GUI Scripting Language

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

IMPORTANT: THIS PAGE & SERIES IS A WORK IN PROGRESS

Introduction

Inherited from Doom 3, TDM has a specialized GUI 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.

Customizing Aspects of Your FM 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.

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.

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

If-Clauses

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-Clauses

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, 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.

Names and Scope [REVISE THIS FURTHER]

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"
  }
} REVISE THIS FURTHER

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

Good to Know

Examples [REVISE DESCRIPTIONS]

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.

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.) Details about each type can be found in their Properties descriptions.

Used throughout the core main menu hierarchy:

  • editDef - text input, e.g., the name of a game save file, and for specifying certain video options.
  • choiceDef – widely used for making choices among settings.
  • sliderDef – widely used as a horizontal slider to control a setting value.
  • listDef – provides a scrollable multi-column list control. Examples include mission downloads, mission select, and saved game select.

Rarely used:

  • bindDef – used just In the Controls submenu, to bind particular keys to particular functions.
  • 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.

Details

Additional Event Handler Commands

Arcana

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