Force directed graph drawing layout
npm install ngraph.forcelayout.v2ngraph.forcelayout
==========================
This is a force directed
graph layouter in 2d. It is using quad tree as an n-body solver. This repository
is part of ngraph family, and operates on
ngraph.graph data structure. If you
want to go the 3D space, please check out ngraph.forcelayout3d
js
// graph is an instance of ngraph.graph object.
var layout = require('ngraph.forcelayout')(graph);
for (var i = 0; i < ITERATIONS_COUNT; ++i) {
layout.step();
}
// now we can ask layout where each node/link is best positioned:
graph.forEachNode(function(node) {
console.log(layout.getNodePosition(node.id));
// Node position is pair of x,y coordinates:
// {x: ... , y: ... }
});
graph.forEachLink(function(link) {
console.log(layout.getLinkPosition(link.id));
// link position is a pair of two positions:
// {
// from: {x: ..., y: ...},
// to: {x: ..., y: ...}
// }
});
`
Result of getNodePosition()/getLinkPosition() will be always the same for
the same node. This is true:
` js
layout.getNodePosition(1) === layout.getNodePosition(1);
`
Reason for this is performance. If you are interested in storing positions
somewhere else, you can do it and they still will be updated after each force
directed layout iteration.
"Pin" node and initial position
Sometimes it's desirable to tell layout algorithm not to move certain nodes.
This can be done with pinNode() method:
` js
var nodeToPin = graph.getNode(nodeId);
layout.pinNode(nodeToPin, true); // now layout will not move this node
`
If you want to check whether node is pinned or not you can use isNodePinned()
method. Here is an example how to toggle node pinning, without knowing it's
original state:
` js
var node = graph.getNode(nodeId);
layout.pinNode(node, !layout.isNodePinned(node)); // toggle it
`
What if you still want to move your node according to some external factor (e.g.
you have initial positions, or user drags pinned node)? To do this, call
setNodePosition() method:
` js
layout.setNodePosition(nodeId, x, y);
`
Monitoring changes
Like many other algorithms in ngraph family, force layout monitors graph changes
via graph events.
It keeps layout up to date whenever graph changes:
` js
var graph = require('ngraph.graph')(); // empty graph
var layout = require('ngraph.layout')(graph); // layout of empty graph
graph.addLink(1, 2); // create node 1 and 2, and make link between them
layout.getNodePosition(1); // returns position.
`
If you want to stop monitoring graph events, call dispose() method:
` js
layout.dispose();
`
Configuring physics
Since this is force directed layout, sometimes it's desirable to adjust physics simulator.
Please refer to ngraph.physics.simulator
to see source code and simulator parameters. Once you have instance of physics
simulator you can pass it as a second argument to layout constructor:
` js
// Configure
var physicsSettings = {
springLength: 30,
springCoeff: 0.0008,
gravity: -1.2,
theta: 0.8,
dragCoeff: 0.02,
timeStep: 20
};
// pass it as second argument to layout:
var layout = require('ngraph.forcelayout')(graph, physicsSettings);
`
You can get current physics simulator from layout by checking layout.simulator
property. This is a read only property.
Space occupied by graph
Finally, it's often desirable to know how much space does our graph occupy. To
quickly get bounding box use getGraphRect() method:
` js
var rect = layout.getGraphRect();
// rect.x1, rect.y1 - top left coordinates of bounding box
// rect.x2, rect.y2 - bottom right coordinates of bounding box
`
install
With npm do:
`
npm install ngraph.forcelayout
``