In PlantUML v1.2026.3 - v1.2026.8, specifying a minimum width for sequence diagram participant boxes causes the internal text to align left instead of being centered. Explicit layout alignments like HorizontalAlignment center are ignored.
Steps to Reproduce:
The issue occurs whenever the participant box size is expanded programmatically using either <style> or skinparam:
@startuml
<style>
sequenceDiagram {
participant {
' This causes the text inside the participant box to align LEFT
MinimumWidth 100
HorizontalAlignment center
}
}
</style>
' Note: The same bug occurs when using legacy skinparam in recent versions:
' skinparam MinClassWidth 100
participant "A" as A
participant "LongNameParticipant" as B
A -> B : Message
@enduml
If the text length is shorter than the defined minimum width (e.g., participant "A"), the text is strictly locked to the left edge of the box.
Additional Context
• In v1.2025.10, setting the minimum width via skinparam (e.g., skinparam { sequence { Participant { MinimumWidth 100 } } } or MinClassWidth) successfully maintained text centering.
• In v1.2026.2, setting the minimum width via style (e.g., <style> sequenceDiagram { participant { MinimumWidth 100 } } </style> or MinClassWidth) successfully maintained text centering.
