UMovementComponent::TwoWallAdjust

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#ue4 #c++ #移动组件

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本文介绍了一个虚拟环境中处理角色与两个墙面碰撞的算法。当角色在两个墙面之间移动时，通过计算调整移动方向来确保平滑的移动效果。该算法考虑了两墙面之间的夹角，并据此选择合适的移动方向。

void UCharacterMovementComponent::PhysFalling(float deltaTime, int32 Iterations)
{
		else if ( Hit.bBlockingHit )
		{	
			const FVector OldHitNormal = Hit.Normal;
				const FVector OldHitImpactNormal = Hit.ImpactNormal;				
				FVector Delta = ComputeSlideVector(Adjusted, 1.f - Hit.Time, OldHitNormal, Hit);
					// Move in deflected direction.
					SafeMoveUpdatedComponent( Delta, PawnRotation, true, Hit);
					
					if (Hit.bBlockingHit)
					{
						// hit second wall

						FVector PreTwoWallDelta = Delta;
						TwoWallAdjust(Delta, Hit, OldHitNormal);

在物理下落过程中，第一次碰撞后偏转移动过程，再次碰撞 hit seconde wall，调用TwoWallAdjust方法处理。

	/**
	 * Compute a movement direction when contacting two surfaces.
	 * @param Delta:		[In] Amount of move attempted before impact. [Out] Computed adjustment based on impacts.
	 * @param Hit:			Impact from last attempted move
	 * @param OldHitNormal:	Normal of impact before last attempted move
	 * @return Result in Delta that is the direction to move when contacting two surfaces.
	 */
	virtual void TwoWallAdjust(FVector &Delta, const FHitResult& Hit, const FVector &OldHitNormal) const;


void UMovementComponent::TwoWallAdjust(FVector& OutDelta, const FHitResult& Hit, const FVector& OldHitNormal) const
{
	FVector Delta = OutDelta;
	const FVector HitNormal = Hit.Normal;

	if ((OldHitNormal | HitNormal) <= 0.f) //90 or less corner, so use cross product for direction
	{
		const FVector DesiredDir = Delta;
		FVector NewDir = (HitNormal ^ OldHitNormal);
		NewDir = NewDir.GetSafeNormal();
		Delta = (Delta | NewDir) * (1.f - Hit.Time) * NewDir;
		if ((DesiredDir | Delta) < 0.f)
		{
			Delta = -1.f * Delta;
		}
	}
	else //adjust to new wall
	{
		const FVector DesiredDir = Delta;
		Delta = ComputeSlideVector(Delta, 1.f - Hit.Time, HitNormal, Hit);
		if ((Delta | DesiredDir) <= 0.f)
		{
			Delta = FVector::ZeroVector;
		}
		else if ( FMath::Abs((HitNormal | OldHitNormal) - 1.f) < KINDA_SMALL_NUMBER )
		{
			// we hit the same wall again even after adjusting to move along it the first time
			// nudge away from it (this can happen due to precision issues)
			Delta += HitNormal * 0.01f;
		}
	}

	OutDelta = Delta;
}

两个墙面夹角<=90°（等价于两个法向量夹角>=90°，二者点积 <= 0），判断两个法向量叉乘的方向（向量）是否可移动。

两个墙面夹角>90°（等价于两个法向量夹角<90°，二者点积 > 0），判断是否可向第二个墙面移动。