TetUtil.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "VectorTypes.h"
#include "TriangleTypes.h"
#include "CompGeom/ExactPredicates.h"
 
namespace UE::Geometry::TetUtil
{
    // Fill an array with the oriented triangle faces of the tet
    template<bool bReverseOrientation = false>
    void GetTetFaces(const FIndex4i& Tet, FIndex3i OutFaces[4])
    {
        const FIndex3i* FaceOrdering = GetTetFaceOrdering<bReverseOrientation>();
        OutFaces[0] = FIndex3i(Tet[FaceOrdering[0].A], Tet[FaceOrdering[0].B], Tet[FaceOrdering[0].C]);
        OutFaces[1] = FIndex3i(Tet[FaceOrdering[1].A], Tet[FaceOrdering[1].B], Tet[FaceOrdering[1].C]);
        OutFaces[2] = FIndex3i(Tet[FaceOrdering[2].A], Tet[FaceOrdering[2].B], Tet[FaceOrdering[2].C]);
        OutFaces[3] = FIndex3i(Tet[FaceOrdering[3].A], Tet[FaceOrdering[3].B], Tet[FaceOrdering[3].C]);
    }
 
    // Test whether point Pt is inside or on a (non-degenerate) tetrahedron Tet.
    // Note: Will always report 'outside' for a fully degenerate (flat) tetrahedron
    // @return 0 if Pt is outside Tet (or Tet is degenerate), 1 if Pt is inside a positively-oriented Tet, -1 if Pt is inside and Tet is inverted
    template<typename RealType>
    int32 IsInsideExact(const TTetrahedron3<RealType>& Tet, TVector<RealType>& Pt)
    {
        int32 SeenSide = 0;
        for (int32 TetFace = 0; TetFace < 4; ++TetFace)
        {
            FIndex3i FaceInds = Tet.GetFaceIndices(TetFace);
            int32 Side = TMathUtil<RealType>::SignAsInt(ExactPredicates::Orient3<RealType>(Tet.V[FaceInds.A], Tet.V[FaceInds.B], Tet.V[FaceInds.C], Pt));
            if (Side != 0)
            {
                if (Side * SeenSide < 0)
                {
                    return 0;
                }
                SeenSide = Side;
            }
        }
        
        return SeenSide;
    }
 
} // end namespace UE::Geometry::TetUtil