Custom d3 path generation

Demonstration of some odd behaviour of d3-shape's linkTo and arc.

The diagrams are generated from the same set of coordinates run through a function that generates variations on paths; for any line from (x0,y0) to (x1,y1), the options are:

curved: uses one of d3's link functions, linkHorizontal, linkVertical or linkRadial;
direct: straight line;
l_shape and l_shape_alt: an L-shaped line, or an arc and straight line if using radial coordinates;
dogleg and dogleg_alt: a dogleg, or in radial charts, arc-straight line-arc or straight line-arc-straight line.

The diagrams demonstrate the odd behaviour of the linkTo and arc commands when used in sequence. The uncorrected radial charts demonstrate the default behaviour, and the corrected charts have -0.5 Pi radians applied to the angles, i.e. for a line from a to b:

Uncorrected

context.arc(0, 0, b.y, a.x, b.x);

Corrected

context.arc(0, 0, b.y, a.x - Math.PI*0.5, b.x - Math.PI*0.5);

<!DOCTYPE html>
<head>
    <title>Custom paths going off track</title>
  <meta charset="utf-8">
  <script src="https://d3js.org/d3.v5.min.js"></script>
  <script src="d3-shape.js"></script>
  <script src="diagonal-mixin.js"></script>
  <style>
.testBox {
  float: left;
  width: 300px;
  margin: 0 0 24px 24px;
  padding: 10px;
  border: 1px solid #ccc;
  text-align: center;
}
path {
  fill: none;
  stroke: #555;
  stroke-width: 1px;
}
.node {
  stroke-width: 1px;
  stroke: #999;
}
.node.n_0 {
  fill: steelblue;
}
.node.n_1 {
  fill: deepskyblue;
}
.node.n_2 {
  fill: aliceblue;
}
.node.n_3 {
  fill: steelblue;
}
.radius {
  fill: none;
  stroke: #999;
  stroke-width: 1px;
  stroke-opacity: 0.5;
}
.radius:hover {
  stroke-opacity: 1;
}
  </style>
</head>
<body>
<h2>Custom path generation</h2>
<div id="test"></div>

var lineGen = dc.diagonalMixin(dc.orientationMixin(dc.radialLayoutMixin({
    _d3: {},
    uncorrected: false
  })));

lineGen.diagonal('curved');
  var points = [{
    x: 2.5871939500151235,
    y: 156
  },
  {
    x: 2.5871939500151235,
    y: 104
  },
  {
    x: 3.9916706657376197,
    y: 62
  },
  {
    x: 2.646329811729755,
    y: 0
  }];

var pt_arr = [1, 2, 3].map(function(e, i) {
    return { source: points[i], target: points[e] };
  });

[true, true, false].forEach(function(b, i) {
    if (!b) {
      points.forEach(p => {
        p.x = p.x * 180 / Math.PI;
      });
    }
    lineGen.radialLayout(b);
    lineGen.uncorrected = (i === 1);

['curved'].concat(Object.keys(dc.link.path)).forEach(function(l) {
      lineGen.diagonal(l);

var div = d3.select('#test')
        .append('div')
        .classed('testBox', true);

div.append('h5')
        .text(l + '; ' + (b ?
          (lineGen.uncorrected ? 'uncorrected ' : 'corrected ') + 'radial' :
          'cartesian'));

var g = div
        .append('svg')
        .attr('width', 280)
        .attr('height', 250)
        .append('g')
        .attr('transform', function() {
          return b ? 'translate(130,90)' : 'translate(-90,60)'
        });

g.selectAll('path')
        .data(pt_arr)
        .enter()
        .append("path")
        .attr("class", 'cluster-link')
        .attr("d", function(d) {
          return lineGen._d3.diagonal(d);
        });
      g.selectAll('circle.node')
        .data(points)
        .enter()
        .append('circle')
        .attr('r', 5)
        .attr('class', function(d, i) {
          return 'node ' + 'n_' + i
        })
        .attr('transform', function(d) {
          return b ?
            "translate(" + d3.pointRadial(d.x, d.y) + ")" :
            "translate(" + d.x + "," + d.y + ")"
        })
        .append('title')
        .text(function(d, i) { return i });

if (b) {
        g.selectAll('circle.radius')
          .data(pt_arr)
          .enter()
          .append('circle')
          .attr('class', 'radius')
          .attr('fill', 'none')
          .attr('r', function(d) {
            return d.source.y
          });
      }
    });
  });
}
go();
</script>
</body>
</html>

https://d3js.org/d3.v5.min.js