tengri/Source/TengriPlatformer/Movement/TengriMovementComponent.cpp

// Request Games © All rights reserved

// Source/TengriPlatformer/Movement/TengriMovementComponent.cpp

#include "TengriMovementComponent.h"
#include "Components/CapsuleComponent.h"
#include "TengriPlatformer/Movement/Collision/TengriCollisionResolver.h"

DEFINE_LOG_CATEGORY_STATIC(LogTengriMovement, Log, All);

// ============================================================================
//                             CONSTANTS
// ============================================================================

namespace TengriMovement
{
	// Maximum physics iterations per frame (prevents infinite loop)
	constexpr int32 MaxPhysicsIterationsPerFrame = 5;

	// Ground snapping thresholds
	constexpr float FastFallThreshold = -200.0f;  // cm/s, skip snap when falling fast
	constexpr float JumpingThreshold = 10.0f;     // cm/s, skip snap when moving up
}

// ============================================================================
//                        PENDING EVENTS (NEW)
// ============================================================================

/** 
 * Structure to accumulate events during physics loop.
 * These are broadcasted AFTER all physics iterations complete.
 */
struct FPendingLandingEvent
{
	bool bIsHeavy;
	float LandingVelocityZ;
};

// ============================================================================
//                           CONSTRUCTOR
// ============================================================================

UTengriMovementComponent::UTengriMovementComponent()
{
	PrimaryComponentTick.bCanEverTick = true;
	Velocity = FVector::ZeroVector;
	bIsGrounded = false;
}

// ============================================================================
//                          INITIALIZATION
// ============================================================================

void UTengriMovementComponent::BeginPlay()
{
	Super::BeginPlay();
	InitializeSystem();
}

void UTengriMovementComponent::InitializeSystem()
{
	const AActor* Owner = GetOwner();
	if (!Owner)
	{
		UE_LOG(LogTengriMovement, Error, TEXT("InitializeSystem failed: No owner"));
		SetComponentTickEnabled(false);
		return;
	}

	OwnerCapsule = Cast<UCapsuleComponent>(Owner->GetRootComponent());
	if (!OwnerCapsule)
	{
		UE_LOG(LogTengriMovement, Error,
			TEXT("InitializeSystem failed: Owner root component is not a CapsuleComponent"));
		SetComponentTickEnabled(false);
		return;
	}

	if (!MovementConfig)
	{
		UE_LOG(LogTengriMovement, Warning,
			TEXT("InitializeSystem: No MovementConfig assigned"));
		return;
	}

	// Cache thresholds
	CachedThresholds = MovementConfig->GetThresholds();

	// Initialize fixed timestep parameters from config
	FixedTimeStep = 1.0f / MovementConfig->PhysicsTickRate;
	MaxAccumulatorTime = MovementConfig->MaxAccumulatedTime;
	TimeAccumulator = 0.0f;

	// Initialize physics state from current actor transform
	PhysicsLocation = Owner->GetActorLocation();
	PhysicsRotation = Owner->GetActorRotation();
	PhysicsVelocity = FVector::ZeroVector;

	// Initialize render state to match physics (no interpolation on first frame)
	RenderLocation = PhysicsLocation;
	RenderRotation = PhysicsRotation;
	PreviousPhysicsLocation = PhysicsLocation;
	PreviousPhysicsRotation = PhysicsRotation;

	UE_LOG(LogTengriMovement, Log,
		TEXT("System initialized. WalkableZ: %.3f, PhysicsRate: %.0f Hz, FixedStep: %.4f s"),
		CachedThresholds.WalkableZ,
		MovementConfig->PhysicsTickRate,
		FixedTimeStep);
}

// ============================================================================
//                           BLUEPRINT API
// ============================================================================

void UTengriMovementComponent::SetInputVector(const FVector NewInput)
{
	InputVector = NewInput.GetClampedToMaxSize(1.0f);
	InputVector.Z = 0.0f;
}

void UTengriMovementComponent::SetJumpInput(const bool bPressed)
{
	if (bPressed && !bIsJumpHeld)
	{
		if (MovementConfig)
		{
			JumpBufferTimer = MovementConfig->JumpBufferTime;
		}
	}
	
	bIsJumpHeld = bPressed;
}

// ============================================================================
//                              TICK
// ============================================================================

void UTengriMovementComponent::TickComponent(
	const float DeltaTime,
	const ELevelTick TickType,
	FActorComponentTickFunction* ThisTickFunction)
{
	Super::TickComponent(DeltaTime, TickType, ThisTickFunction);

	if (!MovementConfig || !OwnerCapsule)
	{
		return;
	}

	// ════════════════════════════════════════════════════════════════════
	//                  FIXED TIMESTEP ACCUMULATION
	// ════════════════════════════════════════════════════════════════════

	TimeAccumulator += DeltaTime;

	// Clamp accumulator to prevent "spiral of death"
	if (TimeAccumulator > MaxAccumulatorTime)
	{
		UE_LOG(LogTengriMovement, Warning,
			TEXT("TimeAccumulator clamped: %.3f -> %.3f (frame took too long)"),
			TimeAccumulator, MaxAccumulatorTime);
		TimeAccumulator = MaxAccumulatorTime;
	}

	// ════════════════════════════════════════════════════════════════════
	//              PENDING EVENTS (Accumulated during physics)
	// ════════════════════════════════════════════════════════════════════

	TArray<FPendingLandingEvent> PendingLandings;

	// ════════════════════════════════════════════════════════════════════
	//                  DETERMINISTIC PHYSICS LOOP
	// ════════════════════════════════════════════════════════════════════

	int32 PhysicsIterations = 0;

	while (TimeAccumulator >= FixedTimeStep)
	{
		// Save state for interpolation BEFORE physics step
		SavePreviousPhysicsState();

		// Run deterministic physics at fixed rate
		// Pass reference to PendingLandings to accumulate events
		TickPhysics(FixedTimeStep, PendingLandings);

		// Consume fixed time from accumulator
		TimeAccumulator -= FixedTimeStep;
		PhysicsIterations++;

		// Safety: prevent runaway loop
		if (PhysicsIterations >= TengriMovement::MaxPhysicsIterationsPerFrame)
		{
			UE_LOG(LogTengriMovement, Warning,
				TEXT("Max physics iterations reached (%d), discarding remaining time"),
				TengriMovement::MaxPhysicsIterationsPerFrame);
			TimeAccumulator = 0.0f;
			break;
		}
	}

	// ════════════════════════════════════════════════════════════════════
	//                  BROADCAST ACCUMULATED EVENTS
	// ════════════════════════════════════════════════════════════════════

	// Only broadcast the LAST landing event if multiple occurred
	// (Prevents spam if character lands multiple times in one frame)
	if (PendingLandings.Num() > 0)
	{
		const FPendingLandingEvent& LastLanding = PendingLandings.Last();
		if (OnLanded.IsBound())
		{
			OnLanded.Broadcast(LastLanding.bIsHeavy);
		}

		if (LastLanding.bIsHeavy)
		{
			UE_LOG(LogTengriMovement, Verbose,
				TEXT("Heavy landing detected! Velocity: %.1f cm/s"),
				LastLanding.LandingVelocityZ);
		}
	}

	// ════════════════════════════════════════════════════════════════════
	//                  INTERPOLATION & RENDERING
	// ════════════════════════════════════════════════════════════════════

	if (MovementConfig->bEnableInterpolation && PhysicsIterations > 0)
	{
		// Calculate interpolation factor [0..1]
		const float Alpha = TimeAccumulator / FixedTimeStep;
		InterpolateRenderState(Alpha);
	}
	else
	{
		// No interpolation: use physics state directly
		RenderLocation = PhysicsLocation;
		RenderRotation = PhysicsRotation;
	}

	// Apply visual transform to actor
	ApplyRenderState();

	// Sync public Velocity for Blueprint access
	Velocity = PhysicsVelocity;
}

// ============================================================================
//                          PHYSICS TICK
// ============================================================================

void UTengriMovementComponent::TickPhysics(
	const float FixedDeltaTime,
	TArray<FPendingLandingEvent>& OutPendingLandings)
{
    // ════════════════════════════════════════════════════════════════════
    //                  Phase 0: State & Timer Updates
    // ════════════════════════════════════════════════════════════════════

    // 1. Manage Coyote Time (Can we jump while falling?)
    if (bIsGrounded)
    {
        CoyoteTimer = MovementConfig->CoyoteTime;
        bHasJumpedThisFrame = false;
    }
    else
    {
        CoyoteTimer -= FixedDeltaTime;
    }

    // 2. Manage Jump Buffer (Did we press jump recently?)
    if (JumpBufferTimer > 0.0f)
    {
        JumpBufferTimer -= FixedDeltaTime;
    }

    // ════════════════════════════════════════════════════════════════════
    //                  Phase 1: Jump Execution
    // ════════════════════════════════════════════════════════════════════

    // Check if we can jump:
    // 1. Button was pressed recently (Buffer > 0)
    // 2. We are on ground OR recently left ground (Coyote > 0)
    // 3. We haven't already jumped this frame (double jump prevention)
    if (JumpBufferTimer > 0.0f && CoyoteTimer > 0.0f && !bHasJumpedThisFrame)
    {
        // Apply Jump Velocity
        PhysicsVelocity.Z = MovementConfig->JumpVelocity;
        
        // Update State
        bIsGrounded = false;
        bHasJumpedThisFrame = true;
        
        // Consume Timers
        JumpBufferTimer = 0.0f;
        CoyoteTimer = 0.0f;
    }

    // ════════════════════════════════════════════════════════════════════
    //                  Phase 2: Variable Jump Height
    // ════════════════════════════════════════════════════════════════════

    // If moving up AND button released -> Cut velocity
    if (PhysicsVelocity.Z > MovementConfig->MinJumpVelocity && !bIsJumpHeld)
    {
        PhysicsVelocity.Z = MovementConfig->MinJumpVelocity;
    }

    // ════════════════════════════════════════════════════════════════════
    //                  Phase 3: Horizontal Movement (Air Control)
    // ════════════════════════════════════════════════════════════════════

    const float CurrentZ = PhysicsVelocity.Z;
    FVector HorizontalVelocity(PhysicsVelocity.X, PhysicsVelocity.Y, 0.f);

    const float CurrentFriction = bIsGrounded 
        ? MovementConfig->Friction 
        : MovementConfig->AirFriction;

    if (!InputVector.IsNearlyZero())
    {
        // Calculate directional air control modifier
        // Reduce control when trying to reverse direction mid-air
        const FVector VelocityDir = HorizontalVelocity.GetSafeNormal();
        const float Dot = FVector::DotProduct(VelocityDir, InputVector);
        
        float FinalAirControl = MovementConfig->AirControl;
        
        // Reduce braking effectiveness in air (prevents instant direction changes)
        if (Dot < 0.0f)
        {
            FinalAirControl *= 0.5f;
        }

        const float CurrentAccel = MovementConfig->Acceleration * FinalAirControl;
        const FVector TargetVelocity = InputVector * MovementConfig->MaxSpeed;

        if (CurrentAccel > KINDA_SMALL_NUMBER)
        {
            HorizontalVelocity = FMath::VInterpTo(
                HorizontalVelocity,
                TargetVelocity,
                FixedDeltaTime,
                CurrentAccel
            );
        }
    }
    else
    {
        if (CurrentFriction > KINDA_SMALL_NUMBER)
        {
            HorizontalVelocity = FMath::VInterpTo(
                HorizontalVelocity,
                FVector::ZeroVector,
                FixedDeltaTime,
                CurrentFriction
            );
        }
    }

    PhysicsVelocity = HorizontalVelocity;
    PhysicsVelocity.Z = CurrentZ;

	// ════════════════════════════════════════════════════════════════════
	//                  Phase 4: Rotation
	// ════════════════════════════════════════════════════════════════════

	FRotator TargetRot = PhysicsRotation; // Default: maintain current rotation
	bool bShouldUpdateRotation = false;
	float CurrentRotSpeed = MovementConfig->RotationSpeed;

	// SCENARIO A: STRAFE MODE (Aiming)
	// Character rotates to match camera even when stationary.
	// Used for combat/precise aiming scenarios.
	if (bStrafing)
	{
		if (const APawn* PawnOwner = Cast<APawn>(GetOwner()))
		{
			if (const AController* C = PawnOwner->GetController())
			{
				TargetRot = C->GetControlRotation();
				bShouldUpdateRotation = true;
                
				// Optional: Faster rotation in combat for responsive feel
				CurrentRotSpeed *= 2.0f; 
			}
		}
	}
	// SCENARIO B: STANDARD MOVEMENT (Classic platformer)
	// Character rotates toward velocity direction only when moving.
	// Maintains forward orientation based on movement.
	else 
	{
		if (const float MinSpeedSq = FMath::Square(MovementConfig->MinSpeedForRotation); PhysicsVelocity.SizeSquared2D() > MinSpeedSq)
		{
			TargetRot = PhysicsVelocity.ToOrientationRotator();
			bShouldUpdateRotation = true;
		}
	}

	// APPLY ROTATION
	if (bShouldUpdateRotation)
	{
		// Always prevent pitch/roll to keep character upright
		TargetRot.Pitch = 0.0f;
		TargetRot.Roll = 0.0f;

		PhysicsRotation = FMath::RInterpConstantTo(
			PhysicsRotation,
			TargetRot,
			FixedDeltaTime,
			CurrentRotSpeed
		);
	}

    // ════════════════════════════════════════════════════════════════════
    //                  Phase 5: Gravity
    // ════════════════════════════════════════════════════════════════════

    if (!bIsGrounded)
    {
        float CurrentGravity = MovementConfig->Gravity;

        // Apply extra gravity if falling (makes jump snappy)
        if (PhysicsVelocity.Z < 0.0f)
        {
            CurrentGravity *= MovementConfig->FallingGravityScale;
        }

        PhysicsVelocity.Z -= CurrentGravity * FixedDeltaTime;

        // Clamp to terminal velocity
        if (PhysicsVelocity.Z < -MovementConfig->TerminalVelocity)
        {
            PhysicsVelocity.Z = -MovementConfig->TerminalVelocity;
        }
    }

    // ════════════════════════════════════════════════════════════════════
    //                  Phase 6: Collision Resolution
    // ════════════════════════════════════════════════════════════════════

    const FVector DesiredDelta = PhysicsVelocity * FixedDeltaTime;

    const FTengriSweepResult MoveResult = UTengriCollisionResolver::ResolveMovement(
        this,
        PhysicsLocation,
        DesiredDelta,
        OwnerCapsule,
        CachedThresholds,
        MovementConfig->MaxStepHeight,
        MovementConfig->MaxSlideIterations
    );

    PhysicsLocation = MoveResult.Location;

    // ════════════════════════════════════════════════════════════════════
    //                  Phase 7: Ground Snapping
    // ════════════════════════════════════════════════════════════════════

    bool bJustSnapped = false;

    // Only snap if we are NOT jumping upwards
    if (PhysicsVelocity.Z <= 0.0f) 
    {
        FHitResult SnapHit;
        bJustSnapped = PerformGroundSnapping(PhysicsLocation, SnapHit);
        
        // Always project velocity onto slope when snapped (preserves momentum)
        if (bJustSnapped)
        {
            PhysicsVelocity = UTengriCollisionResolver::ProjectVelocity(
                PhysicsVelocity,
                SnapHit.ImpactNormal
            );
        }
    }

    // ════════════════════════════════════════════════════════════════════
    //                  Phase 8: State Update
    // ════════════════════════════════════════════════════════════════════

    const bool bWasGrounded = bIsGrounded;
    
    // We are grounded if:
    // 1. We snapped to ground, OR
    // 2. We hit a walkable surface during movement
    const bool bHitWalkable = MoveResult.bBlocked &&
        CachedThresholds.IsWalkable(MoveResult.Hit.ImpactNormal.Z);

    const bool bNowGrounded = bJustSnapped || bHitWalkable;

    // ════════════════════════════════════════════════════════════════════
    //                  Phase 9: Landing Detection
    // ════════════════════════════════════════════════════════════════════

    if (!bWasGrounded && bNowGrounded)
    {
        // Store landing velocity BEFORE we zero it
        const float LandingVelocityZ = PhysicsVelocity.Z;
        const bool bIsHeavy = LandingVelocityZ < MovementConfig->HeavyLandVelocityThreshold;
        
        // Accumulate event instead of broadcasting immediately
        FPendingLandingEvent LandingEvent;
        LandingEvent.bIsHeavy = bIsHeavy;
        LandingEvent.LandingVelocityZ = LandingVelocityZ;
        OutPendingLandings.Add(LandingEvent);
    }

    // Update grounded state
    bIsGrounded = bNowGrounded;

    // Reset Z velocity if we landed or are on ground
    if (bIsGrounded && PhysicsVelocity.Z < 0.f)
    {
        PhysicsVelocity.Z = 0.f;
    }
}

// ============================================================================
//                       INTERPOLATION
// ============================================================================

void UTengriMovementComponent::SavePreviousPhysicsState()
{
	PreviousPhysicsLocation = PhysicsLocation;
	PreviousPhysicsRotation = PhysicsRotation;
}

void UTengriMovementComponent::InterpolateRenderState(float Alpha)
{
	Alpha = FMath::Clamp(Alpha, 0.0f, 1.0f);

	// Linear interpolation for location
	RenderLocation = FMath::Lerp(PreviousPhysicsLocation, PhysicsLocation, Alpha);

	// Lerp for rotation (FMath::Lerp handles FRotator correctly)
	RenderRotation = FMath::Lerp(PreviousPhysicsRotation, PhysicsRotation, Alpha);
}

void UTengriMovementComponent::ApplyRenderState() const
{
	if (AActor* Owner = GetOwner())
	{
		Owner->SetActorLocation(RenderLocation, false, nullptr, ETeleportType::None);
		Owner->SetActorRotation(RenderRotation, ETeleportType::None);
	}
}

// ============================================================================
//                       GROUND SNAPPING
// ============================================================================

bool UTengriMovementComponent::PerformGroundSnapping(
	FVector& InOutLocation,
	FHitResult& OutSnapHit) const
{
	// Skip snap when clearly airborne intentionally
	const bool bIsFallingFast = PhysicsVelocity.Z < TengriMovement::FastFallThreshold;

	if (const bool bIsJumping = PhysicsVelocity.Z > TengriMovement::JumpingThreshold; !bIsGrounded && (bIsFallingFast || bIsJumping))
	{
		return false;
	}

	// Use physics location as start point (NOT render position!)
	const FVector Start = InOutLocation;
	const FVector End = Start - FVector(0.f, 0.f, MovementConfig->GroundSnapDistance);

	const FTengriSweepResult Sweep = UTengriCollisionResolver::PerformSweep(
		this,
		Start,
		End,
		OwnerCapsule
	);

	if (Sweep.bBlocked && CachedThresholds.IsWalkable(Sweep.Hit.ImpactNormal.Z))
	{
		// Apply micro-offset to prevent floor penetration
		InOutLocation = Sweep.Location + FVector(0.f, 0.f, MovementConfig->GroundSnapOffset);
		OutSnapHit = Sweep.Hit;
		return true;
	}

	return false;
}

void UTengriMovementComponent::ForceRotation(const FRotator& NewRotation)
{
	// Update all internal states so physics adopts new rotation immediately
	PhysicsRotation = NewRotation;
	RenderRotation = NewRotation;
	PreviousPhysicsRotation = NewRotation; // Reset interpolation
}