ขีด จำกัด พื้นหลังที่กำหนดเองสำหรับโดนัท (เกจ)

//Gauge Plugin
(function() {
  if (!window.Chart) {
    return;
  }

  function GaugeChartHelper() {}
  GaugeChartHelper.prototype.setup = function(chart, config) {
    this.chart = chart;
    this.ctx = chart.ctx;
    this.limits = config.data.datasets[0].gaugeLimits;
    this.data = config.data.datasets[0].gaugeData;
    var options = chart.options;
    this.fontSize = options.defaultFontSize;
    this.fontStyle = options.defaultFontFamily;
    this.fontColor = options.defaultFontColor;
    this.ctx.textBaseline = "alphabetic";
    this.arrowAngle = 25 * Math.PI / 180;
    this.arrowColor = config.options.indicatorColor || options.arrowColor;
    this.showMarkers =
      typeof config.options.showMarkers === "undefined" ?
      true :
      config.options.showMarkers;
    if (config.options.markerFormatFn) {
      this.markerFormatFn = config.options.markerFormatFn;
    } else {
      this.markerFormatFn = function(value) {
        return value;
      };
    }
  };
  GaugeChartHelper.prototype.applyGaugeConfig = function(chartConfig) {
    this.calcLimits();
    chartConfig.data.datasets[0].data = this.doughnutData;
    var ctx = this.ctx;
    var labelsWidth = this.limits.map(
      function(label) {
        var text = this.markerFormatFn(label);
        return ctx.measureText(text).width;
      }.bind(this)
    );
    var padding = Math.max.apply(this, labelsWidth) + this.chart.width / 35;
    var heightRatio = this.chart.height / 50;
    chartConfig.options.layout.padding = {
      top: this.fontSize + heightRatio,
      left: padding,
      right: padding,
      bottom: heightRatio * 2
    };
  };
  GaugeChartHelper.prototype.calcLimits = function() {
    var limits = this.limits;
    var data = [];
    var total = 0;
    for (var i = 1, ln = limits.length; i < ln; i++) {
      var dataValue = Math.abs(limits[i] - limits[i - 1]);
      total += dataValue;
      data.push(dataValue);
    }
    this.doughnutData = data;
    var minValue = limits[0];
    var maxValue = limits[limits.length - 1];
    this.isRevers = minValue > maxValue;
    this.minValue = this.isRevers ? maxValue : minValue;
    this.totalValue = total;
  };
  GaugeChartHelper.prototype.updateGaugeDimensions = function() {
    var chartArea = this.chart.chartArea;
    this.gaugeRadius = this.chart.innerRadius;
    this.gaugeCenterX = (chartArea.left + chartArea.right) / 2;
    this.gaugeCenterY =
      (chartArea.top + chartArea.bottom + this.chart.outerRadius) / 2;
    this.arrowLength = this.chart.radiusLength * 2;
  };
  GaugeChartHelper.prototype.getCoordOnCircle = function(r, alpha) {
    return {
      x: r * Math.cos(alpha),
      y: r * Math.sin(alpha)
    };
  };
  GaugeChartHelper.prototype.getAngleOfValue = function(value) {
    var result = 0;
    var gaugeValue = value - this.minValue;
    if (gaugeValue <= 0) {
      result = 0;
    } else if (gaugeValue >= this.totalValue) {
      result = Math.PI;
    } else {
      result = Math.PI * gaugeValue / this.totalValue;
    }
    if (this.isRevers) {
      return Math.PI - result;
    } else {
      return result;
    }
  };
  GaugeChartHelper.prototype.renderLimitLabel = function(value) {
    var ctx = this.ctx;
    var angle = this.getAngleOfValue(value);
    var coord = this.getCoordOnCircle(
      this.chart.outerRadius + this.chart.radiusLength / 2,
      angle
    );
    var align;
    var diff = angle - Math.PI / 2;
    if (diff > 0) {
      align = "left";
    } else if (diff < 0) {
      align = "right";
    } else {
      align = "center";
    }
    ctx.textAlign = align;
    ctx.font = this.fontSize + "px " + this.fontStyle;
    ctx.fillStyle = this.fontColor;
    var text = this.markerFormatFn(value);
    ctx.fillText(
      text,
      this.gaugeCenterX - coord.x,
      this.gaugeCenterY - coord.y
    );
  };
  GaugeChartHelper.prototype.renderLimits = function() {
    for (var i = 0, ln = this.limits.length; i < ln; i++) {
      this.renderLimitLabel(this.limits[i]);
    }
  };
  GaugeChartHelper.prototype.renderValueLabel = function() {
    var label = this.data.value.toString();
    var ctx = this.ctx;
    ctx.font = "30px " + this.fontStyle;
    var stringWidth = ctx.measureText(label).width;
    var elementWidth = 0.75 * this.gaugeRadius * 2;
    var widthRatio = elementWidth / stringWidth;
    var newFontSize = Math.floor(30 * widthRatio);
    var fontSizeToUse = Math.min(newFontSize, this.gaugeRadius);
    ctx.textAlign = "center";
    ctx.font = fontSizeToUse + "px " + this.fontStyle;
    ctx.fillStyle = this.data.valueColor || this.fontColor;
    ctx.fillText(label, this.gaugeCenterX, this.gaugeCenterY);
  };
  GaugeChartHelper.prototype.renderValueArrow = function(value) {
    var angle = this.getAngleOfValue(
      typeof value === "number" ? value : this.data.value
    );
    this.ctx.globalCompositeOperation = "source-over";
    this.renderArrow(
      this.gaugeRadius,
      angle,
      this.arrowLength,
      this.arrowAngle,
      this.arrowColor
    );
  };
  GaugeChartHelper.prototype.renderSmallValueArrow = function(value) {
    var angle = this.getAngleOfValue(value);
    this.ctx.globalCompositeOperation = "source-over";
    this.renderArrow(
      this.gaugeRadius - 1,
      angle,
      this.arrowLength - 1,
      this.arrowAngle,
      this.arrowColor
    );
  };
  GaugeChartHelper.prototype.clearValueArrow = function(value) {
    var angle = this.getAngleOfValue(value);
    this.ctx.lineWidth = 2;
    this.ctx.globalCompositeOperation = "destination-out";
    this.renderArrow(
      this.gaugeRadius - 1,
      angle,
      this.arrowLength + 1,
      this.arrowAngle,
      "#FFFFFF"
    );
    this.ctx.stroke();
  };
  GaugeChartHelper.prototype.renderArrow = function(
    radius,
    angle,
    arrowLength,
    arrowAngle,
    arrowColor
  ) {
    var coord = this.getCoordOnCircle(radius, angle);
    var arrowPoint = {
      x: this.gaugeCenterX - coord.x,
      y: this.gaugeCenterY - coord.y
    };
    var ctx = this.ctx;
    ctx.fillStyle = arrowColor;
    ctx.beginPath();
    ctx.moveTo(arrowPoint.x, arrowPoint.y);
    coord = this.getCoordOnCircle(arrowLength, angle + arrowAngle);
    ctx.lineTo(arrowPoint.x + coord.x, arrowPoint.y + coord.y);
    coord = this.getCoordOnCircle(arrowLength, angle - arrowAngle);
    ctx.lineTo(arrowPoint.x + coord.x, arrowPoint.y + coord.y);
    ctx.closePath();
    ctx.fill();
  };
  GaugeChartHelper.prototype.animateArrow = function() {
    var stepCount = 30;
    var animateTimeout = 300;
    var gaugeValue = this.data.value - this.minValue;
    var step = gaugeValue / stepCount;
    var i = 0;
    var currentValue = this.minValue;
    var interval = setInterval(
      function() {
        i++;
        this.clearValueArrow(currentValue);
        if (i > stepCount) {
          clearInterval(interval);
          this.renderValueArrow();
        } else {
          currentValue += step;
          this.renderSmallValueArrow(currentValue);
        }
      }.bind(this),
      animateTimeout / stepCount
    );
  };
  Chart.defaults.tsgauge = {
    animation: {
      animateRotate: true,
      animateScale: false
    },
    cutoutPercentage: 95,
    rotation: Math.PI,
    circumference: Math.PI,
    legend: {
      display: false
    },
    scales: {},
    arrowColor: "#444"
  };
  Chart.controllers.tsgauge = Chart.controllers.doughnut.extend({
    initialize: function(chart) {
      var gaugeHelper = (this.gaugeHelper = new GaugeChartHelper());
      gaugeHelper.setup(chart, chart.config);
      gaugeHelper.applyGaugeConfig(chart.config);
      chart.config.options.animation.onComplete = function(chartElement) {
        gaugeHelper.updateGaugeDimensions();
        gaugeHelper.animateArrow();
      };
      Chart.controllers.doughnut.prototype.initialize.apply(this, arguments);
    },
    draw: function() {
      Chart.controllers.doughnut.prototype.draw.apply(this, arguments);
      var gaugeHelper = this.gaugeHelper;
      gaugeHelper.updateGaugeDimensions();
      gaugeHelper.renderValueLabel();
      if (gaugeHelper.showMarkers) {
        gaugeHelper.renderLimits();
      }
      gaugeHelper.renderSmallValueArrow(gaugeHelper.minValue);
    }
  });
})();

//Chart setup

var ctx = document.getElementById("chart3").getContext("2d");
new Chart(ctx, {
  type: "tsgauge",
  data: {
    datasets: [{
      backgroundColor: ["#0fdc63", "#0fdc63", "#fd9704", "#fd9704", "#fd9704", "#ff7143", "#ff7143"],
      borderWidth: 0,
      gaugeData: {
        value: 50,
        valueColor: "#ff7143"
      },
      gaugeLimits: [0, 20, 30, 40, 60, 70, 80, 100],
    }]
  },
  options: {
    events: [],
    showMarkers: true,
    markerFormatFn: n => n % 20 === 0 ? n.toString() : '',
  }
});

.gauge {
  width: 500px;
  height: 400px;
}

<link href="https://cdn.jsdelivr.net/npm/chart.js@2.9.2/dist/Chart.min.css" rel="stylesheet" />
<script src="https://cdn.jsdelivr.net/npm/chart.js@2.9.2/dist/Chart.bundle.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>


<div class="gauge">
  <canvas id="chart3"></canvas>
</div>