dagre

What is dagre?

The dagre npm package is a JavaScript library that provides facilities for graph layout. It is particularly useful for arranging nodes and edges in a directed graph, ensuring that the layout is visually appealing and easy to understand. Dagre uses a combination of algorithms to position nodes and edges in a way that minimizes edge crossings and distributes nodes evenly.

What are dagre's main functionalities?

Graph Creation

This feature allows you to create a new graph, add nodes, and define edges between them. The code sample demonstrates how to initialize a graph, set default properties, and add nodes and edges.

const dagre = require('dagre');
const g = new dagre.graphlib.Graph();
g.setGraph({});
g.setDefaultEdgeLabel(() => ({}));
g.setNode('a', { label: 'Node A', width: 50, height: 50 });
g.setNode('b', { label: 'Node B', width: 50, height: 50 });
g.setEdge('a', 'b');

Graph Layout

This feature performs the layout of the graph, positioning the nodes and edges in a visually appealing manner. The code sample shows how to apply the layout algorithm to the graph and retrieve the computed positions of the nodes.

const dagre = require('dagre');
const g = new dagre.graphlib.Graph();
g.setGraph({});
g.setDefaultEdgeLabel(() => ({}));
g.setNode('a', { label: 'Node A', width: 50, height: 50 });
g.setNode('b', { label: 'Node B', width: 50, height: 50 });
g.setEdge('a', 'b');
dagre.layout(g);
console.log(g.node('a')); // { label: 'Node A', width: 50, height: 50, x: 50, y: 50 }
console.log(g.node('b')); // { label: 'Node B', width: 50, height: 50, x: 150, y: 50 }

Other packages similar to dagre

cytoscape

Cytoscape is a graph theory library for visualizing and analyzing network data. It provides a wide range of layout algorithms and is highly customizable. Compared to dagre, Cytoscape offers more advanced features for interactive graph visualization and analysis.

d3-force

d3-force is a module of the D3.js library that provides force-directed graph layout algorithms. It is highly flexible and can be used to create dynamic, interactive visualizations. While dagre focuses on directed graphs, d3-force is more general-purpose and can handle various types of graph layouts.

elkjs

ELK (Eclipse Layout Kernel) is a layout engine for graph visualization. The elkjs package is a JavaScript port of ELK. It offers a variety of layout algorithms and is known for its high-quality layouts. Compared to dagre, ELK provides more options and fine-tuning capabilities for complex graph layouts.

README

dagre - Graph layout for JavaScript

Dagre is a JavaScript library that makes it easy to lay out directed graphs on the client-side.

Key priorities for this library are:

1. Completely client-side computed layout. There are great, feature-rich alternatives, like graphviz, if client-side layout is not a requirement for you.

2. Speed. Dagre must be able to draw medium sized graphs quickly, potentially at the cost of not being able to adopt more optimal or exact algorithms.

3. Rendering agnostic. Dagre requires only very basic information to lay out graphs, such as the dimensions of nodes. You're free to render the graph using whatever technology you prefer. We use D3 in some of our examples and highly recommend it if you plan to render using CSS and SVG.

Note that dagre is current a pre-1.0.0 library. We will do our best to maintain backwards compatibility for patch level increases (e.g. 0.0.1 to 0.0.2) but make no claim to backwards compatibility across minor releases (e.g. 0.0.1 to 0.1.0). Watch our CHANGELOG for details on changes.

Getting Dagre

Browser Scrips

You can get the latest browser-ready scripts:

• dagre.js
• dagre.min.js

NPM Install

Before installing this library you need to install the npm package manager.

To get dagre from npm, use:

$ npm install dagre

Build From Source

Before building this library you need to install the npm package manager.

Check out this project and run this command from the root of the project:

$ make dist

This will generate dagre.js and dagre.min.js in the dist directory of the project.

Using Dagre

A Note on Rendering

As mentioned above, dagre's focus in on graph layout only. This means that you need something to actually render the graphs with the layout information from dagre.

There are a couple of options for rendering:

• dagre-d3 is a D3-based renderer for dagre.
• JointJS is a renderer that provides facilities for editing a graph after it has been rendered.

An Example Layout

First we need to load the dagre library. In an HTML page you do this by adding the following snippet:

<script src="http://PATH/TO/dagre.min.js"></script>

In node.js you use:

var dagre = require("dagre");

We use graphlib to create graphs in dagre, so its probably worth taking a look at its API. Graphlib comes bundled with dagre. In this section, we'll show you how to create a simple graph.

A node must be an object with the following properties:

• width - how wide the node should be in pixels
• height - how tall the node should be in pixels

The attributes would typically come from a rendering engine that has already determined the space needed for a node.

Here's a quick example of how to set up nodes and edges:

// Create a new directed graph
var g = new dagre.Digraph();

// Add nodes to the graph. The first argument is the node id. The second is
// metadata about the node. In this case we're going to add labels to each of
// our nodes.
g.addNode("kspacey",    { label: "Kevin Spacey",  width: 144, height: 100 });
g.addNode("swilliams",  { label: "Saul Williams", width: 160, height: 100 });
g.addNode("bpitt",      { label: "Brad Pitt",     width: 108, height: 100 });
g.addNode("hford",      { label: "Harrison Ford", width: 168, height: 100 });
g.addNode("lwilson",    { label: "Luke Wilson",   width: 144, height: 100 });
g.addNode("kbacon",     { label: "Kevin Bacon",   width: 121, height: 100 });

// Add edges to the graph. The first argument is the edge id. Here we use null
// to indicate that an arbitrary edge id can be assigned automatically. The
// second argument is the source of the edge. The third argument is the target
// of the edge.
g.addEdge(null, "kspacey",   "swilliams");
g.addEdge(null, "swilliams", "kbacon");
g.addEdge(null, "bpitt",     "kbacon");
g.addEdge(null, "hford",     "lwilson");
g.addEdge(null, "lwilson",   "kbacon");

Next we can ask dagre to do the layout for these nodes and edges. This is done with the following code:

var layout = dagre.layout().run(g);

An object with layout information will be attached to each node and edge under the dagre property.

The node's dagre object has the following properties:

• x - the x-coordinate of the center of the node
• y - the y-coordinate of the center of the node

The edge's dagre object has a points property, which is an array of objects with the following properties:

• x - the x-coordinate for the center of this bend in the edge
• y - the y-coordinate for the center of this bend in the edge

For example, the following layout information is generated for the above objects:

layout.eachNode(function(u, value) {
    console.log("Node " + u + ": " + JSON.stringify(value));
});
layout.eachEdge(function(e, u, v, value) {
    console.log("Edge " + u + " -> " + v + ": " + JSON.stringify(value));
});

Prints:

Node kspacey: {"id":"kspacey","width":144,"height":100,"rank":0,"order":0,"ul":0,"ur":0,"dl":0,"dr":0,"x":84,"y":50}
Node swilliams: {"id":"swilliams","width":168,"height":100,"rank":2,"order":0,"ul":0,"ur":0,"dl":0,"dr":0,"x":84,"y":180}
Node bpitt: {"id":"bpitt","width":108,"height":100,"rank":2,"order":1,"ul":188,"ur":188,"dl":188,"dr":188,"x":272,"y":180}
Node hford: {"id":"hford","width":168,"height":100,"rank":0,"order":1,"ul":364,"ur":364,"dl":364,"dr":364,"x":448,"y":50}
Node lwilson: {"id":"lwilson","width":144,"height":100,"rank":2,"order":2,"ul":364,"ur":364,"dl":364,"dr":364,"x":448,"y":180}
Node kbacon: {"id":"kbacon","width":121,"height":100,"rank":4,"order":0,"ul":188,"ur":188,"dl":0,"dr":364,"x":272,"y":310}

Edge kspacey -> swilliams: {"points":[{"x":84,"y":115,"ul":0,"ur":0,"dl":0,"dr":0}],"id":"_E0","minLen":2,"width":0,"height":0}
Edge swilliams -> kbacon: {"points":[{"x":84,"y":245,"ul":0,"ur":0,"dl":0,"dr":0}],"id":"_E1","minLen":2,"width":0,"height":0}
Edge bpitt -> kbacon: {"points":[{"x":272,"y":245,"ul":188,"ur":188,"dl":188,"dr":188}],"id":"_E2","minLen":2,"width":0,"height":0}
Edge hford -> lwilson: {"points":[{"x":448,"y":115,"ul":364,"ur":364,"dl":364,"dr":364}],"id":"_E3","minLen":2,"width":0,"height":0}
Edge lwilson -> kbacon: {"points":[{"x":448,"y":245,"ul":364,"ur":364,"dl":364,"dr":364}],"id":"_E4","minLen":2,"width":0,"height":0}

Besides just the x and y coordinates there are other debug attributes that are not guaranteed to be present.

Configuring the Layout

Here are a few methods you can call on the layout object to change layout behavior:

• debugLevel(x) sets the level of logging verbosity to the number x. Currently 4 is th max.
• nodeSep(x) sets the separation between adjacent nodes in the same rank to x pixels.
• edgeSep(x) sets the separation between adjacent edges in the same rank to x pixels.
• rankSep(x) sets the sepration between ranks in the layout to x pixels.
• rankDir(x) sets the direction of the layout.
  • Defaults to "TB" for top-to-bottom layout
  • "LR" sets layout to left-to-right

For example, to set node separation to 20 pixels and the rank direction to left-to-right:

var layout = dagre.layout()
                  .nodeSep(20)
                  .rankDir("LR")
                  .run(g);

Input Graph

The input graph supplied for layout can have the following attributes:

Object	Attribute	Default	Description
graph	rankDir	TB	Direction for rank nodes. Can be TB, BT, LR, or RL, where T = top, B = bottom, L = left, and R = right.
node	height		The height of the node.
node	width		The width of the node.
edge	minLen	1	The number of ranks to keep between the source and target of the edge.

Output Graph

The output graph has the following attributes:

Object	Attribute	Description
graph	height	The height of the entire graph.
graph	width	The width of the entire graph.
node	x	The x-coordinate for the center of the node.
node	y	The y-coordinate for the center of the node.
edge	points	An array of { x, y } pairs for the control points of the edge.

Resources

• Issue tracker
• Mailing list

Recommend Reading

This work was produced by taking advantage of many papers and books. If you're interested in how dagre works internally here are some of the most important papers to read.

The general skeleton for Dagre comes from Gansner, et al., "A Technique for Drawing Directed Graphs", which gives both an excellent high level overview of the phases involved in layered drawing as well as diving into the details and problems of each of the phases. Besides the basic skeleton, we specifically used the technique described in the paper to produce an acyclic graph, and we use the idea of a minimum spanning tree for ranking. We do not currently use the network simplex algorithm for ranking. If there is one paper to start with when learning about layered graph drawing, this seems to be it!

For crossing minimization we used Jünger and Mutzel, "2-Layer Straightline Crossing Minimization", which provides a comparison of the performance of various heuristics and exact algorithms for crossing minimization.

For counting the number of edge crossings between two layers we use the O(|E| log |V_small|) algorithm described in Barth, et al., "Simple and Efficient Bilayer Cross Counting".

For positioning (or coordinate assignment), we derived our algorithm from Brandes and Köpf, "Fast and Simple Horizontal Coordinate Assignment". We made some some adjustments to get tighter graphs when node and edges sizes vary greatly.

Third Party Examples

Dagre has been included as a part of some very cool projects. Here are just a few that stand out:

JointJS has a plugin that uses dagre for layout. JointJS focuses on rendering and interaction with diagrams, which synergizes well with Dagre. If you want the ability to move nodes and manipulate edges interactively, this is a good place to start!

Jonathan Mace has a demo that makes it possible to interactively explore graphs. In his demo, you can highlight paths, collapse subgraphs, via detailed node information, and more!

nomnoml is a tool for drawing UML diagrams in a browser. It uses a custom renderer with dagre to draw the diagrams in an HTML5 canvas.

License

dagre is licensed under the terms of the MIT License. See the LICENSE file for details.