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PorgrammingGuideNotes_ProjectModuleClassOrg

  • AActor is base class Spawnable class

  • Component model: To Instantiate camera, can add CameraComponent to Actor object

Coding Standard:#

Reference From https://docs.unrealengine.com/latest/INT/Programming/Development/CodingStandard/index.html

  • Classes should have public interface methods declared first

  • Capitalize first letter of each word in variables

  • Types are prefixed with an additional capital letter (e.g. AActor):

  • T: Templates

  • U: Classes inheriting from Uobject

  • A: Classes inheriting from Aactor

  • S: Classes inheriting from Swidget

  • I: Abstract interfaces

  • F: Most other classes

  • E: Enums

  • Types/variables are nouns

  • Variables should be declared one at a time

  • Booleans should be prefixed with b

  • Methods are verbs that describe method’s effect or describe return value of method that has no effect. Strong verb followed by object (e.g. IsTeaFresh())

  • Prefix function parameters with Out if they are going to be modified. Const religion!

Portable Aliases for Basic C++ Types

  • bool for boolean values (NEVER assume the size of bool). BOOL will not compile.

  • TCHAR for a character (NEVER assume the size of TCHAR)

  • uint8 for unsigned bytes (1 byte)

  • int8 for signed bytes (1 byte)

  • uint16 for unsigned “shorts” (2 bytes)

  • int16 for signed “shorts” (2 bytes)

  • uint32 for unsigned ints (4 bytes)

  • int32 for signed ints (4 bytes)

  • uint64 for unsigned “quad words” (8 bytes)

  • int64 for signed “quad words” (8 bytes)

  • float for single precision floating point (4 bytes)

  • double for double precision floating point (8 bytes)

  • PTRINT for an integer that may hold a pointer (NEVER assume the size of PTRINT)

Don’t use the C++ int type in portable code, since it’s dependent on the compiler how large it is.

General#

  • Comment third party code with special comments
// @third party code - BEGIN PhysX
#include <PhysX.h>
// @third party code - END PhysX
  • Braces should be on a new line

  • Minimize file-coupling by using forward declarations instead of include headers when possible

  • Use #pragma once

  • Fine-grained header inclusion: Include every header you need directl. Don’t rely on a header that is included indirectly by another header you include

  • Place definitions needed by other modules in the Public directory of a module. Everything else should be in the Private directory. (Old UE modules use Src/Inc for this distinction).

  • Never allow float to implicit convert to int32 b/c it’s slow. Always use the appTrunc() function to convert to int32. This will ensure cross-compiler compatibility as well as generate faster code.

  • Interface classes (prefixed with “I”) should always be abstract and must not have member variables. Interfaces are allowed to contain methods that are not pure-virtual, and even methods that are non-virtual or static, as long as they are implemented inline.

  • Use const wherever possible. Particularly on reference parameters and class methods. const is documentation as much as it is a compiler directive.

  • Pointers & references declared with one space. Ex: FShaderType* Type

  • Use virtual & OVERRIDE when defining derived functions.

  • Leave a blank line at the end of the file. All .cpp and .h files for gcc

Namespaces

You can use namespaces to organize your classes, functions and variables where appropriate, as long as you follow the rules below.

  • Don’t use “using” declarations in the global scope, even in .cpp files

  • You can use “using” inside of another namespace or inside functions

  • Note that if you put “using” within a namespace, it will carry over to other occurrences of that namespace in the same translation unit. As long as you’re consistent it will be fine, though.

  • You can only use “using” in header files safely if you follow the above rules.

  • Enums must be wrapped in their own namespace b/c C++ Enum values have the same scope. Ex:

 /** Defining a enumeration within a namespace to achieve C#-style enum scoping */
 namespace EColorChannel
 {
 /** Declare EColorChannel::Type as the actual type for this enum */
 enum Type
 {
 Red,
 Green,
 Blue
 };
 }

 /** Given a color channel, returns the name of that channel. */
 FString GetNameForColorChannel(const EColorChannel::Type ColorChannel)
 {
 switch(ColorChannel)
 {
 case EColorChannel::Red: return TEXT("Red");
 case EColorChannel::Green: return TEXT("Green");
 case EColorChannel::Blue: return TEXT("Blue");
 default: return TEXT("Unknown");
 }
 }
  • Note that for locally-declared enums, you won’t be able to use a namespace for scoping. In these cases, we opt to declare a local struct with no member variables, only a local enum type and use that struct for scoping.
  /** Defining a locally-scoped enumeration using structs*/
  class FObjectMover
  {
  public:

  /** Direction to move */
  struct EMoveDirection
  {
  enum Type
  {
  Forward,
  Reverse,
  };
  };

/** Construct an FObjectMover with the specified movement direction */
FObjectMover( const EMoveDirection::Type Direction );

Reference From https://docs.unrealengine.com/latest/INT/Programming/Development/CodingStandard/index.html

Object Handling#

UCLASS() macro tags classes into the Uobject handling system:

  • Gives class a reference to UClass object

  • UClass Object is UE4 C++ implementation of attribute decorators/rtti

  • UClass Object contains reference to CDO, class default object.

  • UClass macros also used to decorate functions & properties

Object Creation#

There are several functions that can be used to create new UObject instances as well as the standard new operator; each of which have their own use case:

Method Description
NewObject() Creates a new instance with an automatically generated name. Best practice to use for simple cases.
NewNamedObject() Creates a new instance using a specified name along with a few other optional parameters. Asserts if the name conflicts within the new instance’s Outer.
ConstructObject() Creates a new instance providing all available creation options. Use only when flexibility is required.
new Use to construct objects in certain low level circumstances, such as when the constructor requires arguments.

Reference From https://docs.unrealengine.com/latest/INT/Programming/UnrealArchitecture/Objects/index.html

  • Tick is the Update() per frame update function.

  • Must derive from FTickableGameObject to make a class tickable

UClass System notes:

  • UClass is the C++ class that contains the RTTI info

  • UE4 implements a Garbage collection system

  • Auto-initialization for properties

  • Auto-serialization. Will auto-update values in the level if they’ve not been manually overridden in the CDO

  • Automatic editor integration

  • Simple RTTI (can do typecasting IsA() or Cast()

  • Supports network replication (can tag UFUNCTIONS for RPC & UPROPERTIES for replication)

Misc#

  • Frameroot smoothing = Sets MaxTick() to be running average of last 300 frames, clamped to MinSmoothFramerate & MaxSmoothFramerate

Actors#

  • Not garbage collected (b/c World object holds references to all actors)

  • Can be explicitly destroyed by calling Destroy()

  • Creating new actors done with SpawnActor()

  • Handles replication of properties & functions

  • Functionality exposed through component pattern. Actors contain no xform or basic data

  • Tick function is TickActor()

  • Spawned with UWorld::SpawnActor()

  • More spawning helper functions @ https://docs.unrealengine.com/latest/INT/Programming/UnrealArchitecture/Actors/Spawning/index.html

Components#

  • UActorComponent: Base class for components

  • USceneComponent: Base component that contains xform

  • UPrimitiveComponent: Component made up of other things (mesh, particles, etc)

  • CapsuleComponents generate geometry for collision detection

  • StaticMeshComponents for static geo

  • SkeletalMeshComponents for collision detection

  • Components must be registered UActorComponent::RegisterComponent()

  • Components tick through TickComponent() (Ex: SkeletalMesh calls TickComponent() to update animation & skeletal controllers)

  • RenderState manages rendering for a component

  • PhysicsState manages physics for a component

Register Events

When a component is registered, the events below are fired off.

Function Description
UActorComponent::OnRegister() Event to allow for additional initialization when registering a component, if necessary.
UActorComponent::CreateRenderState() Initializes the render state for the component.
UActorComponent::CreatePhysicsState() Initializes the physics state for the component.

UnRegistering Components#

ActorComponents can be unregistered as well to avoid them being updated, simulated, or rendered. Unregistering a component is performed by callingUActorComponent::UnregisterComponent().

void UActorComponent::UnregisterComponent()

UnRegister Events

The events below are fired off when a component is unregistered.

Function Description
UActorComponent::OnUnRegister() Event to allow for additional actions when unregistering a component, if necessary.
UActorComponent::DestroyRenderState() Uninitializes the render state for the component.
UActorComponent::DestroyPhysicsState() Uninitializes the physics state for the component.

Reference From https://docs.unrealengine.com/latest/INT/Programming/UnrealArchitecture/Actors/Components/index.html

Component Transforms

  • FTransform struct contains a Translation vector, a Rotation quaternion, and a Scale3D vector.

  • They also have an additional RelativeLocation vector,RelativeRotation rotator, and RelativeScale3D vector

  • Can be relative to world or parent

  • Generally used for getting & setting transform for a component

  • Default relative to AttachParent. Control relative by setting bAbsoluteLocation, bAbsoluteRotation, and bAbsoluteScale properties

  • Can also set the absolute world position (internally converted to relative xform) by these functions

Function Description
SceneComponent::SetWorldLocation() Set the relative translation of this component to put it at the supplied location in world space.
SceneComponent::SetWorldRotation() Set the relative rotation of this component to put it at the supplied orientation in world space.

Reference From https://docs.unrealengine.com/latest/INT/Programming/UnrealArchitecture/Actors/Components/index.html

Delegates

Delegates allow you to call member functions on C++ objects in a generic, yet type-safe way. Using delegates, you can dynamically bind to a member function of an arbitrary object, then call functions on the object, even if the caller does not know the object’s type.

It is perfectly safe to copy delegate objects. Delegates can be passed around by value but this is generally not recommended since they do have to allocate memory on the heap. You should always pass delegates by reference when possible.

Both single-cast and multi-cast delegates are supported, as well as “dynamic” delegates which can be safely serialized to disk.

See the Delegates page for reference and usage information.

Reference From https://docs.unrealengine.com/latest/INT/Programming/UnrealArchitecture/Reference/Functions/index.htm


Last update: November 14, 2019