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agtools / Tutorial 4 - Introducing Entities



You can build the STE example with:

> ./
> make clean; make

This will build 7 programs (tutor4a-tutor4g.prg) which should execute consecutively from the auto folder.

You can build the STF version of tutor4g with:

> ./
> make clean; make stf

This will build 1 program (stf.prg) which should execute from the auto folder.

This tutorial will introduce Entities and demonstrate how much can be done using them with very little code.

The Entity system is the most important and useful part of AGT, because it provides a way to populate the game world with objects which have a life of their own, and which can interact with and respond to other objects.

Our Entity tutorial continues here:

Individual Tutorials:

Tutorial 4a: From Sprites to Entities

Tutorial 4b: The Thinking Entity

Tutorial 4c: Independent Entities

Tutorial 4d: Entities in Local Coordinates #1

Tutorial 4e: Entities in Local Coordinates #2

Tutorial 4f: Smarter Entities

Tutorial 4g: Finishing Touches


Entities can be summarised as follows:

Each entity is of a specific type. A type might represent a spaceship, a rock or a player character. The types are user-defined. There is no practical limit to the number of types which can be defined. Each project can define its own types. The types are each given a unique number.

Each entity type has default characteristics which are specified in a global dictionary. These default characteristics are copied into every instance spawned of that type.

An entity type can be instanced multiple times in the same game world. This is called spawning. For example you may define an entity of type TREE and then instance 30 TREEs at various places on the game map. The default characteristics for TREE are copied into every TREE instance.

Every entity instance has its own state - it's own potentially unique characteristics. For example two TREEs will typically have different world coordinates. Two animated FIRE entities will likely have separate animation frames showing at any time. Two instances with complex AI behaviour will occupy different thinking states at different times.

Entities have an optional 'thinking' or tick function. This allows each instance to reason about its own state, and to an extent, the state of significant others. A tick function can modify nearly everything about an entity instance, including its own tick function.

Entities have an optional interaction or collide function. This allows each instance to respond to others touching it, if they are capable of doing so. The collide function can edit the state of the affected entity or the entity which affected it.

Last, entities have a draw method which can be one of several builtin methods, a custom method, or nothing (invisible). The draw method can be changed at any time. To accommodate drawing, an asset may be attached which provides the material to be drawn.