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Chapter 29. Analysis and Specification

Key Topics

Objects in the World
Behavior Enhancements
Specification

At this stage of the book, the reactive animats are competent enough to perform various tasks such as wandering around and engaging basic combat. To make them more intelligent , we must increase their capabilities by allowing them to perform short sequences of actions (such as using doors or platforms and dodging incoming fire). Although these short plans are still short- term reactive behaviors, they can make the animats appear surprisingly realistic.

The next few pages prepare the development of these behaviors by analyzing the platform, understanding the problem, and specifying the world interfaces. This process is relatively familiar now, with the previous parts covering it in depth, so progression through these phases is much quicker here.

This chapter covers the following topics:

The objects in the game environment, both items that can be picked up and contraptions that affect the movement. How they affect the player and how they are dealt with by the engine.
The way human players manage to develop behaviors to use items and contraptions. A case study of each individual behavior for later use during the application phase.
A specification that extends many of the existing interfaces described throughout this book.

At the end of this chapter, we'll have a code skeleton ready for an implementation of these behaviors.

Objects in the World

The game environment is scattered with many different objects, most of which have a purpose. The design of first-person shooters includes items such as health packs , armor , and silencers to enhance the experience. Contraptions such as ladders, platforms, and doors also diversify the gameplay.

Items

Some items in the game have a direct effect on the player's state. When picked up, health packs and stimpacks increase the player's health immediately. The same applies to the various forms of armor; the combat armor, the jacket and vest, as well as the shards contribute positively to the player's armor count. Although Quake 2 has some subtleties with different armor types (for instance, conversions between green, yellow, and red), the general pattern is very similar to most first-person shooters; the player automatically benefits from health and armor and does not need to pay attention to it.

On the other hand, some items are not always used directly -such as quad damage (four times weapon strength), health regeneration, invincibility, and the silencer. In single-player modes, these items are stored in the inventory, and only activated when the player uses them. During multiplayer games , such as deathmatch or capture the flag, these items are activated automatically in Quake 2 . This speeds up the game, requires strategy to maximize the benefits of object collection, and increases the importance of item placement.

Contraptions

Because the worlds in first-person shooters are quite realistic, players often encounter challenges such as doors, ladders, and elevators. In many cases, these contraptions have particular structural design goals, such as slowing down escape from a key area or preventing easy access to important weapons.

Specific sequences of actions are often required to activate these contraptions, as defined by the game logic. For example, pressing a switch calls the platform, a key unlocks a door, and the player needs to touch the ladder face on before climbing it. These actions are prerequisites for any player in the world to use these objects.

A Test Bed

Because health and armor are essential parts of deathmatch games, most levels are designed with many items scattered around. We'll have no trouble finding the levels with such items, or testing the AI's capabilities at collecting these items.

On the other hand, contraptions such as doors, teleporters, ladders, platforms, or even jump pads are relatively rare. When they are present, these elements are usually centerpieces to the architecture of a level. Developing the artificial intelligence (AI) requires a variety of different levels as a test bed, because a unique level with all the required features will be hard to find. Developing the AI for ladders and platforms proves somewhat challenging regardless. Indeed, contraptions are quite rare, so there won't be too many opportunities for the animat to test its behaviors.

Using customized simplified levels is a common practice applicable in this case, but precautions are necessary to guarantee that the AI is capable of generalizing to real game levels. To increase the likelihood of encountering training situations, the animat can be taught in phases by alternating complementary behaviors -for example, going up a ladder and down again. This will provide ample opportunities to develop the necessary skills in the animats, although this approach depends on a separate training period. (Running back and forth can't be done during the game.)