<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, minimum-scale=1, user-scalable=no">
  <title>Canvas</title>
</head>
<body>
  <canvas id="canvas" width="300" height="300"></canvas>

  <script>
    draw(66);
    /**
     * [順時針方向畫圖，起始點(diǎn)在左側(cè)]
     * @param  {[number]} percent [所占的進(jìn)度百分比，比如66%，則傳66即可，0 <= percent <= 100]
     * @param  {[number]} sR      [圓弧起始角度，可不傳，默認(rèn)是π/2，Math.PI/2 <= sR < 3/2 * Math.PI]
     */
    function draw(percent, sR) {
      if (percent < 0 || percent > 100) {
        return;
      }
      if (sR < Math.PI/2 || sR >= 3/2 * Math.PI) {
        return;
      }

      var canvas = document.querySelector('#canvas'),
          cxt = canvas.getContext('2d'),
          cWidth = canvas.width,
          cHeight = canvas.height,
          baseColor = '#e1e1e1',
          coverColor = '#fe4d43',
          PI = Math.PI,
          sR = sR || 1/2 * PI; // 默認(rèn)圓弧的起始點(diǎn)弧度為π/2

      var finalRadian = sR + ((PI + (PI - sR) * 2) * percent / 100); // 紅圈的終點(diǎn)弧度
      var step = (PI + (PI - sR) * 2)/100; // 一個1%對應(yīng)的弧度大小
      var text = 0; // 顯示的數(shù)字
      var timer = setInterval(function() {
        cxt.clearRect(0, 0, cWidth, cHeight);
        var endRadian =  sR + text * step;
        // 畫灰色圓弧
        drawCanvas(cWidth/2, cHeight/2, 80, sR, sR + (PI + (PI - sR) * 2), baseColor, 2);
        // 畫紅色圓弧
        drawCanvas(cWidth/2, cHeight/2, 80, sR, endRadian, coverColor, 2);

        // 畫紅色圓頭
        // 紅色圓頭其實(shí)就是一個圓，關(guān)鍵的是找到其圓心，涉及到三角函數(shù)知識，自己畫個圖一看就明了
        var angle = 2*PI - endRadian; // 轉(zhuǎn)換成逆時針方向的弧度（三角函數(shù)中的）
        xPos = Math.cos(angle) * 80 + cWidth/2; // 紅色圓 圓心的x坐標(biāo)
        yPos = -Math.sin(angle) * 80 + cHeight/2; // 紅色圓 圓心的y坐標(biāo)
        drawCanvas(xPos, yPos, 2, 0, 2*PI, coverColor, 2);

        // 數(shù)字
        cxt.fillStyle = coverColor;
        cxt.font = '40px PT Sans';
        var textWidth = cxt.measureText(text+'%').width;
        cxt.fillText(text+'%', cWidth/2 - textWidth/2, cHeight/2 + 15);
        text++;

        if (endRadian.toFixed(2) >= finalRadian.toFixed(2)) {
          clearInterval(timer);
        }
      }, 30);

      function drawCanvas(x,y,r,sRadian,eRadian,color,lineWidth) {
        cxt.beginPath();
        cxt.lineCap = "round";
        cxt.strokeStyle = color;
        cxt.lineWidth = lineWidth;
        cxt.arc(x, y, r, sRadian, eRadian, false);
        cxt.stroke();
      }
    }
  </script>
</body>
</html>

關(guān)于動畫部分，可以使用requestAnimationFrame做優(yōu)化，函數(shù)改寫如下：

function draw(percent, sR) {
  if (percent < 0 || percent > 100) {
    return;
  }
  if (sR < Math.PI/2 || sR >= 3/2 * Math.PI) {
    return;
  }

  var canvas = document.querySelector('#canvas'),
      cxt = canvas.getContext('2d'),
      cWidth = canvas.width,
      cHeight = canvas.height,
      baseColor = '#e1e1e1',
      coverColor = '#fe4d43',
      PI = Math.PI,
      sR = sR || 1/2 * PI; // 默認(rèn)圓弧的起始點(diǎn)弧度為π/2

  var finalRadian = sR + ((PI + (PI - sR) * 2) * percent / 100); // 紅圈的終點(diǎn)弧度
  var step = (PI + (PI - sR) * 2)/100; // 一個1%對應(yīng)的弧度大小
  var text = 0; // 顯示的數(shù)字

  window.requestAnimationFrame(paint);
  function paint() {
    cxt.clearRect(0, 0, cWidth, cHeight);
    var endRadian =  sR + text * step;
    // 畫灰色圓弧
    drawCanvas(cWidth/2, cHeight/2, 80, sR, sR + (PI + (PI - sR) * 2), baseColor, 2);
    // 畫紅色圓弧
    drawCanvas(cWidth/2, cHeight/2, 80, sR, endRadian, coverColor, 2);

    // 畫紅色圓頭
    // 紅色圓頭其實(shí)就是一個圓，關(guān)鍵的是找到其圓心，涉及到三角函數(shù)知識，自己畫個圖一看就明了
    var angle = 2*PI - endRadian; // 轉(zhuǎn)換成逆時針方向的弧度（三角函數(shù)中的）
    xPos = Math.cos(angle) * 80 + cWidth/2; // 紅色圓 圓心的x坐標(biāo)
    yPos = -Math.sin(angle) * 80 + cHeight/2; // 紅色圓 圓心的y坐標(biāo)
    drawCanvas(xPos, yPos, 2, 0, 2*PI, coverColor, 2);

    // 數(shù)字
    cxt.fillStyle = coverColor;
    cxt.font = '40px PT Sans';
    var textWidth = cxt.measureText(text+'%').width;
    cxt.fillText(text+'%', cWidth/2 - textWidth/2, cHeight/2 + 15);
    text++;

    if (endRadian.toFixed(2) < finalRadian.toFixed(2)) {
      window.requestAnimationFrame(paint);
    }
  }

  function drawCanvas(x,y,r,sRadian,eRadian,color,lineWidth) {
    cxt.beginPath();
    cxt.lineCap = "round";
    cxt.strokeStyle = color;
    cxt.lineWidth = lineWidth;
    cxt.arc(x, y, r, sRadian, eRadian, false);
    cxt.stroke();
  }

到此這篇關(guān)于詳解JavaScript+Canvas繪制環(huán)形進(jìn)度條的文章就介紹到這了,更多相關(guān)JavaScript Canvas環(huán)形進(jìn)度條內(nèi)容請搜索腳本之家以前的文章或繼續(xù)瀏覽下面的相關(guān)文章希望大家以后多多支持腳本之家！

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