ImplementingGameplayElementsUsingGamebryo
Chapter2:ControllingCharactersandViewingtheGameLevel2
AbouttheNiEntityFramework
We will create our character and third person camera components using the NiEntity
framework inthischapter. The NiEntity frameworkenables game scenes tobe loaded, saved,
andmanipulated.Now,if
youhavestudiedotherGamebryotutorials,andhavereadthereference
manual, then you may be thinking, “I can do the very same thing using standard Gamebryo
objectsand NIFfiles.Why shouldIconsider usingthe NiEntityframeworkinstead?” Thisisa
goodquestion!Thisframeworkwon’tbethebest
solutionforallgames,butitdoesofferacouple
ofcompellingfeaturesforourpurposes.
Reason number one: the Gamebryo Scene Designer application, a Gamebryo level design and
editing tool, creates scenes that are based on NiEntity. The NiEntity framework is able to
loadlevelsbuiltusingSceneDesigner
andsaved as*.gsa files.SinceSceneDesignerisaconvenient
waytobuild completegame levels,whendevelopingcomplex gamesit onlymakessensetotake
advantage ofit. (In Chapter1, we tookadvantage ofNiEntity to enableus toload scenesthat
had been designed using the
Gamebryo SceneDesigner application, and we used some limited
featuresofNiEntitytospawntheplayer’sselectedcharacterintothechosengamelevel.)
Reasonnumbertwo:theNiEntityframeworkisbasedontheideaofexposingobjectproperties
andfunctionalityviareflection.Thatis,theframeworkprovidesgenericfunctionsfordiscoverin g
andmanipulatingpropertiesofobjectsatruntimeratherthanatcompiletime.ThisenablesScene
Designertoprovidegenericeditingofproperties,andtoalloweditingofobjectsimplementedin
custom, game‐specific libraries that are not linked directly into the standard binary builds of
Scene Designer. In later chapters,
we will exploit this generic runtime access to properties and
functionality to integrate a scripting language. It will enable us to minimize the amount of
specializedcoderequiredtoexposefunctionalitytothescriptingengine.
AddingaComponenttotheNiEntityFrameworktoEnableCharacterAnimationControl
Thefirstthingwe
aregoingtodoisaddabitofcodethatwillenableustochangethelocomotion
state of the player’s character. Recall from Chapter 1 (source code reference) that the
m_pkPlayableCharacter member of the MainGamePlay state class was a pointer to the
entityrepresentingthecharacterthatthe
playerchosepriortostartingthegame.Wearegoingto
addplayercontrolofthischaracter.
A game scene, represented by an NiScene object, contains both the current game level being
played and any actors that are participating in the level. The m_pkPlayableCharacter
member variableisa pointer tothe
virtualinterface class, NiEntityInterface; however, the
concreteobjectthatthemembervariablepointstoisaNiGeneralEntityobjectthatcontains
anNiActorComponent.Thiscombination istheNiEntityframework’swayofrepresentingan
animatedcharacterinthescene.
TheNiActorComponentprovidesaccess(viaintrospection)tocharacter‐specificpropertiesand
features,
includingtheabilitytochangetheanimationstateofthecorrespondingcharacterandto
place and orient the character in the scene. The component ultimately makes use of the core
