kDOP.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "CoreMinimal.h"
#include "Containers/ChunkedArray.h"
#include "Templates/UnrealTemplate.h"
#include <limits>
 
// Indicates how many "k / 2" there are in the k-DOP. 3 == AABB == 6 DOP. The code relies on this being 3.
#define NUM_PLANES  3
 
template <typename COLL_DATA_PROVIDER, typename KDOP_IDX_TYPE> struct TkDOPLineCollisionCheck;
 
struct FkHitResult
{
    FVector4    Normal;
    float       Time;
    int32           Item;       
 
    FkHitResult()
    : Normal    (0,0,0,0)
    , Time      (1.0f)
    , Item      (INDEX_NONE)
    {
    }
};
 
struct FVector3SOA
{
    VectorRegister  X;
    VectorRegister  Y;
    VectorRegister  Z;
};
 
struct FVector4SOA
{
    VectorRegister  X;
    VectorRegister  Y;
    VectorRegister  Z;
    VectorRegister  W;
};
 
struct FTriangleSOA
{
    FVector3SOA Positions[3];
    FVector4SOA Normals;
    uint32      Payload[4];
};
 
template<typename KDOP_IDX_TYPE>
struct TTraversalHistory
{
    enum { NodeHistoryLength = 1 };
    KDOP_IDX_TYPE Nodes[NodeHistoryLength];
 
    TTraversalHistory()
    {
        for (int32 NodeIndex = 0; NodeIndex < NodeHistoryLength; NodeIndex++)
        {
            // Initialize the history to invalid index
            Nodes[NodeIndex] = 0xFFFFFFFF;
        }
    }
 
    TTraversalHistory AddNode(KDOP_IDX_TYPE NewNodeIndex) const
    {
        TTraversalHistory NewHistory;
        // Move all the indices toward the end of the array one element
        CopyAssignItems(NewHistory.Nodes + 1, Nodes, NodeHistoryLength - 1);
        // Insert the new node at the beginning of the array
        NewHistory.Nodes[0] = NewNodeIndex;
        return NewHistory;
    }
 
    KDOP_IDX_TYPE GetOldestNode() const
    {
        // Accesses the oldest node that this traversal history is tracking
        return Nodes[NodeHistoryLength - 1];
    }
};
 
FORCEINLINE bool appLineCheckTriangle(const FVector4& Start, const FVector4& End, const FVector4& Dir, const FVector4& V0, const FVector4& V1, const FVector4& V2, const FVector4& Normal, float& IntersectionTime)
{
    const FPlane::FReal StartDist = FPlane(Normal).PlaneDot(Start);
    const FPlane::FReal EndDist = FPlane(Normal).PlaneDot(End);
 
    // Check if the line is completely on one side of the triangle, or if it's co-planar.
#if 1
    if ((StartDist == EndDist) || (StartDist < -0.001f && EndDist < -0.001f) || (StartDist > 0.001f && EndDist > 0.001f))
#else
    if ( (StartDist * EndDist) > -0.0001f )
#endif
    {
        return false;
    }
 
    // Figure out when it will hit the triangle
    float Time = float(-StartDist / (EndDist - StartDist)); // LWC_TODO: Precision loss
 
    // If this triangle is not closer than the previous hit, reject it
    if (Time < 0.f || Time >= IntersectionTime)
    {
        return false;
    }
 
    // Calculate the line's point of intersection with the node's plane
    const FVector4& Intersection = Start + Dir * Time;
    const FVector4* Verts[3] = 
    { 
        &V0, &V1, &V2
    };
 
    // Check if the point of intersection is inside the triangle's edges.
    for( int32 SideIndex = 0; SideIndex < 3; SideIndex++ )
    {
        const FVector4& SideDirection = Normal ^ (*Verts[(SideIndex + 1) % 3] - *Verts[SideIndex]);
        const FVector4::FReal SideW = Dot3(SideDirection, *Verts[SideIndex]);
        const FVector4::FReal DotW = Dot3(SideDirection, Intersection);
        if ((DotW - SideW) >= 0.001f)
        {
            return false;
        }
    }
    IntersectionTime = Time;
    return true;
}
 
static const VectorRegister GSmallNegativeNumber = DECLARE_VECTOR_REGISTER(-0.0001f, -0.0001f, -0.0001f, -0.0001f);
//extern const VectorRegister GSmallNegativeNumber;
 
static const VectorRegister GSmallNumber = DECLARE_VECTOR_REGISTER(0.0001f, 0.0001f, 0.0001f, 0.0001f);
//extern const VectorRegister GSmallNumber;
 
static const VectorRegister GZeroVectorRegister = DECLARE_VECTOR_REGISTER(0.0f, 0.0f, 0.0f, 0.0f);
 
static const VectorRegister VectorNegativeOne = MakeVectorRegister( -1.0f, -1.0f, -1.0f, -1.0f );
 
static int32 appLineCheckTriangleSOA(const FVector3SOA& Start, const FVector3SOA& End, const FVector3SOA& Dir, const FTriangleSOA& Triangle4, float& InOutIntersectionTime)
{
    VectorRegister TriangleMask;
 
    VectorRegister StartDist;
    StartDist = VectorMultiplyAdd( Triangle4.Normals.X, Start.X, Triangle4.Normals.W );
    StartDist = VectorMultiplyAdd( Triangle4.Normals.Y, Start.Y, StartDist );
    StartDist = VectorMultiplyAdd( Triangle4.Normals.Z, Start.Z, StartDist );
 
    VectorRegister EndDist;
    EndDist = VectorMultiplyAdd( Triangle4.Normals.X, End.X, Triangle4.Normals.W );
    EndDist = VectorMultiplyAdd( Triangle4.Normals.Y, End.Y, EndDist );
    EndDist = VectorMultiplyAdd( Triangle4.Normals.Z, End.Z, EndDist );
 
    // Are both end-points of the line on the same side of the triangle (or parallel to the triangle plane)?
    TriangleMask = VectorCompareLE(VectorMultiply(StartDist, EndDist), GSmallNegativeNumber);
    if ( VectorMaskBits(TriangleMask) == 0 )
    {
        return -1;
    }
 
    // Figure out when it will hit the triangle
    VectorRegister Time = VectorDivide( StartDist, VectorSubtract(StartDist, EndDist) );
 
    // If this triangle is not closer than the previous hit, reject it
    VectorRegister IntersectionTime = VectorLoadFloat1( &InOutIntersectionTime );
    TriangleMask = VectorBitwiseAnd( TriangleMask, VectorCompareGE( Time, VectorZero() ) );
    TriangleMask = VectorBitwiseAnd( TriangleMask, VectorCompareLT( Time, IntersectionTime ) );
    if ( VectorMaskBits(TriangleMask) == 0 )
    {
        return -1;
    }
 
    // Calculate the line's point of intersection with the node's plane
    const VectorRegister IntersectionX = VectorMultiplyAdd( Dir.X, Time, Start.X );
    const VectorRegister IntersectionY = VectorMultiplyAdd( Dir.Y, Time, Start.Y );
    const VectorRegister IntersectionZ = VectorMultiplyAdd( Dir.Z, Time, Start.Z );
 
    // Check if the point of intersection is inside the triangle's edges.
    for( int32 SideIndex = 0; SideIndex < 3; SideIndex++ )
    {
        const VectorRegister EdgeX = VectorSubtract( Triangle4.Positions[(SideIndex + 1) % 3].X, Triangle4.Positions[SideIndex].X );
        const VectorRegister EdgeY = VectorSubtract( Triangle4.Positions[(SideIndex + 1) % 3].Y, Triangle4.Positions[SideIndex].Y );
        const VectorRegister EdgeZ = VectorSubtract( Triangle4.Positions[(SideIndex + 1) % 3].Z, Triangle4.Positions[SideIndex].Z );
        const VectorRegister SideDirectionX = VectorNegateMultiplyAdd( Triangle4.Normals.Z, EdgeY, VectorMultiply(Triangle4.Normals.Y, EdgeZ) );
        const VectorRegister SideDirectionY = VectorNegateMultiplyAdd( Triangle4.Normals.X, EdgeZ, VectorMultiply(Triangle4.Normals.Z, EdgeX) );
        const VectorRegister SideDirectionZ = VectorNegateMultiplyAdd( Triangle4.Normals.Y, EdgeX, VectorMultiply(Triangle4.Normals.X, EdgeY) );
        VectorRegister SideW;
        SideW = VectorMultiply( SideDirectionX, Triangle4.Positions[SideIndex].X );
        SideW = VectorMultiplyAdd( SideDirectionY, Triangle4.Positions[SideIndex].Y, SideW );
        SideW = VectorMultiplyAdd( SideDirectionZ, Triangle4.Positions[SideIndex].Z, SideW );
        VectorRegister DotW;
        DotW = VectorMultiply( SideDirectionX, IntersectionX );
        DotW = VectorMultiplyAdd( SideDirectionY, IntersectionY, DotW );
        DotW = VectorMultiplyAdd( SideDirectionZ, IntersectionZ, DotW );
        TriangleMask = VectorBitwiseAnd( TriangleMask, VectorCompareLT( VectorSubtract(DotW, SideW), GSmallNumber ) );
        if ( VectorMaskBits(TriangleMask) == 0 )
        {
            return -1;
        }
    }
 
    // Set all non-hitting times to 1.0
    Time = VectorSelect( TriangleMask, Time, VectorOne() );
 
    // Get the best intersection time out of the 4 possibilities.
    VectorRegister BestTimes = VectorMin( Time, VectorSwizzle(Time, 2, 3, 0, 0) );
    BestTimes = VectorMin( BestTimes, VectorSwizzle(BestTimes, 1, 0, 0, 0) );
    IntersectionTime = VectorReplicate( BestTimes, 0 );
 
    // Get the triangle index that corresponds to the best time.
    // NOTE: This will pick the first triangle, in case there are multiple hits at the same spot.
    int32 SubIndex = VectorMaskBits( VectorCompareEQ( Time, IntersectionTime ) );
    SubIndex = appCountTrailingZeros( SubIndex );
 
    // Return results.
    VectorStoreFloat1( IntersectionTime, &InOutIntersectionTime );
    return SubIndex;
}
 
// This structure is used during the build process. It contains the triangle's
// centroid for calculating which plane it should be split or not with
template<typename KDOP_IDX_TYPE>
struct FkDOPBuildCollisionTriangle
{
    FVector4 V0;
    FVector4 V1;
    FVector4 V2;
 
    KDOP_IDX_TYPE MaterialIndex;
 
    inline FVector4 GetCentroid() const
    {
        return (V0 + V1 + V2) / 3.f;
    }
    FVector4 GetLocalNormal() const
    {
        FVector4 LocalNormal = ((V1 - V2) ^ (V0 - V2)).GetSafeNormal();
        LocalNormal.W = Dot3(V0, LocalNormal);
        return LocalNormal;
    }
 
    FkDOPBuildCollisionTriangle(
        KDOP_IDX_TYPE InMaterialIndex,
        const FVector4& vert0,const FVector4& vert1,const FVector4& vert2) :
        V0(vert0), V1(vert1), V2(vert2),
        MaterialIndex(InMaterialIndex)
    {
    }
};
 
// Forward declarations
template <typename COLL_DATA_PROVIDER,typename KDOP_IDX_TYPE> struct TkDOPNode;
template <typename COLL_DATA_PROVIDER,typename KDOP_IDX_TYPE> struct TkDOPTree;
template <typename COLL_DATA_PROVIDER,typename KDOP_IDX_TYPE> struct TkDOPLineCollisionCheck;
 
struct FFourBox
{
    MS_ALIGN(16) FVector4 Min[3]  GCC_ALIGN(16);
 
    FVector4 Max[3];
 
    void SetBox( int32 BoundingVolumeIndex, const FBox& Box )
    {
        using FVec4Real = decltype(FVector4::X);
        Min[0].Component(BoundingVolumeIndex) = (FVec4Real)Box.Min.X;
        Min[1].Component(BoundingVolumeIndex) = (FVec4Real)Box.Min.Y;
        Min[2].Component(BoundingVolumeIndex) = (FVec4Real)Box.Min.Z;
        Max[0].Component(BoundingVolumeIndex) = (FVec4Real)Box.Max.X;
        Max[1].Component(BoundingVolumeIndex) = (FVec4Real)Box.Max.Y;
        Max[2].Component(BoundingVolumeIndex) = (FVec4Real)Box.Max.Z;
    }
 
    FBox GetBox( int32 BoundingVolumeIndex )
    {
        FBox Box;
        Box.Min = FVector4(Min[0][BoundingVolumeIndex],Min[1][BoundingVolumeIndex],Min[2][BoundingVolumeIndex],1);
        Box.Max = FVector4(Max[0][BoundingVolumeIndex],Max[1][BoundingVolumeIndex],Max[2][BoundingVolumeIndex],1);
        return Box;
    }
};
 
#if PLATFORM_64BITS
    #define kDOPArray TArray
#else
    #define kDOPArray TChunkedArray
#endif
 
template <typename COLL_DATA_PROVIDER, typename KDOP_IDX_TYPE>
struct TkDOPNode
{
    typedef COLL_DATA_PROVIDER                          DataProviderType;
 
    typedef TkDOPNode<DataProviderType,KDOP_IDX_TYPE>   NodeType;
 
    FFourBox BoundingVolumes;
 
    // Note this isn't smaller since 4 byte alignment will take over anyway
    bool bIsLeaf;
    uint8 Occupancy;
 
    // Union of either child kDOP nodes or a list of enclosed triangles
    union
    {
        // This structure contains the left and right child kDOP indices
        // These index values correspond to the array in the FkDOPTree
        struct
        {
            KDOP_IDX_TYPE LeftNode;
            KDOP_IDX_TYPE RightNode;
        } n;
        // This structure contains the list of enclosed triangles
        // These index values correspond to the triangle information in the
        // FkDOPTree using the start and count as the means of delineating
        // which triangles are involved
        struct
        {
            KDOP_IDX_TYPE NumTriangles;
            KDOP_IDX_TYPE StartIndex;
        } t;
    };
 
    FORCEINLINE TkDOPNode()
    {
        n.LeftNode = ((KDOP_IDX_TYPE) -1);
        n.RightNode = ((KDOP_IDX_TYPE) -1);
    }
 
    FBox SplitTriangleList(int32 Start,int32 NumTris,
        TArray<FkDOPBuildCollisionTriangle<KDOP_IDX_TYPE> >& BuildTriangles,
        kDOPArray<FTriangleSOA>& SOATriangles,
        kDOPArray<NodeType>& Nodes)
    {
        // Figure out if we are a leaf node or not
        if (NumTris > 4)
        {
            // Still too many triangles, so continue subdividing the triangle list
            bIsLeaf = 0;
            Occupancy = 0;
            int32 BestPlane = -1;
            double BestMean = 0.f;
            double BestVariance = 0.f;
 
            // Determine how to split using the splatter algorithm
            {
                double Mean[NUM_PLANES] = { 0 };
                double Variance[NUM_PLANES] = { 0 };
 
                // Compute the mean for the triangle list
                for (int32 nTriangle = Start; nTriangle < Start + NumTris; nTriangle++)
                {
                    // Project the centroid of the triangle against the plane
                    // normals and accumulate to find the total projected
                    // weighting
                    FVector4 Centroid = BuildTriangles[nTriangle].GetCentroid();
 
                    for (int32 nPlane = 0; nPlane < NUM_PLANES; nPlane++)
                    {
                        Mean[nPlane] += Centroid[nPlane];
                    }
                }
 
                // Divide by the number of triangles to get the average
                for (int32 nPlane = 0; nPlane < NUM_PLANES; nPlane++)
                {
                    Mean[nPlane] /= NumTris;
                }
 
                // Compute variance of the triangle list
                for (int32 nTriangle = Start; nTriangle < Start + NumTris; nTriangle++)
                {
                    // Project the centroid again
                    FVector4 Centroid = BuildTriangles[nTriangle].GetCentroid();
 
                    // Now calculate the variance and accumulate it
                    for (int32 nPlane = 0; nPlane < NUM_PLANES; nPlane++)
                    {
                        Variance[nPlane] += (Centroid[nPlane] - Mean[nPlane]) * (Centroid[nPlane] - Mean[nPlane]);
                    }
                }
 
                // Determine which plane is the best to split on
                for (int32 nPlane = 0; nPlane < NUM_PLANES; nPlane++)
                {
                    // Get the average variance
                    Variance[nPlane] /= NumTris;
                    if (Variance[nPlane] >= BestVariance)
                    {
                        BestPlane = nPlane;
                        BestVariance = Variance[nPlane];
                        BestMean = Mean[nPlane];
                    }
                }
            }
 
            // Now that we have the plane to split on, work through the triangle
            // list placing them on the left or right of the splitting plane
            int32 Left = Start - 1;
            int32 Right = Start + NumTris;
            // Keep working through until the left index passes the right; we test that condition after each interior loop
            for (;;)
            {
                // Loop invariants: (1) Left < Right,
                // (2) All triangles <= Left belong on the left, all triangles >= Right belong on the right
                // (3) Left+1 is an untested triangle, Right-1 is an untested triangle
                FVector4::FReal Dot;
                // Increment Left until it points to triangle that belongs on the right, or Right==Left
                for (++Left; Left < Right; ++Left)
                {
                    Dot = BuildTriangles[Left].GetCentroid()[BestPlane];
                    if (Dot < BestMean)
                    {
                        break;
                    }
                }
                if (Left == Right)
                {
                    break;
                }
                // Decrement Right until it points to triangle that belongs on the left, or Right==Left
                for (--Right; Left < Right; --Right)
                {
                    Dot = BuildTriangles[Right].GetCentroid()[BestPlane];
                    if (Dot >= BestMean)
                    {
                        break;
                    }
                }
                if (Left == Right)
                {
                    break;
                }
                // Left points to a triangle that belongs on the Right; Right points to a triangle that belongs on the Left. Swap them.
                Swap(BuildTriangles[Left], BuildTriangles[Right]);
            }
            // After loop array is partitioned and Left is the first index that belongs on the right side of the plane.
            // Check for wacky degenerate case where more than GKDOPMaxTrisPerLeaf
            // fall all in the same kDOP
            if (Left == Start + NumTris || Right == Start)
            {
                Left = Start + (NumTris / 2);
            }
            // Add the two child nodes
            n.LeftNode = Nodes.AddZeroed(2);
            n.RightNode = n.LeftNode + 1;
            // Have the left node recursively subdivide it's list and set bounding volume.
            FBox LeftBoundingVolume = Nodes[n.LeftNode].SplitTriangleList(Start,Left - Start,BuildTriangles,SOATriangles,Nodes);
            BoundingVolumes.SetBox(0,LeftBoundingVolume);
            // Set unused index 2,3 to child nodes of left node.
            BoundingVolumes.SetBox(2,Nodes[n.LeftNode].BoundingVolumes.GetBox(0));
            BoundingVolumes.SetBox(3,Nodes[n.LeftNode].BoundingVolumes.GetBox(1));
 
            // And now have the right node recursively subdivide it's list and set bounding volume.         
            FBox RightBoundingVolume = Nodes[n.RightNode].SplitTriangleList(Left,Start + NumTris - Left,BuildTriangles,SOATriangles,Nodes);
            BoundingVolumes.SetBox(1,RightBoundingVolume);
 
            // Non-leaf node bounds are the "sum" of the left and right nodes' volumes.
            return LeftBoundingVolume + RightBoundingVolume;
        }
        else
        {
            // Build SOA triangles
 
            // "NULL triangle", used when a leaf can't fill all 4 triangles in a FTriangleSOA.
            // No line should ever hit these triangles, set the values so that it can never happen.
            FkDOPBuildCollisionTriangle<KDOP_IDX_TYPE> EmptyTriangle(0,FVector4(0,0,0,0),FVector4(0,0,0,0),FVector4(0,0,0,0));
            
            t.StartIndex = SOATriangles.Num();
            t.NumTriangles = Align<int32>(NumTris, 4) / 4;
            SOATriangles.AddZeroed( t.NumTriangles );
 
            int32 BuildTriIndex = Start;
            for ( uint32 SOAIndex=0; SOAIndex < t.NumTriangles; ++SOAIndex )
            {
                FkDOPBuildCollisionTriangle<KDOP_IDX_TYPE>* Tris[4] = { &EmptyTriangle, &EmptyTriangle, &EmptyTriangle, &EmptyTriangle };
                FTriangleSOA& SOA = SOATriangles[t.StartIndex + SOAIndex];
                int32 SubIndex = 0;
                for ( ; SubIndex < 4 && BuildTriIndex < (Start+NumTris); ++SubIndex, ++BuildTriIndex )
                {
                    Tris[SubIndex] = &BuildTriangles[BuildTriIndex];
                    SOA.Payload[SubIndex] = Tris[SubIndex]->MaterialIndex;
                }
                for ( ; SubIndex < 4; ++SubIndex )
                {
                    SOA.Payload[SubIndex] = 0xffffffff;
                }
 
                SOA.Positions[0].X = VectorSet( Tris[0]->V0.X, Tris[1]->V0.X, Tris[2]->V0.X, Tris[3]->V0.X );
                SOA.Positions[0].Y = VectorSet( Tris[0]->V0.Y, Tris[1]->V0.Y, Tris[2]->V0.Y, Tris[3]->V0.Y );
                SOA.Positions[0].Z = VectorSet( Tris[0]->V0.Z, Tris[1]->V0.Z, Tris[2]->V0.Z, Tris[3]->V0.Z );
                SOA.Positions[1].X = VectorSet( Tris[0]->V1.X, Tris[1]->V1.X, Tris[2]->V1.X, Tris[3]->V1.X );
                SOA.Positions[1].Y = VectorSet( Tris[0]->V1.Y, Tris[1]->V1.Y, Tris[2]->V1.Y, Tris[3]->V1.Y );
                SOA.Positions[1].Z = VectorSet( Tris[0]->V1.Z, Tris[1]->V1.Z, Tris[2]->V1.Z, Tris[3]->V1.Z );
                SOA.Positions[2].X = VectorSet( Tris[0]->V2.X, Tris[1]->V2.X, Tris[2]->V2.X, Tris[3]->V2.X );
                SOA.Positions[2].Y = VectorSet( Tris[0]->V2.Y, Tris[1]->V2.Y, Tris[2]->V2.Y, Tris[3]->V2.Y );
                SOA.Positions[2].Z = VectorSet( Tris[0]->V2.Z, Tris[1]->V2.Z, Tris[2]->V2.Z, Tris[3]->V2.Z );
 
                const FVector4& Tris0LocalNormal = Tris[0]->GetLocalNormal();
                const FVector4& Tris1LocalNormal = Tris[1]->GetLocalNormal();
                const FVector4& Tris2LocalNormal = Tris[2]->GetLocalNormal();
                const FVector4& Tris3LocalNormal = Tris[3]->GetLocalNormal();
 
                SOA.Normals.X = VectorSet( Tris0LocalNormal.X, Tris1LocalNormal.X, Tris2LocalNormal.X, Tris3LocalNormal.X );
                SOA.Normals.Y = VectorSet( Tris0LocalNormal.Y, Tris1LocalNormal.Y, Tris2LocalNormal.Y, Tris3LocalNormal.Y );
                SOA.Normals.Z = VectorSet( Tris0LocalNormal.Z, Tris1LocalNormal.Z, Tris2LocalNormal.Z, Tris3LocalNormal.Z );
                SOA.Normals.W = VectorSet( -Tris0LocalNormal.W, -Tris1LocalNormal.W, -Tris2LocalNormal.W, -Tris3LocalNormal.W );
            }
 
            // No need to subdivide further so make this a leaf node
            bIsLeaf = 1;
 
            check(NumTris <= std::numeric_limits<uint8>::max());
            Occupancy = static_cast<uint8>(NumTris);
            
            // Generate bounding volume for leaf which is passed up the call chain.
            FBox BoundingVolume(ForceInit);
            for (int32 TriangleIndex=Start; TriangleIndex<Start + NumTris; TriangleIndex++)
            {
                BoundingVolume += FVector(BuildTriangles[TriangleIndex].V0);
                BoundingVolume += FVector(BuildTriangles[TriangleIndex].V1);
                BoundingVolume += FVector(BuildTriangles[TriangleIndex].V2);
            }
            BoundingVolumes.SetBox(0,BoundingVolume);
            BoundingVolumes.SetBox(1,BoundingVolume);
            BoundingVolumes.SetBox(2,BoundingVolume);
            BoundingVolumes.SetBox(3,BoundingVolume);
 
            return BoundingVolume;
        }
    }
 
    FORCEINLINE void LineCheckBounds(TkDOPLineCollisionCheck<COLL_DATA_PROVIDER,KDOP_IDX_TYPE>& Check, FVector4& HitTime, int32 NodeHit[4] ) const
    {
#define PLAIN_C 0
#if PLAIN_C
        for( int32 BoxIndex=0; BoxIndex<4; BoxIndex++ )
        {
            // 0: Create constants
            FVector4 BoxMin( BoundingVolumes.Min[0][BoxIndex], BoundingVolumes.Min[1][BoxIndex], BoundingVolumes.Min[2][BoxIndex], 0 );
            FVector4 BoxMax( BoundingVolumes.Max[0][BoxIndex], BoundingVolumes.Max[1][BoxIndex], BoundingVolumes.Max[2][BoxIndex], 0 );
 
            // 1: Calculate slabs.
            FVector4 Slab1 = (BoxMin - Check.LocalStart) * Check.LocalOneOverDir;
            FVector4 Slab2 = (BoxMax - Check.LocalStart) * Check.LocalOneOverDir;
 
            // 2: Figure out per component min/ max
            FVector4 SlabMin = FVector4( FMath::Min(Slab1.X, Slab2.X), FMath::Min(Slab1.Y, Slab2.Y), FMath::Min(Slab1.Z, Slab2.Z), FMath::Min(Slab1.W, Slab2.W) );
            FVector4 SlabMax = FVector4( FMath::Max(Slab1.X, Slab2.X), FMath::Max(Slab1.Y, Slab2.Y), FMath::Max(Slab1.Z, Slab2.Z), FMath::Max(Slab1.W, Slab2.W) );
 
            // 3: Figure out global min/ max
            float MinTime = Max3( SlabMin.X, SlabMin.Y, SlabMin.Z );
            float MaxTime = Min3( SlabMax.X, SlabMax.Y, SlabMax.Z );
 
            // 4: Calculate hit time and determine whether there was a hit.
            HitTime[BoxIndex] = MinTime;            
            NodeHit[BoxIndex] = (MaxTime >= 0 && MaxTime >= MinTime && MinTime < Check.Result->Time) ? 0xFFFFFFFF : 0;
        }
#else
        // 0: load everything into registers
        const VectorRegister OriginX        = VectorSetFloat1( Check.LocalStart.X );
        const VectorRegister OriginY        = VectorSetFloat1( Check.LocalStart.Y );
        const VectorRegister OriginZ        = VectorSetFloat1( Check.LocalStart.Z );
        const VectorRegister InvDirX        = VectorSetFloat1( Check.LocalOneOverDir.X );
        const VectorRegister InvDirY        = VectorSetFloat1( Check.LocalOneOverDir.Y );
        const VectorRegister InvDirZ        = VectorSetFloat1( Check.LocalOneOverDir.Z );
        const VectorRegister CurrentHitTime = VectorSetFloat1( Check.Result->Time );
        // Boxes are FVector2D so we need to unshuffle the data.
        const VectorRegister BoxMinX        = VectorLoadAligned( &BoundingVolumes.Min[0] );
        const VectorRegister BoxMinY        = VectorLoadAligned( &BoundingVolumes.Min[1] );
        const VectorRegister BoxMinZ        = VectorLoadAligned( &BoundingVolumes.Min[2] );
        const VectorRegister BoxMaxX        = VectorLoadAligned( &BoundingVolumes.Max[0] );
        const VectorRegister BoxMaxY        = VectorLoadAligned( &BoundingVolumes.Max[1] );
        const VectorRegister BoxMaxZ        = VectorLoadAligned( &BoundingVolumes.Max[2] );
 
        // 1: Calculate slabs.
        const VectorRegister BoxMinSlabX    = VectorMultiply( VectorSubtract( BoxMinX, OriginX ), InvDirX );
        const VectorRegister BoxMinSlabY    = VectorMultiply( VectorSubtract( BoxMinY, OriginY ), InvDirY );
        const VectorRegister BoxMinSlabZ    = VectorMultiply( VectorSubtract( BoxMinZ, OriginZ ), InvDirZ );        
        const VectorRegister BoxMaxSlabX    = VectorMultiply( VectorSubtract( BoxMaxX, OriginX ), InvDirX );
        const VectorRegister BoxMaxSlabY    = VectorMultiply( VectorSubtract( BoxMaxY, OriginY ), InvDirY );
        const VectorRegister BoxMaxSlabZ    = VectorMultiply( VectorSubtract( BoxMaxZ, OriginZ ), InvDirZ );
 
        // 2: Figure out per component min/ max
        const VectorRegister SlabMinX       = VectorMin( BoxMinSlabX, BoxMaxSlabX );
        const VectorRegister SlabMinY       = VectorMin( BoxMinSlabY, BoxMaxSlabY );
        const VectorRegister SlabMinZ       = VectorMin( BoxMinSlabZ, BoxMaxSlabZ );
        const VectorRegister SlabMaxX       = VectorMax( BoxMinSlabX, BoxMaxSlabX );
        const VectorRegister SlabMaxY       = VectorMax( BoxMinSlabY, BoxMaxSlabY );
        const VectorRegister SlabMaxZ       = VectorMax( BoxMinSlabZ, BoxMaxSlabZ );
        
        // 3: Figure out global min/ max
        const VectorRegister SlabMinXY      = VectorMax( SlabMinX , SlabMinY );
        const VectorRegister MinTime        = VectorMax( SlabMinXY, SlabMinZ );
        const VectorRegister SlabMaxXY      = VectorMin( SlabMaxX , SlabMaxY );
        const VectorRegister MaxTime        = VectorMin( SlabMaxXY, SlabMaxZ );
 
        // 4: Calculate hit time and determine whether there was a hit.     
        VectorStoreAligned( MinTime, &HitTime );
        const VectorRegister OutNodeHit     = VectorBitwiseAnd( VectorCompareGE( MaxTime, VectorZero() ), VectorCompareGE( MaxTime, MinTime ) );
        const VectorRegister CloserNodeHit  = VectorBitwiseAnd( OutNodeHit, VectorCompareGT( CurrentHitTime, MinTime ) );
        VectorStoreAligned( CloserNodeHit, (float*) NodeHit );
#endif
    }
 
    bool LineCheck(TkDOPLineCollisionCheck<COLL_DATA_PROVIDER,KDOP_IDX_TYPE>& Check, TTraversalHistory<KDOP_IDX_TYPE> History) const
    {
        bool bHit = 0;
        // If this is a node, check the two child nodes and pick the closest one
        // to recursively check against and only check the second one if there is
        // not a hit or the hit returned is further out than the second node
        if (bIsLeaf == 0)
        {
            // Check both left and right node at the same time.
            FVector4 NodeHitTime;
            MS_ALIGN(16) int32  NodeHit[4] GCC_ALIGN(16);
            LineCheckBounds( Check, NodeHitTime, NodeHit );
 
            // Left node was hit.
            if( NodeHit[0] )
            {
                // Left and Right node are hit.
                if( NodeHit[1] )
                {
                    // Left node is closer than right node.
                    if( NodeHitTime.X < NodeHitTime.Y )
                    {
                        bHit = Check.Nodes[n.LeftNode].LineCheckPreCalculated(Check,NodeHitTime,History.AddNode(n.LeftNode),NodeHit);
                        // Only check right node if it could possibly be a closer hit
                        if( NodeHitTime.Y < Check.Result->Time
                        // No need to check if we have a hit and don't care about closest
                        &&  (!bHit || Check.bFindClosestIntersection))
                        {
                            bHit |= Check.Nodes[n.RightNode].LineCheck(Check,History.AddNode(n.RightNode));
                        }
                    }
                    // Right node is closer than left node.
                    else
                    {
                        bHit = Check.Nodes[n.RightNode].LineCheck(Check,History.AddNode(n.RightNode));
                        // Only check left node if it could possibly be a closer hit
                        if( NodeHitTime.X < Check.Result->Time
                        // No need to check if we have a hit and don't care about closest
                        &&  (!bHit || Check.bFindClosestIntersection))
                        {
                            bHit |= Check.Nodes[n.LeftNode].LineCheckPreCalculated(Check,NodeHitTime,History.AddNode(n.LeftNode),NodeHit);
                        }
                    }
                }
                // Only left node was hit.
                else
                {
                    bHit = Check.Nodes[n.LeftNode].LineCheckPreCalculated(Check,NodeHitTime,History.AddNode(n.LeftNode),NodeHit);
                }
            }
            // Left node was not hit.
            else
            {
                // Only right node was hit.
                if( NodeHit[1] )
                {           
                    bHit = Check.Nodes[n.RightNode].LineCheck(Check,History.AddNode(n.RightNode));                  
                }
                // No node was hit.
                else
                {
                    return false;
                }
            }
        }
        else
        {
            // This is a leaf, check the triangles for a hit
            bHit = LineCheckTriangles(Check,History);
        }
        return bHit;
    }
 
    bool LineCheckPreCalculated(TkDOPLineCollisionCheck<COLL_DATA_PROVIDER,KDOP_IDX_TYPE>& Check, const FVector4& NodeHitTime, TTraversalHistory<KDOP_IDX_TYPE> History, int32* NodeHit) const
    {
        bool bHit = 0;
        // If this is a node, check the two child nodes and pick the closest one
        // to recursively check against and only check the second one if there is
        // not a hit or the hit returned is further out than the second node
        if (bIsLeaf == 0)
        {
            // Left node was hit.
            if( NodeHit[2] )
            {
                // Left and Right node are hit.
                if( NodeHit[3] )
                {
                    // Left node is closer than right node.
                    if( NodeHitTime.Z < NodeHitTime.W )
                    {
                        bHit = Check.Nodes[n.LeftNode].LineCheck(Check,History.AddNode(n.LeftNode));
                        // Only check right node if it could possibly be a closer hit
                        if( NodeHitTime.W < Check.Result->Time
                        // No need to check if we have a hit and don't care about closest
                        &&  (!bHit || Check.bFindClosestIntersection))
                        {
                            bHit |= Check.Nodes[n.RightNode].LineCheck(Check,History.AddNode(n.RightNode));
                        }
                    }
                    // Right node is closer than left node.
                    else
                    {
                        bHit = Check.Nodes[n.RightNode].LineCheck(Check,History.AddNode(n.RightNode));
                        // Only check left node if it could possibly be a closer hit
                        if( NodeHitTime.Z < Check.Result->Time
                        // No need to check if we have a hit and don't care about closest
                        &&  (!bHit || Check.bFindClosestIntersection))
                        {
                            bHit |= Check.Nodes[n.LeftNode].LineCheck(Check,History.AddNode(n.LeftNode));
                        }
                    }
                }
                // Only left node was hit.
                else
                {
                    bHit = Check.Nodes[n.LeftNode].LineCheck(Check,History.AddNode(n.LeftNode));
                }
            }
            // Left node was not hit.
            else
            {
                // Only right node was hit.
                if( NodeHit[3] )
                {           
                    bHit = Check.Nodes[n.RightNode].LineCheck(Check,History.AddNode(n.RightNode));                  
                }
                // No node was hit.
                else
                {
                    return false;
                }
            }
        }
        else
        {
            // This is a leaf, check the triangles for a hit
            bHit = LineCheckTriangles(Check,History);
        }
        return bHit;
    }
 
    bool LineCheckTriangles(TkDOPLineCollisionCheck<COLL_DATA_PROVIDER,KDOP_IDX_TYPE>& Check, const TTraversalHistory<KDOP_IDX_TYPE>& History) const
    {
        // Assume a miss
        bool bHit = false;
        for ( KDOP_IDX_TYPE SOAIndex = t.StartIndex; SOAIndex < (t.StartIndex + t.NumTriangles); SOAIndex++ )
        {
            const FTriangleSOA& TriangleSOA = Check.SOATriangles[SOAIndex];
            int32 SubIndex = appLineCheckTriangleSOA( Check.StartSOA, Check.EndSOA, Check.DirSOA, TriangleSOA, Check.Result->Time );
            if ( SubIndex >= 0 )
            {
                bHit = true;
                Check.LocalHitNormal.X = (decltype(FVector4::X))VectorGetComponentDynamic(TriangleSOA.Normals.X, SubIndex);
                Check.LocalHitNormal.Y = (decltype(FVector4::Y))VectorGetComponentDynamic(TriangleSOA.Normals.Y, SubIndex);
                Check.LocalHitNormal.Z = (decltype(FVector4::X))VectorGetComponentDynamic(TriangleSOA.Normals.Z, SubIndex);
                Check.Result->Item = TriangleSOA.Payload[SubIndex];
                Check.HitNodeIndex = History.GetOldestNode();
 
                // Early out if we don't care about the closest intersection.
                if( !Check.bFindClosestIntersection )
                {
                    break;
                }
            }
        }
        return bHit;
    }
};
 
template<typename COLL_DATA_PROVIDER, typename KDOP_IDX_TYPE>
struct TkDOPTree
{
    typedef COLL_DATA_PROVIDER                          DataProviderType;
 
    typedef TkDOPNode<DataProviderType,KDOP_IDX_TYPE>   NodeType;
 
    kDOPArray<NodeType> Nodes;
 
    kDOPArray<FTriangleSOA> SOATriangles;
 
    void Build(TArray<FkDOPBuildCollisionTriangle<KDOP_IDX_TYPE> >& BuildTriangles)
    {
        float kDOPBuildTime = 0;
        {
            // Empty the current set of nodes and preallocate the memory so it doesn't
            // reallocate memory while we are recursively walking the tree
            // With near-perfect packing, we could easily size these to be
            // Nodes = (n / 2) + 1 and SOATriangles = (n / 4) + 1
            Nodes.Empty(BuildTriangles.Num());
            SOATriangles.Empty(BuildTriangles.Num());
 
            // Add the root node
            Nodes.AddZeroed();
 
            // Now tell that node to recursively subdivide the entire set of triangles
            Nodes[0].SplitTriangleList(0,BuildTriangles.Num(),BuildTriangles,SOATriangles,Nodes);
 
            // Don't waste memory.
            Nodes.Shrink();
            SOATriangles.Shrink();
        }
    }
 
    bool LineCheck(TkDOPLineCollisionCheck<COLL_DATA_PROVIDER,KDOP_IDX_TYPE>& Check) const
    {
        // Recursively check for a hit
        TTraversalHistory<KDOP_IDX_TYPE> History;
        bool bHit = Nodes[0].LineCheck(Check, History.AddNode(0));
        return bHit;
    }
};
 
template <typename COLL_DATA_PROVIDER, typename KDOP_IDX_TYPE> struct TkDOPCollisionCheck
{
    typedef COLL_DATA_PROVIDER DataProviderType;
 
    typedef TkDOPNode<DataProviderType,KDOP_IDX_TYPE> NodeType;
 
    typedef TkDOPTree<DataProviderType,KDOP_IDX_TYPE> TreeType;
 
    const DataProviderType& CollDataProvider;
    const TreeType& kDOPTree;
    const kDOPArray<NodeType>& Nodes;
    const kDOPArray<FTriangleSOA>& SOATriangles;
 
    TkDOPCollisionCheck(const DataProviderType& InCollDataProvider) :
        CollDataProvider(InCollDataProvider),
        kDOPTree(CollDataProvider.GetkDOPTree()),
        Nodes(kDOPTree.Nodes),
        SOATriangles(kDOPTree.SOATriangles)
    {
    }
};
 
template <typename COLL_DATA_PROVIDER, typename KDOP_IDX_TYPE> struct TkDOPLineCollisionCheck :
    public TkDOPCollisionCheck<COLL_DATA_PROVIDER,KDOP_IDX_TYPE>
{
    FkHitResult* Result;
    // Constant input vars
    const FVector4& Start;
    const FVector4& End;
 
    const bool bFindClosestIntersection;
    // Locally calculated vectors
    FVector4 LocalStart;
    FVector4 LocalEnd;
    FVector4 LocalDir;
    FVector4 LocalOneOverDir;
    // Normal in local space which gets transformed to world at the very end
    FVector4 LocalHitNormal;
 
    KDOP_IDX_TYPE HitNodeIndex;
    
    FVector3SOA StartSOA;
    FVector3SOA EndSOA;
    FVector3SOA DirSOA;
 
    TkDOPLineCollisionCheck(const FVector4& InStart,const FVector4& InEnd,
        bool bInbFindClosestIntersection,
        const COLL_DATA_PROVIDER& InCollDataProvider,
        FkHitResult* InResult) 
        :
        TkDOPCollisionCheck<COLL_DATA_PROVIDER,KDOP_IDX_TYPE>(InCollDataProvider),
        Result(InResult), 
        Start(InStart), 
        End(InEnd), 
        bFindClosestIntersection(bInbFindClosestIntersection), 
        HitNodeIndex(0xFFFFFFFF)
    {
        const FMatrix& WorldToLocal = TkDOPCollisionCheck<COLL_DATA_PROVIDER,KDOP_IDX_TYPE>::CollDataProvider.GetWorldToLocal();
        // Move start and end to local space
        LocalStart = WorldToLocal.TransformPosition(Start);
        LocalEnd = WorldToLocal.TransformPosition(End);
        // Calculate the vector's direction in local space
        LocalDir = LocalEnd - LocalStart;
        // Build the one over dir
        LocalOneOverDir.X = LocalDir.X ? 1.f / LocalDir.X : MAX_FLT;
        LocalOneOverDir.Y = LocalDir.Y ? 1.f / LocalDir.Y : MAX_FLT;
        LocalOneOverDir.Z = LocalDir.Z ? 1.f / LocalDir.Z : MAX_FLT;
 
        // Construct the SOA data
        StartSOA.X = VectorLoadFloat1( &LocalStart.X );
        StartSOA.Y = VectorLoadFloat1( &LocalStart.Y );
        StartSOA.Z = VectorLoadFloat1( &LocalStart.Z );
        EndSOA.X = VectorLoadFloat1( &LocalEnd.X );
        EndSOA.Y = VectorLoadFloat1( &LocalEnd.Y );
        EndSOA.Z = VectorLoadFloat1( &LocalEnd.Z );
        DirSOA.X = VectorLoadFloat1( &LocalDir.X );
        DirSOA.Y = VectorLoadFloat1( &LocalDir.Y );
        DirSOA.Z = VectorLoadFloat1( &LocalDir.Z );
    }
 
    FORCEINLINE FVector4 GetHitNormal(void)
    {
        // Transform the hit back into world space using the transpose adjoint
        FVector4 Normal = TkDOPCollisionCheck<COLL_DATA_PROVIDER,KDOP_IDX_TYPE>::CollDataProvider.GetLocalToWorldTransposeAdjoint().TransformVector(LocalHitNormal).GetSafeNormal();
        // Flip the normal if the triangle is inverted
        if (TkDOPCollisionCheck<COLL_DATA_PROVIDER,KDOP_IDX_TYPE>::CollDataProvider.GetDeterminant() < 0.f)
        {
            Normal = -Normal;
        }
        return Normal;
    }
};