fsm - How can I implement dialog trees into my game?

What is the best way to implement a dialog tree system in my game? I want an NPC to give the player different sets of responses, some which may only appear when the Player has an item or a previous event has occurred.

Answer

Dialog Trees should be done using XML. You store the conditions for the responses and the response in nested trees with a reference to a script file if you need to do something more complex.

You should keep the scripts and dialog separate especially if you are putting together an RPG which has a metric ton worth of conversations. You can then use a library like simpleXML to read the XML file.

There's a similar question over on SO with an example: https://stackoverflow.com/questions/372915/game-logic-in-xml-files