/dagre-react-flow

name: dagre-react-flow
description: Automatic graph layout using dagre with React Flow (@xyflow/react). Use when implementing auto-layout, hierarchical layouts, tree structures, or arranging nodes programmatically. Triggers on dagre, auto-layout, automatic layout, getLayoutedElements, rankdir, hierarchical graph.

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 } = getLay