raspap-webgui/app/js/linkquality.js

// Link quality gauge for ChartJS

// Support for dark theme
theme = getCookie('theme');
if (theme == 'lightsout.css') {
  var borderColor = 'rgba(37, 153, 63, 1)';
  var labelColor = 'rgba(37, 153, 63, 1)';
} else if (theme == 'material-light.php') {
  var borderColor = '#f2f2fb';
  var labelColor = '#f2f2fb';
} else if (theme == 'material-dark.php') {
  var borderColor = '#f2f2fb';
  var labelColor = '#f2f2fb';
} else {
  var borderColor = 'rgba(147, 210, 162, 1)';
  var labelColor = 'rgba(130, 130, 130, 1)';
}

let data1 = {
  datasets: [{
    data: [linkQ, 100-linkQ],
    backgroundColor: 'transparent',
    borderColor: borderColor,
  }],
};

let config = {
  type: 'doughnut',
  data: data1,
  options: {
    aspectRatio: 2,
    responsive: true,
    maintainAspectRatio: false,
    tooltips: {enabled: false},
    hover: {mode: null},
    legend: {
      display: false,
    },
    rotation: (2/3)*Math.PI,//2+(1/3),
    circumference: (1+(2/3)) * Math.PI, // * Math.PI,
    cutoutPercentage: 80,
    animation: {
      animateScale: false,
      animateRotate: true
    },
    tooltips: {
      enabled: false
    }
  },
  centerText: {
    display: true,
    text: linkQ + "%"
  },
  plugins: [{
    beforeDraw: function(chart) {
      if (chart.config.centerText.display !== null &&
        typeof chart.config.centerText.display !== 'undefined' &&
        chart.config.centerText.display) {
          drawLinkQ(chart);
      }
    }
  }]
};

function drawLinkQ(chart) {

  let width = chart.chart.width;
  let height = chart.chart.height;
  let ctx = chart.chart.ctx;

  ctx.restore();
  let fontSize = (height / 100).toFixed(2);
  ctx.font = fontSize + "em sans-serif";
  ctx.fillStyle = labelColor;
  ctx.textBaseline = "middle";

  let text = chart.config.centerText.text;
  let textX = Math.round((width - ctx.measureText(text).width) * 0.5);
  let textY = height / 2;
  ctx.fillText(text, textX, textY);
  ctx.save();
}

window.onload = function() {
  let ctx = document.getElementById("divChartLinkQ").getContext("2d");
  var chart = new Chart(ctx, config);
};