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 - Directed graph rendering

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.

Demo

Try our interactive demo!

Or see an example of rendering the TCP state diagram.

These demos and more can be found in the demo folder of the project. Simply open them in your browser - there is no need to start a web server.

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 graphlib from npm, use:

$ npm install graphlib

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

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.

For a simple starting point, we suggest looking at the user contributed demo/dagre-d3-simple.js script for doing good but easy rendering. To get started look at demo/sentence-tokenization.html.

Another option is to use JointJS. See the link for an article about how to use it with Dagre. The ability to manipulate nodes and edges after they are layed out and renderer can be very useful!

For even more control over rendering you can write a custom renderer or take advantage or a library like D3, which makes it easier to creates graphs with SVG. The code in demo/dagre-d3-simple.js uses D3, so this may be a good place to start.

Ultimately we plan to make available some basic renderers for Dagre in the near future.

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");

The current version of Dagre takes an array of nodes and edges, along with some optional configuration, and attaches layout information to the nodes and edges in the dagre property.

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.

An edge must be an object with either references to its adjacent nodes:

• source - a reference to the source node
• target - a reference to the target node

Or with the ids of its adjacent nodes:

• sourceId - the id of the source node
• targetId - the id of the target node

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

var nodes = [
    { id: "kspacey",   label: "Kevin Spacey",  width: 144, height: 100 },
    { id: "swilliams", label: "Saul Williams", width: 168, height: 100 },
    { id: "bpitt",     label: "Brad Pitt",     width: 108, height: 100 },
    { id: "hford",     label: "Harrison Ford", width: 168, height: 100 },
    { id: "oplat",     label: "Oliver Platt",  width: 144, height: 100 },
    { id: "kbacon",    label: "Kevin Bacon",   width: 121, height: 100 },

];
var edges = [
    { sourceId: "kspacey",   targetId: "swilliams" },
    { sourceId: "swilliams", targetId: "kbacon" },
    { sourceId: "bpitt",     targetId: "kbacon" },
    { sourceId: "hford",     targetId: "oplat" },
    { sourceId: "oplat",     targetId: "kbacon" }
];

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

dagre.layout()
     .nodes(nodes)
     .edges(edges)
     .run();

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:

nodes.forEach(function(u) {
    console.log("Node " + u.dagre.id + ": " + JSON.stringify(u.dagre));
});
edges.forEach(function(e) {
    console.log("Edge " + e.sourceId + " -> " + e.targetId + ": " +
                JSON.stringify(e.dagre));
});

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 oplat: {"id":"oplat","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 -> oplat: {"points":[{"x":448,"y":115,"ul":364,"ur":364,"dl":364,"dr":364}],"id":"_E3","minLen":2,"width":0,"height":0}
Edge oplat -> 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:

dagre.layout()
     .nodes(nodes)
     .edges(edges)
     .nodeSep(20)
     .rankDir("LR")
     .run();

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 couple 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!

License

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