var tree = Hierarchy.FromNested(root, n => n.Children, out _)
.Sum(values);
var parts = Partition.Compute(tree,
new PartitionOptions { Width = 2 * Math.PI, Height = radius });
var arc = new ArcShape(parts.Y0[node], parts.Y1[node],
parts.X0[node], parts.X1[node]);
Arc.Write(ref sink, arc);
// d3.arc()(…), byte for byte, into SVG or native geometry