NForceDirectedLayout Class

In This Topic

The NForceDirectedLayout class is a graph layout, which layouts the graph vertices and edges, according to the forces acting on them. It serves as base class for all types of force directed layouts.

Object Model

Syntax

Visual Basic
C#

'Declaration
 
<System.ComponentModel.TypeConverterAttribute(System.ComponentModel.ExpandableObjectConverter)>
Public MustInherit Class NForceDirectedLayout 
   Inherits NGraphLayout
   Implements Nevron.Diagram.INMeasurements, Nevron.Diagram.INMeasurementUnit, Nevron.Diagram.INResolution, Nevron.Dom.INAttribute, Nevron.Dom.INHistoryCallback, Nevron.INReferenceHolder, Nevron.INReferenceProvider

'Usage
 
Dim instance As NForceDirectedLayout

[System.ComponentModel.TypeConverter(System.ComponentModel.ExpandableObjectConverter)]
public abstract class NForceDirectedLayout : NGraphLayout, Nevron.Diagram.INMeasurements, Nevron.Diagram.INMeasurementUnit, Nevron.Diagram.INResolution, Nevron.Dom.INAttribute, Nevron.Dom.INHistoryCallback, Nevron.INReferenceHolder, Nevron.INReferenceProvider

Remarks

The force directed layout basically implements an iterative algorithm, which tries to minimize the physical energy (reach equilibrium), enduced by the forces in the provided graph. Different force directed layouts use different sets of forces, however all forces are derived from the base NForce class.

In general the algorithm performs the following steps:

fixed vertices are such vertices, which cannot be moved in both X and Y directions. Their initial placement is controlled by an instance of the NFixedVertexPlacement class, accessible from the FixedVertexPlacement property.
free vertices are such vertices, which can be moved in X or Y directions. Their initial placement is controlled by an instance of the NFreeVertexPlacement class, accessible from the FreeVertexPlacement property.
the iteration phase is repeated until all enabled forces are activated. At each iteration phase the algorithm tries to reach equilibrium in the number of iterations specified by the MaxIterations property. At each iteration the algorithm first accumulates the forces acting on all vertices and then ask the enviroment to apply them (actually move the vertices). The enviroment is represented by an instance of the NForceEnvironment class, accessible from the ForceEnvironment property.

The force directed layout provides the following optional force model:

The magnetic field force tries to impose an orientation of the edges in the graph. It is represented by an instance of the NMagneticFieldForce class, accessible from the MagneticFieldForce property.
The bounce back force forces tries to additionally repel overlapping vertices. It is represented by an instance of the NBounceBackForce class, accessible from the BounceBackForce property.
The gravity force forces tries to attact the vertices to the current barycenter of the graph. It is represented by an instance of the NGravityForce class, accessible from the GravityForce property.

All of the above mentioned forces are by default disabled and their activation pass is set to 1. In this way, if any of those forces is enabled, the graph will be given a chance to relax during the first pass, in which only the primary force model will act.

Inheritance Hierarchy

System.Object
   Nevron.Dom.NAttribute
      Nevron.Diagram.Layout.NLayout
         Nevron.Diagram.Layout.NGraphPartsLayout
            Nevron.Diagram.Layout.NGraphLayout
               Nevron.Diagram.Layout.NForceDirectedLayout
                  Nevron.Diagram.Layout.NBarycenterLayout
                  Nevron.Diagram.Layout.NSpringLayout
                  Nevron.Diagram.Layout.NSymmetricalLayout

Requirements

Target Platforms: Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

Reference

NForceDirectedLayout Members
Nevron.Diagram.Layout Namespace

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