用H5 Canvas绘制一个仪表盘笔记

前端有许多做数据可视化的图表插件，但有时候UI设计的图可能用现成的js插件无法定制或者比较麻烦（还不如自己造轮子来的快）。
下面记录下用H5 canvas设计一个仪表盘代码：
<!DOCTYPE html>

<html lang="en">

 <head>

  <meta charset="UTF-8">

  <meta name="Generator" content="EditPlus">

  <meta name="Author" content="">

  <meta name="Keywords" content="">

  <meta name="Description" content="">

  <title>Document</title>

  <script src="tween.umd.min.js"></script>

  <style>

    .container {

       position: absolute;

       top: 40px;

       left: 100px;

       width: 138px;

       height: 138px;

       display: flex;

       align-items: center;

       justify-content: center;

    }

    #bg, #ring {

       position: absolute;

       width: 138px;

       height: 138px;

    }

    #bg {

       background-color: #fff;

    }

  </style>

 </head>

 <body style="background-color: #ccc">

    <div class="container">

        <div id="percent" style="z-index: 100; color: #fff;">0%</div>

        <canvas id="bg" width="138" height="138"></canvas>

        <canvas id="ring" width="138" height="138"></canvas>

    </div>

 </body>

 <script>

 const bgCanvas = document.querySelector('#bg');

 const ringCanvas = document.querySelector('#ring');

 const bgCtx = bgCanvas.getContext('2d');

 const ctx = ringCanvas.getContext('2d');

 const percentEl = document.querySelector('#percent');

 const pixelRatio = window.devicePixelRatio;

 const BG_RING_WIDTH = 6;

 const POINTER_BALL_RADIUS = 6;

 const CANVAS_WIDTH = 138;

 const CANVAS_HEIGHT = 138;

 const INNER_CIRCLE_RADIUS = 45;

 if(pixelRatio > 1) {

     bgCanvas.width = CANVAS_WIDTH * 2;

     bgCanvas.height = CANVAS_HEIGHT * 2;

     ringCanvas.width = CANVAS_WIDTH * 2;

     ringCanvas.height = CANVAS_HEIGHT * 2;

     bgCanvas.style.width = CANVAS_WIDTH;

     bgCanvas.style.height = CANVAS_HEIGHT;

     ringCanvas.style.width = CANVAS_WIDTH;

     ringCanvas.style.height = CANVAS_HEIGHT;

 }

 function createBgCircle() {

    bgCtx.save();

    bgCtx.beginPath();

    bgCtx.arc(CANVAS_WIDTH / 2, CANVAS_HEIGHT / 2, INNER_CIRCLE_RADIUS, 0, 2 * Math.PI);

    let gradient = bgCtx.createLinearGradient(INNER_CIRCLE_RADIUS * 2, 0, 0, INNER_CIRCLE_RADIUS * 2);

    gradient.addColorStop(0, '#E69908');

    gradient.addColorStop(1, '#FDF27B');

    bgCtx.fillStyle = gradient;

    bgCtx.fill();

    bgCtx.restore();

 }

 function createBgRing() {

    bgCtx.save();

    bgCtx.beginPath();

    const x = CANVAS_WIDTH / 2;

    const y = r = x;

    bgCtx.arc(x, y, r, 0, 2 * Math.PI, true);

    bgCtx.arc(x, y, x - BG_RING_WIDTH, 0, 2 * Math.PI, false);

    bgCtx.fillStyle = '#EEF5F5';

    bgCtx.fill();

    bgCtx.restore();

 }

let imageLoaded = false;

let img = null;

 async function createProcessRing(radian) {

    const x = CANVAS_WIDTH / 2;

    const y = r = x;

    //裁剪扇形区域

    ctx.save();

    ctx.beginPath();

    ctx.moveTo(x, y);

    ctx.arc(x, y, r, -Math.PI/2, -Math.PI/2 + radian);

    ctx.clip();

    if(imageLoaded) {

        ctx.drawImage(img, 0, 0, img.width, img.height);

        ctx.restore();

        return;

    }

    return new Promise(resolve => {

        const imgUrl = "ring.png";

        img = new Image();

        img.src = imgUrl;

        img.onload = function() {

            imageLoaded = true;

            ctx.drawImage(img, 0, 0, img.width, img.height);

            ctx.restore();

            resolve();

        }

    })

 }

 function createBallPointer(x, y) {

    const cx = CANVAS_WIDTH / 2;

    const cy = cx;

    ctx.save();

    ctx.translate(cx, cy);

    ctx.beginPath();

    ctx.arc(x, y, POINTER_BALL_RADIUS, 0, 2 * Math.PI);

    let gradient = ctx.createLinearGradient(0, POINTER_BALL_RADIUS * 2, POINTER_BALL_RADIUS * 2, 0);

    gradient.addColorStop(0, '#FF8B00');

    gradient.addColorStop(1, '#F2C008');

    ctx.fillStyle = gradient;

    ctx.fill();

    ctx.restore();

 }

 function createAnimation(startAngle = 0, endAngle = 360, callback) {

    function animate(time) {

        requestAnimationFrame(animate)

        TWEEN.update(time)

    }

    requestAnimationFrame(animate)

    const p = {angle: startAngle}

    const tween = new TWEEN.Tween(p)

        .to({angle: endAngle}, 600)

        .easing(TWEEN.Easing.Quadratic.Out)

        .onUpdate(() => {

            let radian = Math.PI / 180 * p.angle;

            let x = (CANVAS_WIDTH / 2 - BG_RING_WIDTH) * Math.cos(Math.PI/2 - radian);

            let y = -(CANVAS_HEIGHT / 2 - BG_RING_WIDTH) * Math.sin(Math.PI/2 - radian);

            ctx.clearRect(0, 0, ringCanvas.width, ringCanvas.height);

            createProcessRing(radian);

            createBallPointer(x, y);

            percentEl.innerText = Math.round(p.angle / 360 * 100) + '%';

         })

         .start();

 }

 async function setup() {

    createBgCircle();

    createBgRing();

    await createProcessRing();

    createBallPointer(0, -(CANVAS_WIDTH / 2 - BG_RING_WIDTH/2));

    createAnimation(0, 360);

 }

setup();

 </script>

</html>
效果：
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用H5 Canvas绘制一个仪表盘笔记

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