PlantUML allows you to use several different layout engines.
The following 4 apply to most diagrams.
See these 4 variants of a SAREF4CITY diagram for comparison
(this is an RDF graph using the Smart Applications REFerence Ontology (SAREF) extension for Smart Cities).
The source is example1-saref4city.puml and is generated from a Turtle file).
The notes below are based on observing only these examples, so they are subjective.
- Graphviz is the default engine. Relies on an external program
- Smetana. Use
!pragma layout smetana in the file or -Playout=smetana on the command-line. A port of Graphviz to Java. Tends to make slightly straighter arrows
- VizJs uses JavaScript. Use
-graphvizdot vizjs on the command line. Tends to space out nodes more, resulting in a bigger diagram.
- ELK (Eclipse Layout Kernel). Use
!pragma layout elk in the file or -Playout=elk on the command-line. Supports only orthogonal layout, and doesn't cover all features
Sequence diagrams have 2 engines:
- "puma" is the older and still default engine
- teoz is a new engine that has some unique features: anchors (named arrows/messages), duration, nested boxes. More features are in development (see teoz in the forum), eg parallel messages
ditaa (Ascii Art) diagrams have an optional engine:
- noditaa replaces
ditaa with java code. It's a beta release from 2019 that hasn't been updated
A number of options affect aspects of the layout. We list them below with links to forum threads:
- #4418, #3111, #4045
!pragma svek_trace: saves dot and svg files for debugging
- #1343
!pragma aspect: aspect ratio. May be obsolete, since aspect is not found on the graphviz attrs page, and attrs-test is missing altogether.
- #1226
!pragma ratio: aspect ratio. Currently seems broken: specifying two numbers m,n causes graphviz error.
- #977
skinparam nodesep: space between nodes in pixels.
- #977
skinparam ranksep: space between node ranks.
- #1608
skinparam linetype ortho: orthogonal layout (but label position is wrong, see plantuml/backlog#11)
- #1608
skinparam linetype polyline: straight not curved edges
- #4387 #5007
together: keep nodes next to each other
- #3188
norank: edge doesn't count for the layout process
- #8365
hidden: invisible edge that counts for the layout process
- #4418, #1132, #3231, #3111, #3143
!pragma horizontalLineBetweenDifferentPackageAllowed: allow to make a horizontal line between packages. (Also see #1628 on layout of grouping components)
- #1296
skinparam minClassWidth: make nodes not narrower than this
- #1296
skinparam sameClassWidth: make all nodes the same width
- #4637
skinparam minClassWidth on sequence diagrams
- #2538
layout__new__line for disconnected parts of a diagram
- #3118
skinparam padding and margin for title, footer, etc
- #5493
skinparam ParticipantPadding and skinparam BoxPadding: padding on sequence diagrams
Achieving good layout with PlantUML is sometimes non-trivial.
See PlantUML GraphViz Layout by Mark George at University of Otago
for more advice.
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