d3-dag/src/zherebko/index.js

Layout algorithms for visualizing directed acylic graphs.

// Compute a zherebko layout for a dag assigning each node an x and y
// coordinate, and optionally assigning each link a points field with the x and
// y coordinates for intermediary stops on the edge.
import greedy from "./greedy";

export default function() {
  let width = 1;
  let height = 1;
  let indexer = greedy();

  function zherebko(dag) {
    // Topological Sort
    const ordered = [];
    dag.eachBefore((node, i) => {
      node.layer = i;
      ordered.push(node);
    });
    const maxLayer = ordered.length - 1;
    if (maxLayer === 0) {
      // center if only one node
      const [node] = ordered;
      node.x = width / 2;
      node.y = height / 2;
    } else {
      // Get indices
      indexer(ordered);

      // Map to coordinates
      let minIndex = 0;
      let maxIndex = 0;
      dag.eachLinks(({ data }) => {
        minIndex = Math.min(minIndex, data.index);
        maxIndex = Math.max(maxIndex, data.index);
      });
      if (minIndex === maxIndex) {
        // === 0
        // Center if graph is a line
        minIndex = -1;
        maxIndex = 1;
      }
      dag.each((node) => {
        node.x = (-minIndex / (maxIndex - minIndex)) * width;
        node.y = (node.layer / maxLayer) * height;
      });
      dag.eachLinks(({ source, target, data }) => {
        const points = [{ x: source.x, y: source.y }];

        const x = ((data.index - minIndex) / (maxIndex - minIndex)) * width;
        const y1 = ((source.layer + 1) / maxLayer) * height;
        const y2 = ((target.layer - 1) / maxLayer) * height;
        if (target.layer - source.layer === 2) {
          points.push({ x: x, y: y1 });
        } else if (target.layer - source.layer > 2) {
          points.push({ x: x, y: y1 }, { x: x, y: y2 });
        }

        points.push({ x: target.x, y: target.y });
        data.points = points;
      });
    }
    return dag;
  }

  zherebko.size = function(x) {
    return arguments.length
      ? (([width, height] = x), zherebko)
      : [width, height];
  };

  return zherebko;
}