比）明确声明为数据对象的属性或单独的变量。我认为，这更易于阅读。

如果您对此感兴趣，那么重构也使将值绑定到输入框变得更加容易。

要了解我的意思并使用这些值，请查看此CodePen：http ://codepen.io/zfrisch/pen/pRbZeb

  var data = [{
    label: "one",
    value: 100,
    color: 'white'
  }, {
    label: "two",
    value: 100,
    color: 'skyBlue'
  }, {
    label: "three",
    value: 100,
    color: 'yellow'
  }];

  var total = 0;
  for (obj of data) {
    total += obj.value;
  }

  var canvas = document.getElementById('myCanvas');
  var ctx = canvas.getContext('2d');
  var previousRadian;
  var middle = {
    x: canvas.width / 2,
    y: canvas.height / 2,
    radius: canvas.height / 2,
  };
  
   //background
  ctx.beginPath();
  ctx.arc(middle.x, middle.y, middle.radius, 0, 2 * Math.PI);
  ctx.closePath();
  ctx.stroke();
  ctx.fillStyle = "black";
  ctx.fill();
   //end of background

  for (obj of data) {
    previousRadian = previousRadian || 0;
    obj.percentage = parseInt((obj.value / total) * 100)
    
    ctx.beginPath();
    ctx.fillStyle = obj.color;
    obj.radian = (Math.PI * 2) * (obj.value / total);
    ctx.moveTo(middle.x, middle.y);
    //middle.radius - 2 is to add border between the background and the pie chart
    ctx.arc(middle.x, middle.y, middle.radius - 2, previousRadian, previousRadian + obj.radian, false);
    ctx.closePath();
    ctx.fill();
    ctx.save();
    ctx.translate(middle.x, middle.y);
    ctx.fillStyle = "black";
    ctx.font = middle.radius / 10 + "px Arial";
    ctx.rotate(previousRadian + obj.radian);
    var labelText = "'" + obj.label + "' " + obj.percentage  + "%";
    ctx.fillText(labelText, ctx.measureText(labelText).width / 2, 0);
    ctx.restore();

    previousRadian += obj.radian;
  }

<canvas id="myCanvas" width="500" height="500" ></canvas>