触屏设备上的多点触碰检测C++代码实现

转自：http://aigo.iteye.com/blog/2272698

代码还是参考自Epic官方的塔防项目：StrategyGame

看了下C++的API，现成的API中貌似只支持单点触碰检测，用法如下：
注册：

// support touch devices   
    InputComponent->BindTouch(EInputEvent::IE_Pressed, this, &ATD_MobilePlayerController::MoveToTouchLocation);  
    InputComponent->BindTouch(EInputEvent::IE_Repeat, this, &ATD_MobilePlayerController::MoveToTouchLocation);  

触发回调：

void ATD_MobilePlayerController::MoveToTouchLocation(const ETouchIndex::Type FingerIndex, const FVector Location)  
{  
    FVector2D ScreenSpaceLocation(Location);  
  
    // Trace to see what is under the touch location  
    FHitResult HitResult;  
    GetHitResultAtScreenPosition(ScreenSpaceLocation, CurrentClickTraceChannel, true, HitResult);  
    if (HitResult.bBlockingHit)  
    {  
        // We hit something, move there  
        SetNewMoveDestination(HitResult.ImpactPoint);  
    }  
}  

如果要实现多点触碰检测，比如实现两个手指捏动来缩放屏幕，StrategyGame项目自己实现了一套算法来实现多点屏幕检测，具体做法如下：
StrategyPlayerController.h

1，先重写StrategyPlayerController的ProcessPlayerInput()和SetupInputComponent()函数

protected:  
    /** update input detection */  
    virtual void ProcessPlayerInput(const float DeltaTime, const bool bGamePaused) override;  
    virtual void SetupInputComponent() override;  

在SetupInputComponent()函数中绑定事件（这个事件机制也是自己写的），其中BIND_1P_ACTION和BIND_2P_ACTION是自己定义的宏：

 

void AStrategyPlayerController::SetupInputComponent()  
{  
    Super::SetupInputComponent();  
  
    InputHandler = NewObject<UStrategyInput>(this);  
  
    BIND_1P_ACTION(InputHandler, EGameKey::Tap, IE_Pressed, &AStrategyPlayerController::OnTapPressed);  
    BIND_1P_ACTION(InputHandler, EGameKey::Hold, IE_Pressed, &AStrategyPlayerController::OnHoldPressed);  
    BIND_1P_ACTION(InputHandler, EGameKey::Hold, IE_Released, &AStrategyPlayerController::OnHoldReleased);  
    BIND_1P_ACTION(InputHandler, EGameKey::Swipe, IE_Pressed, &AStrategyPlayerController::OnSwipeStarted);  
    BIND_1P_ACTION(InputHandler, EGameKey::Swipe, IE_Repeat, &AStrategyPlayerController::OnSwipeUpdate);  
    BIND_1P_ACTION(InputHandler, EGameKey::Swipe, IE_Released, &AStrategyPlayerController::OnSwipeReleased);  
    BIND_2P_ACTION(InputHandler, EGameKey::SwipeTwoPoints, IE_Pressed, &AStrategyPlayerController::OnSwipeTwoPointsStarted);  
    BIND_2P_ACTION(InputHandler, EGameKey::SwipeTwoPoints, IE_Repeat, &AStrategyPlayerController::OnSwipeTwoPointsUpdate);  
    BIND_2P_ACTION(InputHandler, EGameKey::Pinch, IE_Pressed, &AStrategyPlayerController::OnPinchStarted);  
    BIND_2P_ACTION(InputHandler, EGameKey::Pinch, IE_Repeat, &AStrategyPlayerController::OnPinchUpdate);  
  
    FInputActionBinding& ToggleInGameMenuBinding = InputComponent->BindAction("InGameMenu", IE_Pressed, this, &AStrategyPlayerController::OnToggleInGameMenu);  
    ToggleInGameMenuBinding.bExecuteWhenPaused = true;  
  
}  

ProcessPlayerInput()来检测触碰点变化，这是一个连续执行的函数，大概逻辑是：每次执行时都会把当前的屏幕触碰信息和上次的触碰信息做对比，检测是单点触碰，还是按住不放，还是多点触碰或多点按住不放等等，具体逻辑在InputHandler->UpdateDetection(DeltaTime);中。

void AStrategyPlayerController::ProcessPlayerInput(const float DeltaTime, const bool bGamePaused)  
{  
    if (!bGamePaused && PlayerInput && InputHandler && !bIgnoreInput)  
    {  
        InputHandler->UpdateDetection(DeltaTime);  
    }  
  
    Super::ProcessPlayerInput(DeltaTime, bGamePaused);  
          
    if (!bIgnoreInput )  
    {  
        const ULocalPlayer* LocalPlayer = Cast<ULocalPlayer>(Player);  
        AStrategySpectatorPawn* StrategyPawn = GetStrategySpectatorPawn();        
        if(( StrategyPawn != NULL ) && ( LocalPlayer != NULL ))  
        {  
            // Create the bounds for the minimap so we can add it as a 'no scroll' zone.  
            AStrategyHUD* const HUD = Cast<AStrategyHUD>(GetHUD());  
            AStrategyGameState const* const MyGameState = GetWorld()->GetGameState<AStrategyGameState>();  
            if( (MyGameState != NULL ) && ( MyGameState->MiniMapCamera.IsValid() == true ) )  
            {  
                if( LocalPlayer->ViewportClient != NULL )  
                {  
                    const FIntPoint ViewportSize = LocalPlayer->ViewportClient->Viewport->GetSizeXY();  
                    const uint32 ViewTop = FMath::TruncToInt(LocalPlayer->Origin.Y * ViewportSize.Y);  
                    const uint32 ViewBottom = ViewTop + FMath::TruncToInt(LocalPlayer->Size.Y * ViewportSize.Y);  
  
                    FVector TopLeft( HUD->MiniMapMargin, ViewBottom - HUD->MiniMapMargin - MyGameState->MiniMapCamera->MiniMapHeight, 0 );  
                    FVector BottomRight( (int32)MyGameState->MiniMapCamera->MiniMapWidth, MyGameState->MiniMapCamera->MiniMapHeight, 0 );  
                    FBox MiniMapBounds( TopLeft, TopLeft + BottomRight );  
                    StrategyPawn->GetStrategyCameraComponent()->AddNoScrollZone( MiniMapBounds );  
                    StrategyPawn->GetStrategyCameraComponent()->UpdateCameraMovement( this );  
                }  
            }  
        }         
    }  
}  

StrategyInput.cpp

void UStrategyInput::UpdateDetection(float DeltaTime)  
{  
    UpdateGameKeys(DeltaTime);  
    ProcessKeyStates(DeltaTime);  
}  
  
void UStrategyInput::UpdateGameKeys(float DeltaTime)  
{  
    AStrategyPlayerController* MyController = CastChecked<AStrategyPlayerController>(GetOuter());  
  
    // gather current states  
    uint32 CurrentTouchState = 0;  
    for (int32 i = 0; i < ARRAY_COUNT(MyController->PlayerInput->Touches); i++)  
    {  
        if (MyController->PlayerInput->Touches[i].Z != 0)  
        {  
            CurrentTouchState |= (1 << i);  
        }  
    }  
  
    // detection  
    FVector2D LocalPosition1 = FVector2D(MyController->PlayerInput->Touches[0]);  
    FVector2D LocalPosition2 = FVector2D(MyController->PlayerInput->Touches[1]);  
  
    DetectOnePointActions(CurrentTouchState & 1, PrevTouchState & 1, DeltaTime, LocalPosition1, TouchAnchors[0], Touch0DownTime);  
    DetectTwoPointsActions((CurrentTouchState & 1) && (CurrentTouchState & 2), (PrevTouchState & 1) && (PrevTouchState & 2),  
        DeltaTime, LocalPosition1, LocalPosition2);  
  
    // save states  
    PrevTouchState = CurrentTouchState;  
}  
  
void UStrategyInput::ProcessKeyStates(float DeltaTime)  
{  
    for (const FActionBinding1P& AB : ActionBindings1P)  
    {  
        const FSimpleKeyState* KeyState = KeyStateMap.Find(AB.Key);  
  
        if (KeyState && KeyState->Events[AB.KeyEvent] > 0)  
        {  
            AB.ActionDelegate.ExecuteIfBound(KeyState->Position, KeyState->DownTime);  
        }  
    }  
  
    for (const FActionBinding2P& AB : ActionBindings2P)  
    {  
        const FSimpleKeyState* KeyState = KeyStateMap.Find(AB.Key);  
  
        if (KeyState && KeyState->Events[AB.KeyEvent] > 0)  
        {  
            AB.ActionDelegate.ExecuteIfBound(KeyState->Position, KeyState->Position2, KeyState->DownTime);  
        }  
    }  
  
    // update states  
    for (TMap<EGameKey::Type,FSimpleKeyState>::TIterator It(KeyStateMap); It; ++It)  
    {  
        FSimpleKeyState* const KeyState = &It.Value();  
  
        if (KeyState->Events[IE_Pressed])  
        {  
            KeyState->bDown = true;  
        }  
        else if (KeyState->Events[IE_Released])  
        {  
            KeyState->bDown = false;  
        }  
  
        FMemory::Memzero(KeyState->Events, sizeof(KeyState->Events));  
    }  
}