Introduction to the Unreal Development Kit

Introduction to the Unreal
Development Kit (UDK)
Nick Prühs
October 23, 2013

About Me
“Best Bachelor“ Computer Science
Kiel University, 2009
Master Games
Hamburg University of Applied Sciences, 2011
Lead Programmer
Daedalic Entertainment, 2011-2012

Co-Founder
slash games, 2013

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Features
• complete editing environment
• pure rendering power (Gemini)
• state-of-the-art animation
(Mantinee)

• powerful scripting (Kismet)
• real worlds physics
• eye-popping lighting and shadows (Lightmass)

Features (Cont.)
• gorgeous cinematics (Mantinee)
• terrain
• built-in networking
• real-time shaders
• broad audio support
• particle effects (Cascade)

Features (Cont.)
• artificial intelligence
• distributed computing (Swarm)
• descructible environments
• Bink video codec
• SpeedTree foliage editor
• FaceFX facial animation
• Scaleform 4.0 UI

Licensing
• non-commercial use:
• free!

• commercial use:
• USD 99 up-front
• 0% royalty on first USD 50,000 in UDK related revenue
• 25% royalty on UDK related revenue above USD 50,000

Useful Stuff
• UT Source Code
• UDK Forums
• Showcases
• UDK Programming Home
• UDK Gems
• UnrealScript Language Reference

Working With The UDK
• UDK vs. Licensees
• monthly releases
• Feb 12: Recast
• May 12: RealD 3D
• Feb 13: Substance

• Visual Studio 2010 & nFringe
• UnrealEd & UnrealFrontend
• Content Packages

Unreal Engine Basics
• Core
• C++
• Rendering, Sound, GameLoop, Collision, Physics,
Threading, Low Level Network

• Virtual Machine
• runs in core
• executes UnrealScript

Unreal Engine Basics (Cont.)
• UnrealScript
• similar to C++ and Java
• high-level object-oriented language
• pointerless environment with automatic garbage
collection
• simple single-inheritance class graph
• strong compile-time type checking
• safe client-side execution "sandbox"

UnrealScript Features
• instantiation
• Actor.Spawn(class<Actor>) vs. new

• timers
• Actor.SetTimer(float, bool, name)

• iterators
• Actor.AllActors
• Actor.DynamicActors
• Actor.CollidingActors

UnrealScript Features (Cont.)
• states
state Dead
{
ignores SeePlayer, HearNoise, KilledBy, NextWeapon, PrevWeapon;
function bool IsDead()
{
return true;
}
// ...
}

Source: PlayerController.uc

• exec functions
.Bindings=(Name="MouseScrollDown",Command="GBA_NextWeapon")

Source: DefaultInput.ini

• exec functions
.Bindings=(Name="MouseScrollDown",Command="GBA_NextWeapon")

Source: DefaultInput.ini
exec function NextWeapon()
{
if ( WorldInfo.Pauser!=None )
return;
if ( Pawn.Weapon == None )
{
SwitchToBestWeapon();
return;
}
if ( Pawn.InvManager != None )
Pawn.InvManager.NextWeapon();
}

Source: PlayerController.uc

• config files
class HWPawn extends HWSelectable
config(HostileWorldsUnitData)
abstract;
/** The value the damage of all attacks is reduces by before being applied. */
var config int Armor;
/** The ground movement speed of this unit, in UU/s. */
var config int MovementSpeed;

Source: HWPawn.uc

• config files
class HWPawn extends HWSelectable
config(HostileWorldsUnitData)
abstract;
/** The value the damage of all attacks is reduces by before being applied. */
var config int Armor;
/** The ground movement speed of this unit, in UU/s. */
var config int MovementSpeed;

Source: HWPawn.uc
[HostileWorlds.HWSM_Commander]
Armor=0
MovementSpeed=160

Source: UDKHostileWorldsUnitData.ini

• localization files
class HWAbility extends Actor
config(HostileWorldsAbilityData)
abstract;
/** The name of this ability. */
var localized string AbilityName;

Source: HWAbility.uc

• localization files
class HWAbility extends Actor
config(HostileWorldsAbilityData)
abstract;
/** The name of this ability. */
var localized string AbilityName;

Source: HWAbility.uc
[HWAb_Cloak]
AbilityName=Cloak

Source: HostileWorlds.int

• meta data
/** Enable or disable spawning. */
Var() bool bEnableSpawning;
/** Set the rate at which AIs are spawned. */
Var() float RespawnsPerSecond<EditCondition=bEnableSpawning>;

Source: http://udn.epicgames.com/Three/UnrealScriptMetadata.html

Navigation Meshes
• connected graph of convex polygons
• at each node we know that an AI can get from any
point in that node, to any other point in that node
due to its convexity
• thus the task of pathfinding through the graph
simplifies into pathfinding along a connected graph
of nodes
• much more natural looking movement

Navigation Meshes (Cont.)

Source: http://udn.epicgames.com/Three/NavigationMeshReference.html

Obstacle Meshes
• represent obstacles in the world
• allow low-fidelity raycasts (against this obstacle
mesh only) when an AI needs to know whether it
can walk from one point to another directly
• allows us to skip doing a path search in wide open
areas even if there are many polygons between the
start and the goal

Benefits of Navigation Meshes
• can represent a large area with a single polygon
• overall graph density goes down
• memory footprint reduced
• pathfinding time goes down
• less time fixing up cross-level pathing information

• better pathing behavior
• automatic generation

Benefits of Navigation Meshes (Cont.)
• handling of dynamic objects

Source: http://udn.epicgames.com/Three/NavigationMeshReference.html

Weapons & Inventory
/** Holds the list of link guns linked to this weapon */

var array<UTWeap_LinkGun> LinkedList;

Source: UTWeap_LinkGun.uc

// I made a funny Hahahahah :)

Network
“Unreal views the general problem of coordinating a
reasonable approximation of a shared reality
between the server and clients as a problem of
replication.
That is, a problem of determining a set of data and
commands that flow between the client and server
in order to achieve that approximate shared reality.“

- Tim Sweeney, Epic Games Inc.

Network
• generalized client-server model
• authoritative server (dedicated, listen)
• predicting and simulating clients
• “hybrid” code
• client and server execute same code on approximately the
same data
• minimizes traffic

Network (Cont.)
• generalized client-server model
• decoupling of network and game logic facilitates
extensibility
• network code can coordinate any game which can be described
by the language
• network is controlled on language level through keywords &
variables
• low level network (serialization, reliable UDP) done by core

Network - Basic Terminology
• Actor
• object that can move and interact with other actors

• Level
• object which contains a set of actors

• Game State
• the complete set of all actors that exist in a level
• the current values of all actor variables

Network – Update Loop
1. if (server)
Send(Gamestate) to all clients
2. if (client)
Send(RequestedMovement) to server
Receive(Gamestate) from server
Render(ApproximateWorldView) to screen
3. if (server || client)
Tick(DeltaTime) to update Gamestate
Update(Actors)
Execute(Physics)
Receive(GameEvents)
Execute(ScriptCode)

Actor Roles
• describes how much control the machine (server or
client) has over an actor
• controls the actors function call permissions
// Net variables.
enum ENetRole
{
ROLE_None,
ROLE_SimulatedProxy,
ROLE_AutonomousProxy,
ROLE_Authority,
};

//
//
//
//

No role at all.
Locally simulated proxy of this actor.
Locally autonomous proxy of this actor.
Authoritative control over the actor.

var ENetRole RemoteRole, Role;

Source: Actor.uc.

Bandwidth Optimization: Actor Relevancy
• eight prioritized rules:
•
•
•
•

not relevant, if (RemoteRole == none)
determined by the relevancy of its base, if any
relevant if (bAlwaysRelevant)
only potentially relevant to the client who owns that
Actor if (bOnlyRelevantToOwner)

Bandwidth Optimization: Actor Relevancy
• eight prioritized rules:
• relevant if (Owner==Player)
• not relevant if
• (bHidden) &&
• (!bBlockPlayers) &&
• (AmbientSound == none)

• relevant if visible according to a line-of-sight check
between the actor's Location and the player's

Location
• relevant, if was visible less than 2 to 10 seconds ago

Bandwidth Optimization: Prioritization
• Actor::NetPriority
• regulates share of the bandwidth based on how
important the Actor is to gameplay
• always relative to all other Actors’ NetPriority

Replication
• Actor replication
• only Location, Rotation valid on spawn

• variable replication
•
•
•
•

regulated by condition in Class Replication Statement
server to client only
always reliable
subject to bandwidth optimization
• repnotify keyword
replication
{
// replicate if server
if (Role == ROLE_Authority && (bNetInitial || bNetDirty))
Armor, Range, AttackDamage;
}

Source: HWPawn.uc.

Where‘s Waldo?
simulated event ReplicatedEvent(name VarName)
{
if (VarName == 'TeamIndex')
{
ChangeColor(TeamIndex);
}
}

Source: HWSelectable.uc, before January 11, 2011.

Where‘s Waldo?
simulated event ReplicatedEvent(name VarName)
{
if (VarName == 'TeamIndex')
{
ChangeColor(TeamIndex);
}
else
{
super.ReplicatedEvent(VarName);
}
}

Source: HWSelectable.uc.

Gotcha!

Never forget super calls when
overloading engine class functions!

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Replication
• function call replication
• keywords:
• server, client
• reliable, unreliable

• server -> client: only to client who owns that Actor
• client -> server: only on owned Actor
• immediately sent, disregarding bandwidth

reliable server function ServerIssueAbilityOrder(HWAIController C, HWAbility Ability, HWSelectable Target)

Source: HWPlayerController.uc.

Go ahead, …

… make something
Unreal!

References
• Epic Games. UDK Unreal Developer’s Kit.
http://www.unrealengine.com/udk/, October 2013.
• Epic Games. UDN Technical Home.
http://udn.epicgames.com/Three/TechnicalHome.html, October 2013.
• Epic Games. UDN UnrealScript Language Reference.
http://udn.epicgames.com/Three/UnrealScriptReference.html, October
2013.
• Epic Games. UDN AI & Navigation.
http://udn.epicgames.com/Three/ReplicationHome.html, October 2013.
• Epic Games. UDN Networking & Replication.
http://udn.epicgames.com/Three/ReplicationHome.html, October 2013.
• Epic Games. Epic Games Community Forum.
http://forums.epicgames.com/forums/366-UDK, October 2013.

63 / 58

Thank you for your attention!
Contact
Mail
dev@npruehs.de
Blog
http://www.npruehs.de
Twitter

@npruehs
Github
https://github.com/npruehs

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Introduction to the Unreal Development Kit

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