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:
@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
@endumlThis diagram is generated using ELK.
You can use the -P link::command-line[command-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 link::class-diagram[class diagram] and link::deployment-diagram[deployment diagram] and tell us what you think about the result.