For those of you whom are using this excellent opensource diagram software, since OS X Yosemite it seems it lacks one line to work correctly.
You must edit : ‘/Applications/Dia.app/Contents/Ressources/bin/dia’ and add at line 39 : “export DISPLAY=:O” such as :
[…]
fi
fi
export DISPLAY=:0
osascript -e ‘tell app “XQuartz” to launch’
for i in `seq 1 30`; do
[…]
Now it must work correctly 🙂