dagre-react-flow

Dagre with React Flow

Dagre is a JavaScript library for laying out directed graphs. It computes optimal node positions for hierarchical/tree layouts. React Flow handles rendering; dagre handles positioning.

Quick Start

pnpm add @dagrejs/dagre

import dagre from '@dagrejs/dagre';
import { Node, Edge } from '@xyflow/react';

const getLayoutedElements = (
  nodes: Node[],
  edges: Edge[],
  direction: 'TB' | 'LR' = 'TB'
) => {
  const g = new dagre.graphlib.Graph();
  g.setGraph({ rankdir: direction });
  g.setDefaultEdgeLabel(() => ({}));

  nodes.forEach((node) => {
    g.setNode(node.id, { width: 172, height: 36 });
  });

  edges.forEach((edge) => {
    g.setEdge(edge.source, edge.target);
  });

  dagre.layout(g);

  const layoutedNodes = nodes.map((node) => {
    const pos = g.node(node.id);
    return {
      ...node,
      position: { x: pos.x - 86, y: pos.y - 18 }, // Center to top-left
    };
  });

  return { nodes: layoutedNodes, edges };
};

Core Concepts

Coordinate System Difference

Critical: Dagre returns center coordinates; React Flow uses top-left.

// Dagre output: center of node
const dagrePos = g.node(nodeId); // { x: 100, y: 50 } = center

// React Flow expects: top-left corner
const rfPosition = {
  x: dagrePos.x - nodeWidth / 2,
  y: dagrePos.y - nodeHeight / 2,
};

Node Dimensions

Dagre requires explicit dimensions. Three approaches:

1. Fixed dimensions (simplest):

g.setNode(node.id, { width: 172, height: 36 });

2. Per-node dimensions from data:

g.setNode(node.id, {
  width: node.data.width ?? 172,
  height: node.data.height ?? 36,
});

3. Measured dimensions (most accurate):

// After React Flow measures nodes
g.setNode(node.id, {
  width: node.measured?.width ?? 172,
  height: node.measured?.height ?? 36,
});

Layout Directions

| Value | Direction | Use Case | |-------|-----------|----------| | TB | Top to Bottom | Org charts, decision trees | | BT | Bottom to Top | Dependency graphs (deps at bottom) | | LR | Left to Right | Timelines, horizontal flows | | RL | Right to Left | RTL layouts |

g.setGraph({ rankdir: 'LR' }); // Horizontal layout

Hard gates

Run these in order before treating layout as correct (each step has an objective pass condition):

1. Dimensions match conversion — For every node id, the width and height given to g.setNode for that id are the same numbers used to compute position.x / position.y from g.node(id) (half-width / half-height must match the dagre node box).
2. Center → top-left — position is { x: centerX - width/2, y: centerY - height/2 }, not raw g.node(id).x / .y alone.
3. React Flow state update — After programmatic layout, setNodes / setEdges receive a new array instance (e.g. [...layouted] or layouted.map(...)), not the previous reference unchanged.
4. Optional sanity — If you use fitView after layout, it runs after nodes are committed (e.g. next requestAnimationFrame or setTimeout(0)), not in the same synchronous tick as setNodes with stale measurements.

Complete Implementation

Basic Layout Function

import dagre from '@dagrejs/dagre';
import type { Node, Edge } from '@xyflow/react';

interface LayoutOptions {
  direction?: 'TB' | 'BT' | 'LR' | 'RL';
  nodeWidth?: number;
  nodeHeight?: number;
  nodesep?: number;  // Horizontal spacing
  ranksep?: number;  // Vertical spacing (between ranks)
}

export function getLayoutedElements(
  nodes: Node[],
  edges: Edge[],
  options: LayoutOptions = {}
): { nodes: Node[]; edges: Edge[] } {
  const {
    direction = 'TB',
    nodeWidth = 172,
    nodeHeight = 36,
    nodesep = 50,
    ranksep = 50,
  } = options;

  const g = new dagre.graphlib.Graph();
  g.setGraph({ rankdir: direction, nodesep, ranksep });
  g.setDefaultEdgeLabel(() => ({}));

  nodes.forEach((node) => {
    const width = node.measured?.width ?? nodeWidth;
    const height = node.measured?.height ?? nodeHeight;
    g.setNode(node.id, { width, height });
  });

  edges.forEach((edge) => {
    g.setEdge(edge.source, edge.target);
  });

  dagre.layout(g);

  const layoutedNodes = nodes.map((node) => {
    const pos = g.node(node.id);
    const width = node.measured?.width ?? nodeWidth;
    const height = node.measured?.height ?? nodeHeight;

    return {
      ...node,
      position: {
        x: pos.x - width / 2,
        y: pos.y - height / 2,
      },
    };
  });

  return { nodes: layoutedNodes, edges };
}

React Flow Integration

import { useCallback } from 'react';
import {
  ReactFlow,
  useNodesState,
  useEdgesState,
  useReactFlow,
  ReactFlowProvider,
} from '@xyflow/react';
import { getLayoutedElements } from './layout';

const initialNodes = [
  { id: '1', data: { label: 'Start' }, position: { x: 0, y: 0 } },
  { id: '2', data: { label: 'Process' }, position: { x: 0, y: 0 } },
  { id: '3', data: { label: 'End' }, position: { x: 0, y: 0 } },
];

const initialEdges = [
  { id: 'e1-2', source: '1', target: '2' },
  { id: 'e2-3', source: '2', target: '3' },
];

// Apply initial layout
const { nodes: layoutedNodes, edges: layoutedEdges } = getLayoutedElements(
  initialNodes,
  initialEdges,
  { direction: 'TB' }
);

function Flow() {
  const [nodes, setNodes, onNodesChange] = useNodesState(layoutedNodes);
  const [edges, setEdges, onEdgesChange] = useEdgesState(layoutedEdges);
  const { fitView } = useReactFlow();

  const onLayout = useCallback((direction: 'TB' | 'LR') => {
    const { nodes: newNodes, edges: newEdges } = getLayoutedElements(
      nodes,
      edges,
      { direction }
    );

    setNodes([...newNodes]);
    setEdges([...newEdges]);

    // Fit view after layout with animation
    window.requestAnimationFrame(() => {
      fitView({ duration: 300 });
    });
  }, [nodes, edges, setNodes, setEdges, fitView]);

  return (
    <div style={{ width: '100%', height: '100vh' }}>
      <div style={{ position: 'absolute', zIndex: 10, padding: 10 }}>
        <button onClick={() => onLayout('TB')}>Vertical</button>
        <button onClick={() => onLayout('LR')}>Horizontal</button>
      </div>
      <ReactFlow
        nodes={nodes}
        edges={edges}
        onNodesChange={onNodesChange}
        onEdgesChange={onEdgesChange}
        fitView
      />
    </div>
  );
}

export default function App() {
  return (
    <ReactFlowProvider>
      <Flow />
    </ReactFlowProvider>
  );
}

useAutoLayout Hook

Reusable hook for automatic layout:

import { useCallback, useEffect, useRef } from 'react';
import {
  useReactFlow,
  useNodesInitialized,
  type Node,
  type Edge,
} from '@xyflow/react';
import dagre from '@dagrejs/dagre';

interface UseAutoLayoutOptions {
  direction?: 'TB' | 'BT' | 'LR' | 'RL';
  nodesep?: number;
  ranksep?: number;
}

export function useAutoLayout(options: UseAutoLayoutOptions = {}) {
  const { direction = 'TB', nodesep = 50, ranksep = 50 } = options;
  const { getNodes, getEdges, setNodes, fitView } = useReactFlow();
  const nodesInitialized = useNodesInitialized();
  const layoutApplied = useRef(false);

  const runLayout = useCallback(() => {
    const nodes = getNodes();
    const edges = getEdges();

    const g = new dagre.graphlib.Graph();
    g.setGraph({ rankdir: direction, nodesep, ranksep });
    g.setDefaultEdgeLabel(() => ({}));

    nodes.forEach((node) => {
      g.setNode(node.id, {
        width: node.measured?.width ?? 172,
        height: node.measured?.height ?? 36,
      });
    });

    edges.forEach((edge) => {
      g.setEdge(edge.source, edge.target);
    });

    dagre.layout(g);

    const layouted = nodes.map((node) => {
      const pos = g.node(node.id);
      const width = node.measured?.width ?? 172;
      const height = node.measured?.height ?? 36;

      return {
        ...node,
        position: { x: pos.x - width / 2,