QuakeC Field Types

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Revision as of 15:12, 8 May 2008 by ShoTro (talk | contribs) (New page: <h2>The field types</h2> <h4>What's a field?</h4> <p>Countrary to the other types, the entity type is a reference to an instance of a structured object, that contains many informations ...)
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The field types

What's a field?

Countrary to the other types, the entity type is a reference to an instance of a structured object, that contains many informations of totally different kinds.

To access all these informations conveniently, they are stored as fields of the entity object, and each field is given a name and a type, that makes it distinct of the others.

Some of the fields do not store value, but instead they store the function to be executed in certain conditions. They are called the methods that can be aplied to the object.

If Quake-C was an object oriented programming language, those method functions and would be distinguished from the other fields. And, above all, you would be able to create new object types, with their own fields.

As Quake-C stands currently, all the field definitions are definitions of entity fields. So anywhere in your code you could add definition of new fields, and the compiler would interpret them as an extension of the entity definition.

Creating new fields

The only way to extend the entity type is to add some fields at the end of the structures.

This is done via a field definitions, whose general structure is:

   .type field_name;

For instance, if you wanted to add a sling to the game, and needed to store the count of pellets for every player, you would add the following line in the source code:

   .float ammo_sling;

That will add a fields ammo_sling to every entity in the game, and in particular to the player entities.

Here are all the possible definitions of entity fields, with their types:

    .float field_name;
    .string field_name;
    .vector field_name;
    .entity field_name;

The strange bit is that you can add those type definitions almost anywhere in the source code. They are not supposed to be grouped in a single place, where the entity type would be defined.

Allowed modifications of types

In the first file read by the Quake-C compiler, defs.qc, there must be a definition for the entity fields, and world fields. This definition is hard coded. You had better not touch it, or you will have to recompile Quake itself.

The globals are defined before the special definition void end_sys_globals;
The entity fields are defined before the special definition void end_sys_fields;

It's not important if you don't understand the nonsense above. It's an ugly hack. Just don't modify defs.qc before those two tags, and you won't be in trouble.