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C++ inputs.md

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2020-12-31_17:03:18

C++ inputs

The virtual member functions APawn::SetPlayerInputComponent and APlayerController::SetupInputComponent are called at the start of the game. Called after the Pawn constructor and before Begin Play. The Pawn version is passed an UInputComponent. The Player Controller has a member named InputComponent UInputComponent is used to bind input events to function callbacks.

The functions we bind should have these signatures:

  • Action event: void().
  • Axis event: void(float).

I believe Delegates, or some related object, can be used to make functions with other signatures look like it has these signatures. [[2021-03-10_10:42:34]] Delegate

A member function is bound to a named input action event with BindAction.

FInputActionBinding& UInputComponent::BindAction(
    FName ActionName, EInputEvent KeyEvent, UserClass* Object, FInputActionHandlerSignature Function);

A member function is bound to a named input axis event with BindAxis.

FInputAxisBinding& UInputComponent::BindAction(
    FName AxisName, UserClass* Object, FInputActionHandlerSignature Function);

The names ActionName and AxisName must be input actions defined in Project Settings > Engine > Input > Bindings. The EInputEvent KeyEvent is either IE_Pressed or IE_Released. Object is a pointer to the object that should receive the callback. Function is a pointer to the member function that should be called.

An example SetupPlayerInputComponent implementation:

UCLASS()
class AMyPawn : public APawn
{
public:
    GENERATED_BODY()

    virtual void SetupPlayerInputComponent(UInputComponent* Input);

    void OnInteractStart();
    void OnInteractEnd();
    void OnForward(float Value);
    void OnRight(float Value);
};

void AMyPawn::SetupPlayerInputComponent(UInputComponent* Input)
{
    Super::SetupPlayerInputComponent(Input);

    Input->BindAction("Interact", IE_Pressed, this, &AMyPawn::OnInteractStart);
    Input->BindAction("Interact", IE_Released, this, &AMyPawn::OnInteractEnd);

    Input->BindAxis("Forward", this, &AMyPawn::OnForward);
    Input->BindAxis("Right", this, &AMyPawn::OnRight);
}

Some configuration can be made on the binding references returned by BindAction and BindAxis. For example enable or disable consume input.

void AMyPawn::SetupPlayerInputComponent(UInputComponent* Input)
{
    Super::SetupPlayerInputComponent(Input);
    FInputAxisBinding& InteractStartBinding =
        Input->BindAction("Interact", IE_Pressed, this, &AMyPawn::OnInteractStart);
    InteractStartBinding.bConsumeInput = false;
}

Input Processor

There is something called an Input Processor. Don't know much about it, but it is created and registered with

auto InputProcessor = MakeShareable(new FMyInputProcessor(this)); FSlateApplication::Get().RegisterInputPreProcessor(InputProcessor);

where MyInputProcessor implements IInputProcessor.

[[2020-04-10_21:46:17]] Inputs
[[2021-01-01_16:41:46]] C++ Pawn
[[2021-01-03_17:40:41]] C++ Character
[[2020-04-11_11:27:52]] PlayerController