UE4 detecting which input method was last used by each player

InputModeDetector.cpp

#include "InputModeDetector.h"
#include "Input/Events.h"

FInputModeDetector::FInputModeDetector()
{
    // 4 local players should be plenty usually (will expand if necessary)
    LastInputModeByPlayer.Init(EInputMode::Mouse, 4);
}

bool FInputModeDetector::HandleKeyDownEvent(FSlateApplication& SlateApp, const FKeyEvent& InKeyEvent)
{
    // Key down also registers for gamepad buttons
    ProcessKeyOrButton(InKeyEvent.GetUserIndex(), InKeyEvent.GetKey());

    // Don't consume
    return false;
}

bool FInputModeDetector::HandleAnalogInputEvent(FSlateApplication& SlateApp,
    const FAnalogInputEvent& InAnalogInputEvent)
{
    if (InAnalogInputEvent.GetAnalogValue() > GamepadAxisThreshold)
        SetMode(InAnalogInputEvent.GetUserIndex(), EInputMode::Gamepad);
    // Don't consume
    return false;
}

bool FInputModeDetector::HandleMouseMoveEvent(FSlateApplication& SlateApp, const FPointerEvent& MouseEvent)
{
    FVector2D Dist = MouseEvent.GetScreenSpacePosition() - MouseEvent.GetLastScreenSpacePosition();
    if (FMath::Abs(Dist.X) > MouseMoveThreshold || FMath::Abs(Dist.Y) > MouseMoveThreshold)
    {
        SetMode(MouseEvent.GetUserIndex(), EInputMode::Mouse);
    }
    // Don't consume
    return false;
}

bool FInputModeDetector::HandleMouseButtonDownEvent(FSlateApplication& SlateApp, const FPointerEvent& MouseEvent)
{
    // We don't care which button
    SetMode(MouseEvent.GetUserIndex(), EInputMode::Mouse);
    // Don't consume
    return false;
}

bool FInputModeDetector::HandleMouseWheelOrGestureEvent(FSlateApplication& SlateApp, const FPointerEvent& InWheelEvent,
    const FPointerEvent* InGestureEvent)
{
    SetMode(InWheelEvent.GetUserIndex(), EInputMode::Mouse);
    // Don't consume
    return false;
}

void FInputModeDetector::Tick(const float DeltaTime, FSlateApplication& SlateApp, TSharedRef<ICursor> Cursor)
{
    // Required, but do nothing
}

EInputMode FInputModeDetector::GetLastInputMode(int PlayerIndex)
{
    if (PlayerIndex >= 0 && PlayerIndex < LastInputModeByPlayer.Num())
        return LastInputModeByPlayer[PlayerIndex];

    // Assume default if never told
    return DefaultInputMode;
}


void FInputModeDetector::ProcessKeyOrButton(int PlayerIndex, FKey Key)
{
    if (Key.IsGamepadKey())
    {
        SetMode(PlayerIndex, EInputMode::Gamepad);
    }
    else if (Key.IsMouseButton())
    {
        // Assuming mice don't have analog buttons!
        SetMode(PlayerIndex, EInputMode::Mouse);
    }
    else
    {
        // We assume anything that's not mouse and not gamepad is a keyboard
        // Assuming keyboards don't have analog buttons!
        SetMode(PlayerIndex, EInputMode::Keyboard);
    }
}
	
void FInputModeDetector::SetMode(int PlayerIndex, EInputMode NewMode)
{
    if (NewMode != EInputMode::Unknown && NewMode != GetLastInputMode(PlayerIndex))
    {
        if (PlayerIndex >= LastInputModeByPlayer.Num())
            LastInputModeByPlayer.SetNum(PlayerIndex + 1);
        
        LastInputModeByPlayer[PlayerIndex] = NewMode;
        OnInputModeChanged.ExecuteIfBound(PlayerIndex, NewMode);
        UE_LOG(LogTemp, Warning, TEXT("Input mode for player %d changed: %s"), PlayerIndex, *UEnum::GetValueAsString(NewMode));
    }
}

InputModeDetector.h

#pragma once

#include "CoreMinimal.h"
#include "InputCoreTypes.h"
#include "Framework/Application/IInputProcessor.h"

#include "UObject/ObjectMacros.h" // for UENUM

UENUM(BlueprintType)
enum class EInputMode : uint8
{
    Mouse,
    Keyboard,
    Gamepad,
    Unknown
};

DECLARE_DELEGATE_TwoParams(FOnInputModeForPlayerChanged, int /* PlayerIndex */, EInputMode)

/**
 * This class should be registered as an input processor in order to capture all input events & detect
 * what kind of devices are being used. We can't use PlayerController to do this reliably because in UMG
 * mode, all the mouse move events are consumed by Slate and you never see them, so it's not possible to
 * detect when the user moved a mouse.
 *
 * This class should be instantiated and used from some UObject of your choice, e.g. your GameInstance class,
 * something like this:
 *
 *    InputDetector = MakeShareable(new FInputModeDetector());
 *    FSlateApplication::Get().RegisterInputPreProcessor(InputDetector);
 *    InputDetector->OnInputModeChanged.BindUObject(this, &UMyGameInstance::OnInputDetectorModeChanged);
 *
 *    Note how the OnInputModeChanged on this object is a simple delegate, not a dynamic multicast etc, because
 *    this is not a UObject. You should relay the input mode event changed through the owner if you want to distribute
 *    the information further.
 */
class PROJECT_API FInputModeDetector : public IInputProcessor, public TSharedFromThis<FInputModeDetector>
{
protected:
    TArray<EInputMode> LastInputModeByPlayer;
    
public:

    EInputMode DefaultInputMode = EInputMode::Mouse;
    float MouseMoveThreshold = 1;
    float GamepadAxisThreshold = 0.2;

    // Single delegate caller, owner should propagate if they want (this isn't a UObject)
    FOnInputModeForPlayerChanged OnInputModeChanged;


    FInputModeDetector();

    virtual bool HandleKeyDownEvent(FSlateApplication& SlateApp, const FKeyEvent& InKeyEvent) override;
    virtual bool
    HandleAnalogInputEvent(FSlateApplication& SlateApp, const FAnalogInputEvent& InAnalogInputEvent) override;
    virtual bool HandleMouseMoveEvent(FSlateApplication& SlateApp, const FPointerEvent& MouseEvent) override;
    virtual bool HandleMouseButtonDownEvent(FSlateApplication& SlateApp, const FPointerEvent& MouseEvent) override;
    virtual bool HandleMouseWheelOrGestureEvent(FSlateApplication& SlateApp, const FPointerEvent& InWheelEvent,
        const FPointerEvent* InGestureEvent) override;


    virtual void Tick(const float DeltaTime, FSlateApplication& SlateApp, TSharedRef<ICursor> Cursor) override;

    EInputMode GetLastInputMode(int PlayerIndex = 0);

protected:
    void ProcessKeyOrButton(int PlayerIndex, FKey Key);
    void SetMode(int PlayerIndex, EInputMode NewMode);
};

UGameInstanceUsage.cpp

// You probably want to do this from your GameInstance subclass
...
// Namespace level in header
DECLARE_DYNAMIC_MULTICAST_DELEGATE_TwoParams(FOnInputModeChanged, int, PlayerIndex, EInputMode, InputMode);
...
// In class declaration:
protected:
    TSharedPtr<FInputModeDetector> InputDetector;  
public:
	/// Event raised when input mode changed between gamepad / keyboard / mouse
	UPROPERTY(BlueprintAssignable)
	FOnInputModeChanged OnInputModeChanged;

	UFUNCTION(BlueprintCallable)
	EInputMode GetLastInputModeUsed(int PlayerIndex = 0) const { return InputDetector->GetLastInputMode(PlayerIndex); }
	
	UFUNCTION(BlueprintCallable)
    bool LastInputWasGamePad(int PlayerIndex = 0) const { return GetLastInputModeUsed(PlayerIndex) == EInputMode::Gamepad; }

...

// In source
// Do this at startup somewhere
void MyExampleGameInstance::CreateInputDetector()
{
    if (!InputDetector.IsValid())
    {
        InputDetector = MakeShareable(new FInputModeDetector());
        FSlateApplication::Get().RegisterInputPreProcessor(InputDetector);

        InputDetector->OnInputModeChanged.BindUObject(this, &USnukaGameInstance::OnInputDetectorModeChanged);
    }

}

// Do this at shutdown
void MyExampleGameInstance::DestroyInputDetector()
{
    if (InputDetector.IsValid())
    {
        FSlateApplication::Get().UnregisterInputPreProcessor(InputDetector);
        InputDetector.Reset();
    }
}

void MyExampleGameInstance::OnInputDetectorModeChanged(int PlayerIndex, EInputMode NewMode)
{
    // Propagate dynamic multicast event, everyone else should listen on this
    OnInputModeChanged.Broadcast(PlayerIndex, NewMode);  
}

No. Local co-op exists, and input processors are global to the FSlateApplication.

Hi sinbad, I think that your theory is valid for legacy ue4 versions because I look at the source code and when we register an input processor it will add it to a list.

bool FSlateApplication::RegisterInputPreProcessor(TSharedPtr<IInputProcessor> InputProcessor, const int32 Index /*= INDEX_NONE*/)
{
	bool bResult = false;
	if ( InputProcessor.IsValid() )
	{
		bResult = InputPreProcessors.Add(InputProcessor, Index);
	}

	return bResult;
}

When a local player is created, a new HUD will be created as well, which means a new Input processor will be registered. I think I miss something but right now I do not understand why we need user index.

Ok I debug more. What I understand is that the application store all the number of local player. However every player create his own player controller, hud, game instance, etc...
I create and register the InputProcessor in the HUD which is created per player. This means that in my case I don't need to distinguish the player index. I hope my logic is correct, I'll be happy if someone can confirm my theory.
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I explored more the source code and result that InputProcessor is created in the SubSystem which has a unique instance (Singleton),