Skip to content

Advanced Custom Code

For experienced developers who want complete control over how the GMC behaves, there are advanced options for hooking into, extending, and overriding all GMC behavior.

Extending Core Script Classes

Each of the core scripts of GMC (outlined here) has a registered class name that allows the script to be extended or overridden. Many of these classes have virtual methods for code paths that would be common use cases, and any method on the class can be extended or overridden.

Create a Custom Core Script

To insert your own code into the core GMC scripts, create a new GDScript file that extends from the core script class you want.

You can then create your own logic for virtual methods, extend existing methods with super(), or overwrite them entirely.

    # /custom_code/

    extends GMCServer

    # Override a virtual method
    func on_connect():
      print("Connection established, running custom startup flow.")

    # Extend an existing method by calling super() and adding custom logic
    func set_machine_var(name: String, value) -> void:
      print("Machine var %s updated to value: %s" % [name, value])

Inject Custom Script into GMC

Now that your script is written, you can instruct GMC to use your script instead of the core script by configuring it in gmc.cfg.

In your gmc.cfg file, create a new section named [gmc] and enter a key of the class name you're overriding and a value of the path to your custom script.


The available core scripts to override are:

  1. GMCUtil - Utility functions for common scenarios
  2. GMCLogger - Logging handler for MPF-style logging
  3. GMCGame - Game data from MPF (player and machine vars, modes, settings)
  4. GMCServer - The BCP server (sending, receiving, and processing events)
  5. GMCMedia - The media controller for slides, widgets, and sounds

Note that the core scripts are loaded in the above order and earlier scripts cannot reference later ones.

Something missing or wrong? You can fix it!

This website is edited by people like you! Is something wrong or missing? Is something out of date, or can you explain it better?

Please help us! You can fix it yourself and be an official "open source" contributor!

It's easy! See our Beginner's guide to editing the docs.

Page navigation via the keyboard: < >

You can navigate this site via the keyboard. There are two modes:

General navigation, when search is not focused:

  • F , S , / : open search dialog
  • P , , : go to previous page
  • N , . : go to next page

While using the search function:

  • Down , Up : select next / previous result
  • Esc , Tab : close search
  • Enter : go to highlighted page in the results