Eclipse Layout Kernel

https://eclipse.dev/elk/
Admin
Eclipse Layout Kernel (ELK) is an infrastructure for connecting diagram editors to automatic layout...
Tokens:92,891
Snippets:1,136
Trust Score:10
Update:2 weeks ago
Show doc for...
Tokens:
Raw
### Start Hugo Server for ELK Documentation

Source: https://eclipse.dev/elk/documentation/contributors/buildingelk.html

Starts a Hugo server instance in the repository's docs/ folder for editing the ELK documentation website. The browser at http://localhost:1313/elk/ dynamically updates as files are edited and saved.

```bash
hugo server

```

--------------------------------

### Configure layout options with LayoutConfigurator

Source: https://eclipse.dev/elk/documentation/tooldevelopers/usingeclipselayout/advancedconfiguration.html

Shows how to create a LayoutConfigurator and set layout options on a specific graph object and on all nodes. The example sets INTERACTIVE and PORT_CONSTRAINTS on a specific node, and ALGORITHM and SPACING_NODE on all nodes.

```Java
LayoutConfigurator configurator = new LayoutConfigurator();

// Configure layout options for a concrete graph object
configurator.configure(myVerySpecialNode)
    .setProperty(CoreOptions.INTERACTIVE, true)
    .setProperty(CoreOptions.PORT_CONSTRAINTS, PortConstraints.FIXED);

// Configure layout options for all nodes
configurator.configure(KNode.class)
    .setProperty(CoreOptions.ALGORITHM, "org.eclipse.elk.layered")
    .setProperty(CoreOptions.SPACING_NODE, 30.0f);

```

--------------------------------

### ILayoutSetup interface methods

Source: https://eclipse.dev/elk/documentation/tooldevelopers/usingeclipselayout/connectingtoelk.html

Defines the two methods that an ILayoutSetup implementation must provide. The supports method is called by the diagram layout engine to determine if the setup can extract an ElkGraph from a given object, and createInjector returns a Guice injector that supplies the components needed for layout.

```java
boolean supports(Object object);
Injector createInjector(Module defaultModule);
```

--------------------------------

### Alternative Configuration with before and add

Source: https://eclipse.dev/elk/documentation/algorithmdevelopers/algorithmimplementation/algorithmstructure.html

Provides a marginally easier way to add multiple processors to the same slot using the before() and add() methods instead of repeated addBefore calls.

```java
private static final LayoutProcessorConfiguration<LayoutPhases, ElkNode> INTERMEDIATE_PROCESSING_CONFIG =
        LayoutProcessorConfiguration.<LayoutPhases, ElkNode>create()
            .before(LayoutPhases.P2_NODE_ORDERING)
                .add(IntermediateProcessorStrategy.ROOT_PROC)
                .add(IntermediateProcessorStrategy.FAN_PROC);
```

--------------------------------

### Disable symmetrical space reservation with ASYMMETRICAL

Source: https://eclipse.dev/elk/blog/posts/2025/25-08-22-node-labels.html

This example shows how to disable the symmetrical space reservation by setting nodeSize.options to ASYMMETRICAL.

```elk
node childWithLabelTopLeftAsymmetric {
    nodeLabels.placement: "INSIDE H_LEFT V_TOP"
    nodeSize.options: ASYMMETRICAL
    nodeSize.constraints: "NODE_LABELS"
    label "childWithLabelTopLeftAsymmetric"
    label "childWithLabelTopLeftAsymmetric2"
}

```

--------------------------------

### Combining Configurations with addAll

Source: https://eclipse.dev/elk/documentation/algorithmdevelopers/algorithmimplementation/algorithmstructure.html

Shows how to assemble different configurations based on graph features. It creates a base configuration from INTERMEDIATE_PROCESSING_CONFIG and conditionally adds additional processors using addAll.

```java
private static final LayoutProcessorConfiguration<LayoutPhases, ElkNode> FOO_PROCESSING_ADDITIONS =
        LayoutProcessorConfiguration.<LayoutPhases, ElkNode>create()
            .addBefore(LayoutPhases.P3_NODE_PLACEMENT, IntermediateProcessorStrategy.LEVEL_HEIGHT)
            .addBefore(LayoutPhases.P4_EDGE_ROUTING, IntermediateProcessorStrategy.NODE_POSITION_PROC);

public LayoutProcessorConfiguration<LayoutPhases, ElkNode> getLayoutProcessorConfiguration(ElkNode graph) {
    // Basic configuration
    LayoutProcessorConfiguration<LayoutPhases, ElkNode> configuration =
            LayoutProcessorConfiguration.<LayoutPhases, ElkNode>createFrom(
                    INTERMEDIATE_PROCESSING_CONFIG);

    // Additional dependencies
    if (foo) {
        configuration.addAll(FOO_PROCESSING_ADDITIONS);
    }

    return configuration;
}
```

--------------------------------

### Build ELK Documentation Website with Hugo

Source: https://eclipse.dev/elk/documentation/contributors/buildingelk.html

Builds the ELK documentation website with Hugo. Run this command in the repository's docs/ folder.

```bash
hugo

```

--------------------------------

### Label object example

Source: https://eclipse.dev/elk/documentation/tooldevelopers/graphdatastructure/jsonformat.html

Labels can contain text. Layout algorithms generally don't perform size estimation, so specify a reasonable width and height.

```json
{
  text: "A magnificent text"
}
```

--------------------------------

### Basic LayoutProcessorConfiguration with addBefore

Source: https://eclipse.dev/elk/documentation/algorithmdevelopers/algorithmimplementation/algorithmstructure.html

Shows a simple implementation of getLayoutProcessorConfiguration that returns a static configuration specifying that ROOT_PROC and FAN_PROC are added before phase 2 (P2_NODE_ORDERING).

```java
private static final LayoutProcessorConfiguration<LayoutPhases, ElkNode> INTERMEDIATE_PROCESSING_CONFIG =
        LayoutProcessorConfiguration.<LayoutPhases, ElkNode>create()
            .addBefore(LayoutPhases.P2_NODE_ORDERING, IntermediateProcessorStrategy.ROOT_PROC)
            .addBefore(LayoutPhases.P2_NODE_ORDERING, IntermediateProcessorStrategy.FAN_PROC);

@Override
public LayoutProcessorConfiguration<LayoutPhases, ElkNode> getLayoutProcessorConfiguration(ElkNode graph) {
    return INTERMEDIATE_PROCESSING_CONFIG;
}
```

--------------------------------

### Symmetrical space reservation for node labels

Source: https://eclipse.dev/elk/blog/posts/2025/25-08-22-node-labels.html

This example shows the symmetrical space reservation for node labels when they are not centered. The node reserves space on the opposite side of the label to be symmetrical.

```elk
node childWithLabelTopLeft {
    nodeLabels.placement: "INSIDE H_LEFT V_TOP"
    nodeSize.constraints: "NODE_LABELS"
    label "childWithLabelTopLeft"
    label "childWithLabelTopLeft2"
}

```

--------------------------------

### Extended edge example

Source: https://eclipse.dev/elk/documentation/tooldevelopers/graphdatastructure/jsonformat.html

Extended edges have mandatory sources and targets arrays, can be hyperedges, and may specify edge sections for layout. Many layout algorithms don't support hyperedges.

```json
{
  sources*: [ ..array of node and / or port identifiers.. ],
  targets*: [ ..array of node and / or port identifiers.. ],
  sections: [ ..array of edge sections.. ],
  labels: [ ..array of label objects.. ]
}
```

--------------------------------

### Primitive edge example

Source: https://eclipse.dev/elk/documentation/tooldevelopers/graphdatastructure/jsonformat.html

Primitive edges have a source and target node and can optionally connect to source and target ports. They are supported for legacy models; exported graphs use extended edges.

```json
{
  source*: node identifier,
  sourcePort: port identifier,
  target*: node identifier,
  targetPort: port identifier,
  sourcePoint: {x, y},
  targetPoint: {x, y},
  bendPoints: [ .. {x, y} pairs .. ],
  labels: [ ..array of label objects.. ]
}
```

--------------------------------

### Simple layout algorithm metadata file

Source: https://eclipse.dev/elk/documentation/algorithmdevelopers/metadatalanguage.html

Defines a bundle, an option 'reverseInput', and an algorithm 'simple' that supports several ELK properties with overridden defaults. The algorithm uses SimpleLayoutProvider and SimpleOptions metadata class.

```elkt
package cds.layout.simple

import cds.layout.simple.SimpleLayoutProvider
import org.eclipse.elk.core.math.ElkPadding

bundle {
    metadataClass options.SimpleMetaDataProvider
    idPrefix cds.layout.simple
}

option reverseInput : boolean {
    label "Reverse Input"
    description
        "True if nodes should be placed in reverse order of their
        appearance in the graph."
    default = false
    targets parents
}

algorithm simple(SimpleLayoutProvider) {
    label "Simple Layout Algorithm"
    description
        "This layout provider places nodes along a horizontal or a vertical line."
    metadataClass options.SimpleOptions

    supports reverseInput
    supports org.eclipse.elk.padding = new ElkPadding(10)
    supports org.eclipse.elk.spacing.edgeEdge = 5
    supports org.eclipse.elk.spacing.edgeNode = 10
    supports org.eclipse.elk.spacing.nodeNode = 10
}

```

--------------------------------

### Small Example JSON Graph

Source: https://eclipse.dev/elk/documentation/tooldevelopers/graphdatastructure/jsonformat.html

Minimal JSON graph with a root node, two children, and one edge. Uses the layout option "elk.direction": "RIGHT" to set the layout direction.

```json
{
  id: "root",
  layoutOptions: { "elk.direction": "RIGHT" },
  children: [
    { id: "n1", width: 10, height: 10 },
    { id: "n2", width: 10, height: 10 }
  ],
  edges: [{
    id: "e1", sources: [ "n1" ], targets: [ "n2" ]
  }]
}

```
Tokens:
Raw