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Context of the Smetana project
PlantUML uses Graphviz/DOT to compute node positionning for some UML diagrams (only usecase diagrams, class diagrams, object diagrams, component diagrams, deployment diagram, state diagrams and Legacy activity diagrams). The fact that DOT computes automatically the position of node is a key feature, and algorithms implemented in DOT usually give very good result.

However, there are some drawbacks of using DOT : the computation is done by an external program (dot.exe on Windows, dot on linux), and that means that :

  • PlantUML has to create a new process for each diagram, (and communication with this new process could be source of bugs).
  • Users have to install DOT on their system, in addition of Java.
  • PlantUML is not fully portable.

Another way of using DOT would be to use it as a library, and to link it with PlantUML using JNI (Java Native Interface) but that would not be perfect thought.

If a Java version of Graphviz/DOT would exist, this would allow to greatly simplify the installation and the use of PlantUML. So we have started a port from C to Java of GraphViz/DOT source code: see Smetana project

Using Smetana

Smetana code has been integrated into PlantUML, so you can use the !pragma layout smetana directive to force PlantUML to use Smetana (the internal Java port of GraphViz/Dot embedded in PlantUML sources) instead of the regular dot process. 

@startuml
!pragma layout smetana
class Foo1

Foo1 --> Foo2
Foo1 --> Foo3
Foo1 ---> Foo4 : test 4
Foo1 ----> Foo5 : test 5

@enduml

The key point is that this image has been generated without launching Graphviz/DOT!

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

java -jar plantuml.jar -Playout=smetana

[Ref. issue-582]

Alternative layout engines

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

Please report any bugs to plantuml@gmail.com or here.
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