# Generating state machines with Dia

Dia is a nice cross platform application for diagram drawing. It can be scripted via Python, which opens the possibility to generate code from Dia diagrams.

Below we’ll create a python plugin that generates C code from UML state machine diagrams. Doing the same for other languages should be trivial.

The first thing you need is Unai Estébanez Sevilla’s nice finite state machine code generator. The version that we are using here has been abstracted in order to be able to produce code in various languages.

This python plugin implements an exporter to C code. To use it, you need to put it, along with the base exporter into your local plugins directory under ~/.dia/python.

Let’s have a quick look at the code.

First we import the dia python module and the exporter base functionality:

import dia
import uml_stm_export


Then we create our C exporter class that inherits from the generic exporter:

class CDiagramRenderer(uml_stm_export.SimpleSTM):


Next we define how the beginning of our generated code file should look like. That could include general infrastructure independent of the state machine diagram at hand. In our case, we want to encapsulate the generated state machine code within a function:

CODE_PREAMBLE="void config_stm(STM_t* stm) {"


We also define the postamble to close the function. After that come generic functions that implement the class constructor init(self) and functions responsible for calling the dia object parser begin_render(self,data,filename).

Now we define our output generator end_render(self). We first traverse dia’s objects in order to find the state machine’s initial state:

for transition in self.transitions:
if(transition.source == "INITIAL_STATE"):


The initial state state gets a special treatment: we have a special function call generated for it:

f.write("    add_initial_state( stm, %s, %s );\n" %
(initial_state.name, initial_state.doaction))


Next we traverse all states and output code that will create them, along with functions to be called within that state to decide on where to transition next:

for key in self.states.keys():
f.write("    add_state( stm, %s, %s );\n"
% (state.name, state.doaction))


And finally we output all the transitions between states:

for transition in self.transitions:
f.write("    add_transition( stm, %s, %s, %s );\n" %
(transition.source, transition.trigger, transition.target))


and that’s nearly it. At the end of our generator we make sure to register it with dia:

dia.register_export("State Machine Cstma Dump", "c", CDiagramRenderer())


Done! Simple, isn’t it?

Finally please permit me to thank all the people that created such a powerful tool free for us to use:

• Unai Estébanez Sevilla for the original STM generator
• Steffen Macke and Hans Breuer, Dia’s current busy maintaners
• Alexander Larsson, Dia’s original author
• all the other contributors to Dia and free software
• Panter for inviting me to their fabulous work week in Greece where most of the hacking on the generator was done and Combitool who supported this work by needing a state machine generator in their current project.

PS: Unai’s original text generator is now also “just” a “simple” addon