Eclipse Layout Kernel

PlantUML uses an external layout engine for some diagrams (classes, use cases...). By default, GraphViz/dot is used. This means that PlantUML has to call an external process to generate some diagrams.

There are some work in progress to change this behavior. For example, a port of GraphViz to Java is ongoing.

Recently, Hallvard Trætteberg teaches us on how to use Eclipse Layout Kernel as a library to process the layout.

This is still alpha-software, but results are very interesting. This is working starting from V1.2021.5.

Usage

ELK is distributed as an independent library. So you have to build it yourself, or you can download the complete jar file here.

Both plantuml.jar and elk-full.jar have to be in the very same folder. You cannot rename elk-full.jar

Once installed, you can invoke ELK instead of GraphViz with the !pragma layout elk directive.

Example:

🎉 Copied!
@startuml
!pragma layout elk

package image {
	package color {
		class red
		class green
		
		red->green : red to green
	}
	package size {
		class big
		class small
	}
	class image1
	class image2
	image1 <|-- image2 
	
	size -> color : link between packages
}

class foo
class bar

foo -> bar : foo to bar
image1 "1" -> "*" bar
@enduml

This diagram is generated using ELK.

You can use the -Pcommand-line option to specify the pragma, rather than putting it in the puml file:

java -jar plantuml.jar -Playout=elk

[Ref. issue-582]

Do not expect too much right now, this is really an alpha-version. The idea is to get feedback from users, to know if we should continue in this direction (that is, supporting ELK within PlantUML).

Still, you can test class diagram and deployment diagram and tell us what you think about the result.

See smetana and vizjs for other alternatives to graphviz-dot.