Context of the Smetana project
PlantUML uses link::graphviz-dot[Graphviz/DOT] to compute node positionning for some UML diagrams (only link::use-case-diagram[usecase diagrams], link::class-diagram[class diagrams], link::object-diagram[object diagrams], link::component-diagram[component diagrams], link::deployment-diagram[deployment diagram], link::state-diagram[state diagrams] and link::activity-diagram-legacy[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 :
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PlantUML has to create a new process for each diagram, (and communication with this new process could be source of bugs).
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Users have to install link::graphviz-dot[DOT] on their system, in addition of Java.
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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
@endumlThe key point is that this image has been generated without launching Graphviz/DOT!
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=smetana
[Ref. issue-582]