static/js/plugins/Chart.extension.js

//
// Chart extension for making the bars rounded
// Code from: https://codepen.io/jedtrow/full/ygRYgo
//

Chart.elements.Rectangle.prototype.draw = function() {

  var ctx = this._chart.ctx;
  var vm = this._view;
  var left, right, top, bottom, signX, signY, borderSkipped, radius;
  var borderWidth = vm.borderWidth;
  // Set Radius Here
  // If radius is large enough to cause drawing errors a max radius is imposed
  var cornerRadius = 6;

  if (!vm.horizontal) {
    // bar
    left = vm.x - vm.width / 2;
    right = vm.x + vm.width / 2;
    top = vm.y;
    bottom = vm.base;
    signX = 1;
    signY = bottom > top ? 1 : -1;
    borderSkipped = vm.borderSkipped || 'bottom';
  } else {
    // horizontal bar
    left = vm.base;
    right = vm.x;
    top = vm.y - vm.height / 2;
    bottom = vm.y + vm.height / 2;
    signX = right > left ? 1 : -1;
    signY = 1;
    borderSkipped = vm.borderSkipped || 'left';
  }

  // Canvas doesn't allow us to stroke inside the width so we can
  // adjust the sizes to fit if we're setting a stroke on the line
  if (borderWidth) {
    // borderWidth shold be less than bar width and bar height.
    var barSize = Math.min(Math.abs(left - right), Math.abs(top - bottom));
    borderWidth = borderWidth > barSize ? barSize : borderWidth;
    var halfStroke = borderWidth / 2;
    // Adjust borderWidth when bar top position is near vm.base(zero).
    var borderLeft = left + (borderSkipped !== 'left' ? halfStroke * signX : 0);
    var borderRight = right + (borderSkipped !== 'right' ? -halfStroke * signX : 0);
    var borderTop = top + (borderSkipped !== 'top' ? halfStroke * signY : 0);
    var borderBottom = bottom + (borderSkipped !== 'bottom' ? -halfStroke * signY : 0);
    // not become a vertical line?
    if (borderLeft !== borderRight) {
      top = borderTop;
      bottom = borderBottom;
    }
    // not become a horizontal line?
    if (borderTop !== borderBottom) {
      left = borderLeft;
      right = borderRight;
    }
  }

  ctx.beginPath();
  ctx.fillStyle = vm.backgroundColor;
  ctx.strokeStyle = vm.borderColor;
  ctx.lineWidth = borderWidth;

  // Corner points, from bottom-left to bottom-right clockwise
  // | 1 2 |
  // | 0 3 |
  var corners = [
    [left, bottom],
    [left, top],
    [right, top],
    [right, bottom]
  ];

  // Find first (starting) corner with fallback to 'bottom'
  var borders = ['bottom', 'left', 'top', 'right'];
  var startCorner = borders.indexOf(borderSkipped, 0);
  if (startCorner === -1) {
    startCorner = 0;
  }

  function cornerAt(index) {
    return corners[(startCorner + index) % 4];
  }

  // Draw rectangle from 'startCorner'
  var corner = cornerAt(0);
  ctx.moveTo(corner[0], corner[1]);

  for (var i = 1; i < 4; i++) {
    corner = cornerAt(i);
    nextCornerId = i + 1;
    if (nextCornerId == 4) {
      nextCornerId = 0
    }

    nextCorner = cornerAt(nextCornerId);

    width = corners[2][0] - corners[1][0];
    height = corners[0][1] - corners[1][1];
    x = corners[1][0];
    y = corners[1][1];

    var radius = cornerRadius;

    // Fix radius being too large
    if (radius > height / 2) {
      radius = height / 2;
    }
    if (radius > width / 2) {
      radius = width / 2;
    }

    ctx.moveTo(x + radius, y);
    ctx.lineTo(x + width - radius, y);
    ctx.quadraticCurveTo(x + width, y, x + width, y + radius);
    ctx.lineTo(x + width, y + height - radius);
    ctx.quadraticCurveTo(x + width, y + height, x + width - radius, y + height);
    ctx.lineTo(x + radius, y + height);
    ctx.quadraticCurveTo(x, y + height, x, y + height - radius);
    ctx.lineTo(x, y + radius);
    ctx.quadraticCurveTo(x, y, x + radius, y);

  }

  ctx.fill();
  if (borderWidth) {
    ctx.stroke();
  }
};