GUI Scripting Language

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Overview and hub of the "GUI Scripting" series by Geep, 2022



Inherited from Doom 3, TDM has a specialized GUI ("Graphical User Interface") layout language within .gui text files to define:

  • Full-screen dialogs, such as menus
  • Screen overlays, such as popup messages, HUD items and underwater murk.
  • Active game-world surfaces like readables or custom video effects.

This language differs from that of .script files. It describes the visual appearance and (to some extent) behavior – including text display - of nested rectangular areas. For mappers, these areas can be manipulated through .script files. Beyond that, for menu developers interfacing to C++ code, it allows defining what MS Windows traditionally called "dialog controls", for selection from lists or multiple choices, setting values from sliders, and entry of text.

The Basics for Mappers

Need I Learn GUI Scripting?

Often not! For the mapper, much can be accomplished without much GUI wrangling.

FM Customizing Using Only #defines in a Standard GUI

The TDM main menu hierarchy is set up to allow you to customize it without really knowing GUI scripting, just by commenting/uncommenting particular #defines. Such customizations include:

  • Main menu background art or music
  • Aspects of pre-mission briefing (text or video)
  • Aspects of post-mission debriefing (text or video)

You do this by overriding the core "guis/mainmenu_custom_defs.gui" file with your own altered copy. See the comments in that file for details.

Deploying Stock GUIs or the Entities that Use Them

For many things you want to do, there’s already a provided gui-using entity and/or stock or sample .gui files. For particular guidance, see:

Tools & Tricks for GUI Scripting

Occasionally, you may need to craft a .gui from scratch, or as a novel customization. You can do this in a text editor, but be aware that the .gui language is quirky, and the existing parsing system unhelpful in detecting errors.

Because GUI scripts are in separate files (with the .gui extension), they can be developed independently from the rest of the game code. A change in a GUI does not require a DMAP (unless an associated entity changes). Furthermore, GUI scripts can be reloaded on real time, which makes for easy debugging and testing.

A Basic "windowDef" Template

With nomenclature used in this series.

Every .gui file (unless designed just to be #included) must have a top-level "windowDef" structure, typically named "Desktop". Nested within, there may be more windowDefs (and other members of the "guiDef" family described further below), each with a locally-unique <name>. The basic template outline, with the terminology used in this series, is:

windowDef <Name> {
<Property List>
<User Variable List>

<Nested Child windowDefs or other guiDefs>

<Event Handlers>

Nesting of child guiDefs can be as deep as you need.

Property List

This is zero or more "Properies", by convention each on its own line. A Property has a predefined name, type (Boolean, float, vec2, vec4, string) and default value. If a property is not listed, it still exists, with its default value.

User Variable List

This is zero or more "User Variables", by convention each on its own line. Unlike Properties, a User Variable is not predefined. This is a float typically used as a bool. It always has a default value of 0.

Event Handlers

An "Event Handler" catches user actions, .script requests, or elapsed time occurrences, and has general syntax:

<onHandler> [handler_param] {
  <If-Clauses> and <GUI Script Commands>

The two most widely used event handlers are:

  • onTime time - fires when time in milliseconds is reached, for the specific guiDef’s timer.
  • onNamedEvent event - Catches a custom event, generated by your entity’s script function (e.g., in a script object). Or catches an engine-generated event. See GUI Scripting: Named Events.

For a full list, with syntax and usage examples, see GUI Scripting: Event Handlers.

If Statements

Within the body of an Event Handler, if-clauses read or compare properties and user variables, then alter program flow accordingly. Basic syntax is:

  • if (condition) {...} else if (another_condition) {...} else {...}

For details, see GUI Scripting: If Statements

GUI Script Commands

In the body of an Event Handler, including within arms of if-clauses, GUI script commands read and change properties, user variables, GUI: parameters, and timer functions. Most widely used are:

  • set variable value_or_source;
  • transition property start_value end_value time_duration [accel decel];
  • resetTime time;

For a full list, with syntax and usage examples, see GUI Scripting: Commands.


Unlike some other languages, properties and user variables in a parent guiDef are not immediately visible to a child. Instead, the parent's name must be included as a prefix followed by "::" (two colons):

windowDef Desktop {
  visible 1
  windowDef Child1 {
      visible "Desktop::visible"

Also, there are GUI:: Parameters, that can be shared among guiDefs and .scripts. See:

Good to Know

GUI:: Parameters



Preprocessor Directives


More Advanced Topics

Developers working on improvements to TDM core systems - the main menus, briefings, HUD, or entities with active surfaces - must be conversant with additional aspects of GUI scripting. Mappers too will want to understand such aspects if they are developing analogous but novel visual items.

Main Menu Tool Tips

Near the bottom of a guiDef for the main menu system, you may see something like:


See GUI Scripting:Tooltip Macro for more.

Other "GuiDef" Types

The term "guiDef" has been coined here to describe the main layout structure shown in the template above, but generalized beyond just windowDef. (Other tutorial authors use "Window", "Item", or "Def" for this; see GUI Scripting: TDM vs Doom 3, Quake 4.)

Follow the links below for details about each type, including their additional Properties.

Used throughout the core main menu hierarchy:


See GUI Scripting: EditDef - text input, e.g., the name of a game save file, and for specifying certain video options.


See GUI Scripting: ChoiceDef – widely used for making choices among settings.


See GUI Scripting: SliderDef – widely used as a horizontal slider to control a setting value.


See GUI Scripting: ListDef – provides a scrollable multi-column list control. Examples include mission downloads, mission select, and saved game select.

Rarely used:


See GUI Scripting: BindDef – used just In the Controls submenu, to bind particular keys to particular functions.


See GUI Scripting: RenderDef – used to show a 3D model in an guiDef, typically an overlay. This is not a static snapshot or sprite, but an object that could be oriented, e.g., by code. In the game HUD, used for the compass playertool.

Additional Event Handler Commands

Set 'Cmd'

For a way for a main-menu GUi to invoke C++ engine functions, see GUI Scripting: Parsing of Set 'Cmd'.

Fetching CVars

See GUI Scripting: Getting System CVars.


Formal Syntax Definition

See GUI Scripting: BNF.

TDM vs Doom 3 or Quake 4

For usage and nomenclature differences, see GUI Scripting: TDM vs Doom 3, Quake 4.

References and Resources

For sources used in this series, including other early GUI scripting tutorials, see GUI Scripting: References & Resources.

The idTech4 Built-in EditGuis Editor

See GUI Scripting: EditGuis Editor