I wanted to make a pie chart script that counts lines of code.
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It's currently not possible with PlantUML, but you may use Google charts or other web service to add charts:
Example:
@startuml start :foo; note left You can use images <img:https://chart.googleapis.com/chart?cht=p3&chd=t:60,40&chs=250x100&chl=Hello|World> end note stop @enduml
Graphviz has the wedged style that can be applied to nodes, and look like a pie chart, so maybe this could be used to draw a pie chart.