### Hierarchy

- Layout
  - LayeredDigraphLayout

This arranges nodes of directed graphs into layers (rows or columns). There are many samples that use LayeredDigraphLayout.

If you want to experiment interactively with most of the properties, try the Layered Digraph Layout sample. See samples that make use of LayeredDigraphLayout in the samples index.

The layerSpacing property controls the distance between layers. The columnSpacing property controls the breadth of each "column" -- this affects the distance between nodes within a layer, although the exact distance also depends on the breadth of each node. The layeringOption property determines whether nodes without links coming in or without links going out are lined up at the edge of the graph, or whether they are positioned close to their connected nodes.

By default the layout will route the links in a manner that is consistent with the direction. So, for example, if the direction is 90 degrees (i.e. downward), the links are expected to go from the top towards the bottom. That means the links should come out from the bottom of the ports and should go into the top of the ports. Basically the layout will set Link.fromSpot to `Spot.Bottom` and Link.toSpot to `Spot.Top`.

If you want to the links to use the spots that are given by the ports or by the links themselves, you will need to set setsPortSpots to false to prevent this layout from setting the spots on the links. For example, if each node only has one port that is the whole node, and if you want the links to be spread out along the sides of the nodes, then you should set setsPortSpots to false and set the node's GraphObject.fromSpot to `Spot.BottomSide` and GraphObject.toSpot to `Spot.TopSide`.

This layout handles links that form cycles better than TreeLayout does. The normal routing behavior for "backwards" links is to route them "around" the source node and "around" the destination node, so that all links come in one side and go out the other side. However if you want "backwards" links to go more directly between nodes, set setsPortSpots to false and the node's GraphObject.fromSpot and GraphObject.toSpot both to `Spot.TopBottomSides`. (Of course if the direction is zero or 180, you'll want to use `Spot.LeftRightSides`.

If the diagram is structured in a tree-like fashion, it may be better to use TreeLayout, which has more options specific to trees. TreeLayout is much faster than LayeredDigraphLayout, and can handle a limited number of links that would prevent the graph structure from being a true tree (i.e. some nodes having multiple parents).

This layout makes use of a LayoutNetwork of LayeredDigraphVertexes and LayeredDigraphEdges that normally correspond to the Nodes and Links of the Diagram.

The layout algorithm consists of four-major steps: Cycle Removal, Layer Assignment, Crossing Reduction, and Straightening and Packing. The layout cannot guarantee that it provides optimal positioning of nodes or routing of links.

## Index

### Constructors

- constructor

### Properties

- aggressiveOption
- columnSpacing
- cycleRemoveOption
- direction
- initializeOption
- iterations
- layerSpacing
- layeringOption
- maxColumn
- maxIndex
- maxIndexLayer
- maxLayer
- minIndexLayer
- packOption
- setsPortSpots

### Methods

- assignLayers
- commitLayers
- commitLayout
- commitLinks
- commitNodes
- createNetwork
- doLayout

### Constants

- AggressiveLess
- AggressiveMore
- AggressiveNone
- CycleDepthFirst
- CycleFromLayers
- CycleGreedy
- InitDepthFirstIn
- InitDepthFirstOut
- InitNaive
- LayerLongestPathSink
- LayerLongestPathSource
- LayerOptimalLinkLength
- PackAll
- PackExpand
- PackMedian
- PackNone
- PackStraighten

## Constructors

### constructor

- new LayeredDigraphLayout(): LayeredDigraphLayout

- Constructs a LayeredDigraphLayout with no Layout.network and with no owning Layout.diagram.

  #### Returns LayeredDigraphLayout

## Properties

### aggressiveOption : EnumValue

- Gets or sets which aggressive option is being used to look for link crossings. The default value is LayeredDigraphLayout.AggressiveLess.

### columnSpacing : number

- Gets or sets the size of each column. This value must be positive and it defaults to 25.

### cycleRemoveOption : EnumValue

- Gets or set which cycle removal option is used. The default value is LayeredDigraphLayout.CycleDepthFirst.

### direction : number

- Gets or sets the direction the graph grows towards. 0 is towards the right, 90 is downwards, 180 is towards the left, and 270 is upwards. The default value is 0.

### initializeOption : EnumValue

- Gets or sets which indices initialization option is being used. The default value is LayeredDigraphLayout.InitDepthFirstOut.

### iterations : number

- Gets or sets the number of iterations to be done. The value must be non-negative. The default value is 4.

### layerSpacing : number

- Gets or sets the space between each layer. This value must be positive and it defaults to 25.

### layeringOption : EnumValue

- Gets or sets which layering option is being used. The default value is LayeredDigraphLayout.LayerOptimalLinkLength.

### Read-only maxColumn : number

- This read-only property returns the largest column value.

### Read-only maxIndex : number

- This read-only property returns the largest index value.

### Read-only maxIndexLayer : number

- This read-only property returns the larges index layer.

### Read-only maxLayer : number

- This read-only property returns the largest layer value.

### Read-only minIndexLayer : number

- This read-only property returns the smallest index layer.

### packOption : number

- Gets or sets the options used by the straighten and pack function, The default value is LayeredDigraphLayout.PackAll.

### setsPortSpots : boolean

- Gets or sets whether the FromSpot and ToSpot of each link should be set to values appropriate for the given value of LayeredDigraphLayout.direction. The default value is true.

  If you set this to false, the spot values of the links and port objects will be used. If you do not set the spot values to sensible values matching the direction, the routing results may be poor and they may cross over nodes.

## Methods

### Protected Virtual assignLayers

- assignLayers(): void

- Assigns every vertex in the input network to a layer. The layer is a non-negative integer describing which row of vertexes each vertex belongs in. (Do not confuse this concept of "layer" with Layers that control the Z-ordering of Parts.)

  The layering satisfies the following relationship: if L is a link from node U to node V, then U.layer > V.layer.

  This method can be overridden to customize how nodes are assigned layers. Please read the Introduction page on Extensions for how to override methods and how to call this base method. By default, this does the appropriate assignments given the value of layeringOption.

  since

    1.1

  #### Returns void

### Protected Virtual commitLayers

- commitLayers(layerRects: Array<Rect>, offset: Point): void

- This overridable method is called by commitLayout to support custom arrangement of bands or labels across each layout layer. By default this method does nothing.

  The coordinates used in the resulting Rects may need to be offset by the Layout.arrangementOrigin.

  since

    1.4

  #### Parameters

  - ##### layerRects: Array<Rect>

    an Array of Rects with the bounds of each of the "layers"

  - ##### offset: Point

    the position of the top-left corner of the banded area relative to the coordinates given by the layerRects

  #### Returns void

### Protected Override commitLayout

- commitLayout(): void

- Set the fromSpot and toSpot on each Link, position each Node according to the vertex position, and then position/route the Links.

  This calls the commitNodes and commitLinks methods, the latter only if isRouting is true. You should not call this method -- it is a "protected virtual" method. Please read the Introduction page on Extensions for how to override methods and how to call this base method.

  #### Returns void

### Protected Virtual commitLinks

- commitLinks(): void

- Routes the links.

  This is called by commitLayout. This is only called if Layout.isRouting is true. See also commitNodes. Please read the Introduction page on Extensions for how to override methods and how to call this base method.

  #### Returns void

### Protected Virtual commitNodes

- commitNodes(): void

- Commit the position of all nodes.

  This is called by commitLayout. See also commitLinks. Please read the Introduction page on Extensions for how to override methods and how to call this base method.

  #### Returns void

### Override createNetwork

- createNetwork(): LayeredDigraphNetwork

- Create a new LayoutNetwork of LayeredDigraphVertexes and LayeredDigraphEdges.

  #### Returns LayeredDigraphNetwork

  a new LayoutNetwork.

### Override doLayout

- doLayout(coll: Diagram | Group | Iterable<Part>): void

- Perform the layered digraph layout.

  If there is no Layout.network, this calls makeNetwork to create a LayoutNetwork from the given collection of Parts. This removes any reflexive edges in the network, since they should be ignored.

  In order to influence a vertex's layer, you can override assignLayers.

  Finally this calls Layout.updateParts to commit the Node positions from the vertex positions. Layout.updateParts calls commitLayout within a transaction.

  #### Parameters

  - ##### coll: Diagram | Group | Iterable<Part>

    A Diagram or a Group or a collection of Parts.

  #### Returns void

## Constants

### Static AggressiveLess : EnumValue

The faster, less aggressive, crossing reduction algorithm; a valid value for LayeredDigraphLayout.aggressiveOption.

### Static AggressiveMore : EnumValue

The slower, more aggressive, crossing reduction algorithm, a valid value for LayeredDigraphLayout.aggressiveOption.

### Static AggressiveNone : EnumValue

The fastest, but poorest, crossing reduction algorithm; a valid value for LayeredDigraphLayout.aggressiveOption.

### Static CycleDepthFirst : EnumValue

Remove cycles using depth first cycle removal; a valid value of LayeredDigraphLayout.cycleRemoveOption.

### Static CycleFromLayers : EnumValue

Remove cycles depending on assignLayers determining entirely which links are backwards links; a valid value of LayeredDigraphLayout.cycleRemoveOption.

### Static CycleGreedy : EnumValue

Remove cycles using greedy cycle removal; a valid value of LayeredDigraphLayout.cycleRemoveOption.

### Static InitDepthFirstIn : EnumValue

Initialize using depth first in initialization; a valid value for LayeredDigraphLayout.initializeOption.

### Static InitDepthFirstOut : EnumValue

Initialize using depth first out initialization; a valid value for LayeredDigraphLayout.initializeOption.

### Static InitNaive : EnumValue

Initialize using naive initialization; a valid value for LayeredDigraphLayout.initializeOption.

### Static LayerLongestPathSink : EnumValue

Assign layers using longest path sink layering; a valid value for LayeredDigraphLayout.layeringOption.

### Static LayerLongestPathSource : EnumValue

Assign layers using longest path source layering; a valid value for LayeredDigraphLayout.layeringOption.

### Static LayerOptimalLinkLength : EnumValue

Assign layers using optimal link length layering; A valid value for LayeredDigraphLayout.layeringOption.

### Static PackAll : number

Enable all options for the LayeredDigraphLayout.packOption property; See also LayeredDigraphLayout.PackExpand, LayeredDigraphLayout.PackStraighten, and LayeredDigraphLayout.PackMedian.

### Static PackExpand : number

This option gives more chances for the packing algorithm to improve the network, but is very expensive in time for large networks; a valid value for LayeredDigraphLayout.packOption.

### Static PackMedian : number

This option tries to have the packing algorithm center groups of nodes based on their relationships with nodes in other layers, a valid value for LayeredDigraphLayout.packOption.

### Static PackNone : number

Does minimal work in packing the nodes; a valid value for LayeredDigraphLayout.packOption.

### Static PackStraighten : number

This option tries to have the packing algorithm straighten many of the links that cross layers, a valid value for LayeredDigraphLayout.packOption.

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