face.C

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  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
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    Copyright (C) 2011-2016 OpenFOAM Foundation
    Copyright (C) 2021-2025 OpenCFD Ltd.
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License
    This file is part of OpenFOAM.
 
    OpenFOAM is free software: you can redistribute it and/or modify it
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    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.
 
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    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
    for more details.
 
    You should have received a copy of the GNU General Public License
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#include "face.H"
#include "triFace.H"
#include "triangle.H"
#include "mathematicalConstants.H"
#include "Circulator.H"
 
// * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //
 
const char* const Foam::face::typeName = "face";
 
 
// * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
 
Foam::tmp<Foam::vectorField>
Foam::face::calcEdgeVectors(const UList<point>& points) const
{
    auto tedgeVecs = tmp<vectorField>::New(size());
    auto& edgeVecs = tedgeVecs.ref();
 
    forAll(edgeVecs, i)
    {
        edgeVecs[i] = vector(points[nextLabel(i)] - points[thisLabel(i)]);
        edgeVecs[i].normalise();
    }
 
    return tedgeVecs;
}
 
 
Foam::label Foam::face::mostConcaveAngle
(
    const UList<point>& points,
    const vectorField& edges,
    scalar& maxAngle
) const
{
    vector n(areaNormal(points));
 
    label index = 0;
    maxAngle = -GREAT;
 
    forAll(edges, i)
    {
        const vector& leftEdge = edges[rcIndex(i)];
        const vector& rightEdge = edges[i];
 
        vector edgeNormal = (rightEdge ^ leftEdge);
 
        // NOTE: is -ve angle since left edge pointing in other direction
        scalar edgeCos = (leftEdge & rightEdge);
        scalar edgeAngle = acos(clamp(edgeCos, -1, 1));
 
        scalar angle;
 
        if ((edgeNormal & n) > 0)
        {
            // Concave angle.
            angle = constant::mathematical::pi + edgeAngle;
        }
        else
        {
            // Convex angle. Note '-' to take into account that rightEdge
            // and leftEdge are head-to-tail connected.
            angle = constant::mathematical::pi - edgeAngle;
        }
 
        if (maxAngle < angle)
        {
            maxAngle = angle;
            index = i;
        }
    }
 
    return index;
}
 
 
Foam::label Foam::face::split
(
    const face::splitMode mode,
    const UList<point>& points,
    label& triI,
    label& quadI,
    faceList& triFaces,
    faceList& quadFaces
) const
{
    const label oldIndices = (triI + quadI);
 
    if (size() < 3)
    {
        FatalErrorInFunction
            << "Serious problem: asked to split a face with < 3 vertices"
            << abort(FatalError);
    }
    else if (size() == 3)
    {
        // Triangle. Just copy.
        if (mode == COUNTTRIANGLE || mode == COUNTQUAD)
        {
            triI++;
        }
        else
        {
            triFaces[triI++] = *this;
        }
    }
    else if (size() == 4)
    {
        if (mode == COUNTTRIANGLE)
        {
            triI += 2;
        }
        if (mode == COUNTQUAD)
        {
            quadI++;
        }
        else if (mode == SPLITTRIANGLE)
        {
            //  Start at point with largest internal angle.
            const vectorField edges(calcEdgeVectors(points));
 
            scalar minAngle;
            label startIndex = mostConcaveAngle(points, edges, minAngle);
 
            label nextIndex = fcIndex(startIndex);
            label splitIndex = fcIndex(nextIndex);
 
            // Create triangles
            face triFace(3);
            triFace[0] = operator[](startIndex);
            triFace[1] = operator[](nextIndex);
            triFace[2] = operator[](splitIndex);
 
            triFaces[triI++] = triFace;
 
            triFace[0] = operator[](splitIndex);
            triFace[1] = operator[](fcIndex(splitIndex));
            triFace[2] = operator[](startIndex);
 
            triFaces[triI++] = triFace;
        }
        else
        {
            quadFaces[quadI++] = *this;
        }
    }
    else
    {
        // General case. Like quad: search for largest internal angle.
 
        const vectorField edges(calcEdgeVectors(points));
 
        scalar minAngle = 1;
        label startIndex = mostConcaveAngle(points, edges, minAngle);
 
        scalar bisectAngle = minAngle/2;
        const vector& rightEdge = edges[startIndex];
 
        //
        // Look for opposite point which as close as possible bisects angle
        //
 
        // split candidate starts two points away.
        label index = fcIndex(fcIndex(startIndex));
 
        label minIndex = index;
        scalar minDiff = constant::mathematical::pi;
 
        for (label i = 0; i < size() - 3; i++)
        {
            vector splitEdge
            (
                points[operator[](index)]
              - points[operator[](startIndex)]
            );
            splitEdge.normalise();
 
            const scalar splitCos = splitEdge & rightEdge;
            const scalar splitAngle = acos(clamp(splitCos, -1, 1));
            const scalar angleDiff = fabs(splitAngle - bisectAngle);
 
            if (angleDiff < minDiff)
            {
                minDiff = angleDiff;
                minIndex = index;
            }
 
            // Go to next candidate
            index = fcIndex(index);
        }
 
 
        // Split into two subshapes.
        //     face1: startIndex to minIndex
        //     face2: minIndex to startIndex
 
        // Get sizes of the two subshapes
        label diff = 0;
        if (minIndex > startIndex)
        {
            diff = minIndex - startIndex;
        }
        else
        {
            // Folded around
            diff = minIndex + size() - startIndex;
        }
 
        label nPoints1 = diff + 1;
        label nPoints2 = size() - diff + 1;
 
        // Collect face1 points
        face face1(nPoints1);
 
        index = startIndex;
        for (label i = 0; i < nPoints1; i++)
        {
            face1[i] = operator[](index);
            index = fcIndex(index);
        }
 
        // Collect face2 points
        face face2(nPoints2);
 
        index = minIndex;
        for (label i = 0; i < nPoints2; i++)
        {
            face2[i] = operator[](index);
            index = fcIndex(index);
        }
 
        // Split faces
        face1.split(mode, points, triI, quadI, triFaces, quadFaces);
        face2.split(mode, points, triI, quadI, triFaces, quadFaces);
    }
 
    return (triI + quadI - oldIndices);
}
 
 
// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
Foam::face::face(const triFace& f)
:
    labelList(f)
{}
 
 
// * * * * * * * * * * * * * Static Member Functions * * * * * * * * * * * * //
 
int Foam::face::compare(const face& a, const face& b)
{
    // Basic rule: we assume that the sequence of labels in each list
    // will be circular in the same order (but not necessarily in the
    // same direction or from the same starting point).
 
    const label sizeA = a.size();
    const label sizeB = b.size();
 
    if (sizeA != sizeB)
    {
        // Trivial reject: faces have different sizes
        return 0;
    }
    else if (sizeA == 0)
    {
        // Both faces with zero vertices. Always identical
        return 1;
    }
    else if (sizeA == 1)
    {
        // Both faces with a single vertex. Simple check
        return (a[0] == b[0] ? 1 : 0);
    }
 
    ConstCirculator<face> aCirc(a);
    ConstCirculator<face> bCirc(b);
 
    // Rotate face b until its element matches the starting element of face a.
    do
    {
        if (aCirc() == bCirc())
        {
            // Set bCirc fulcrum to its iterator and increment the iterators
            bCirc.setFulcrumToIterator();
            ++aCirc;
            ++bCirc;
 
            break;
        }
    } while (bCirc.circulate(CirculatorBase::CLOCKWISE));
 
    // If the circulator has stopped then faces a and b do not share a matching
    // point. Doesn't work on matching, single element face.
    if (!bCirc.circulate())
    {
        return 0;
    }
 
    // Look forwards around the faces for a match
    do
    {
        if (*aCirc != *bCirc)
        {
            break;
        }
    }
    while
    (
        aCirc.circulate(CirculatorBase::CLOCKWISE),
        bCirc.circulate(CirculatorBase::CLOCKWISE)
    );
 
    // If the circulator has stopped then faces a and b matched.
    if (!aCirc.circulate())
    {
        return 1;
    }
    else
    {
        // Reset the circulators back to their fulcrum
        aCirc.setIteratorToFulcrum();
        bCirc.setIteratorToFulcrum();
        ++aCirc;
        --bCirc;
    }
 
    // Look backwards around the faces for a match
    do
    {
        if (*aCirc != *bCirc)
        {
            break;
        }
    }
    while
    (
        aCirc.circulate(CirculatorBase::CLOCKWISE),
        bCirc.circulate(CirculatorBase::ANTICLOCKWISE)
    );
 
    // If the circulator has stopped then faces a and b matched.
    if (!aCirc.circulate())
    {
        return -1;
    }
 
    return 0;
}
 
 
bool Foam::face::sameVertices(const face& a, const face& b)
{
    const label sizeA = a.size();
    const label sizeB = b.size();
 
    // Trivial reject: faces are different size
    if (sizeA != sizeB)
    {
        return false;
    }
    // Trivial: face with a single vertex
    else if (sizeA == 1)
    {
        return (a[0] == b[0]);
    }
 
    forAll(a, i)
    {
        // Count occurrences of a[i] in a
        label aOcc = 0;
        forAll(a, j)
        {
            if (a[i] == a[j]) aOcc++;
        }
 
        // Count occurrences of a[i] in b
        label bOcc = 0;
        forAll(b, j)
        {
            if (a[i] == b[j]) bOcc++;
        }
 
        // Check if occurrences of a[i] in a and b are the same
        if (aOcc != bOcc) return false;
    }
 
    return true;
}
 
 
unsigned Foam::face::symmhash_code(const UList<label>& f, unsigned seed)
{
    Foam::Hash<label> op;
 
    label len = f.size();
 
    if (!len)
    {
        // Trivial: zero-sized
        return 0;
    }
    else if (len == 1)
    {
        // Trivial: single vertex
        return op(f[0], seed);
    }
 
    // Find location of the min vertex
    label pivot = 0;
    for (label i = 1; i < len; ++i)
    {
        if (f[pivot] > f[i])
        {
            pivot = i;
        }
    }
 
    // Use next lowest value for deciding direction to circulate
    if (f.fcValue(pivot) < f.rcValue(pivot))
    {
        // Forward circulate
        while (len--)
        {
            seed = op(f[pivot], seed);
            pivot = f.fcIndex(pivot);
        }
    }
    else
    {
        // Reverse circulate
        while (len--)
        {
            seed = op(f[pivot], seed);
            pivot = f.rcIndex(pivot);
        }
    }
 
    return seed;
}
 
 
// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
Foam::label Foam::face::collapse()
{
    if (size() > 1)
    {
        label ci = 0;
        for (label i=1; i<size(); i++)
        {
            if (operator[](i) != operator[](ci))
            {
                operator[](++ci) = operator[](i);
            }
        }
 
        if (operator[](ci) != operator[](0))
        {
            ++ci;
        }
 
        setSize(ci);
    }
 
    return size();
}
 
 
void Foam::face::flip()
{
    const label n = size();
 
    if (n > 2)
    {
        for (label i=1; i < (n+1)/2; ++i)
        {
            std::swap(operator[](i), operator[](n-i));
        }
    }
}
 
 
Foam::point Foam::face::centre(const UList<point>& points) const
{
    // Calculate the centre by breaking the face into triangles and
    // area-weighted averaging their centres
 
    const label nPoints = size();
 
    // If the face is a triangle, do a direct calculation
    if (nPoints == 3)
    {
        return triPointRef::centre
        (
            points[operator[](0)],
            points[operator[](1)],
            points[operator[](2)]
        );
    }
    // else if (nPoints == 0)
    // {
    //     // Should not happen
    //     return Zero;
    // }
 
 
    // Note: use double precision to avoid overflows when summing
 
    // Estimated centre by averaging the face points
    const point centrePoint(this->average(points));
 
    doubleScalar sumA(0);
    doubleVector sumAc(Zero);
 
    for (label pI = 0; pI < nPoints; ++pI)
    {
        const label nextPti(pI == nPoints-1 ? 0 : pI+1);
        const auto& thisPoint = points[operator[](pI)];
        const auto& nextPoint = points[operator[](nextPti)];
 
        // Calculate 3*triangle centre
        const vector ttc(thisPoint + nextPoint + centrePoint);
 
        // Calculate 2*triangle area
        const scalar ta = Foam::mag
        (
            (thisPoint - centrePoint)
          ^ (nextPoint - centrePoint)
        );
 
        sumA += ta;
        sumAc += ta*ttc;
    }
 
    if (sumA > VSMALL)
    {
        return sumAc/(3.0*sumA);
    }
    else
    {
        return centrePoint;
    }
}
 
 
Foam::vector Foam::face::areaNormal(const UList<point>& points) const
{
    const label nPoints = size();
 
    // Calculate the area normal by summing the face triangle area normals.
    // Changed to deal with small concavity by using a central decomposition
 
    // If the face is a triangle, do a direct calculation
    if (nPoints == 3)
    {
        return triPointRef::areaNormal
        (
            points[operator[](0)],
            points[operator[](1)],
            points[operator[](2)]
        );
    }
    // else if (nPoints == 0)
    // {
    //     // Should not happen
    //     return Zero;
    // }
 
    // Estimated centre by averaging the face points
    const point centrePoint(this->average(points));
 
    vector n(Zero);
 
    for (label pI = 0; pI < nPoints; ++pI)
    {
        const label nextPti(pI == nPoints-1 ? 0 : pI+1);
        const auto& thisPoint = points[operator[](pI)];
        const auto& nextPoint = points[operator[](nextPti)];
 
        // Note: for best accuracy, centre point always comes last
 
        n += triPointRef::areaNormal(thisPoint, nextPoint, centrePoint);
    }
 
    return n;
}
 
 
Foam::face Foam::face::reverseFace() const
{
    // Reverse the label list and return
    // The starting points of the original and reverse face are identical.
 
    const labelUList& origFace = *this;
    const label len = origFace.size();
 
    face newFace(len);
    if (len)
    {
        newFace[0] = origFace[0];
        for (label i=1; i < len; ++i)
        {
            newFace[i] = origFace[len - i];
        }
    }
 
    return newFace;
}
 
 
Foam::scalar Foam::face::sweptVol
(
    const UList<point>& oldPoints,
    const UList<point>& newPoints
) const
{
    // This Optimization causes a small discrepancy between the swept-volume of
    // opposite faces of complex cells with triangular faces opposing polygons.
    // It could be used without problem for tetrahedral cells
    // if (size() == 3)
    // {
    //     return
    //     (
    //         triPointRef
    //         (
    //             oldPoints[operator[](0)],
    //             oldPoints[operator[](1)],
    //             oldPoints[operator[](2)]
    //         ).sweptVol
    //         (
    //             triPointRef
    //             (
    //                 newPoints[operator[](0)],
    //                 newPoints[operator[](1)],
    //                 newPoints[operator[](2)]
    //             )
    //         )
    //     );
    // }
 
    scalar sv = 0;
 
    // Calculate the swept volume by breaking the face into triangles and
    // summing their swept volumes.
    // Changed to deal with small concavity by using a central decomposition
 
    const point centreOldPoint = centre(oldPoints);
    const point centreNewPoint = centre(newPoints);
 
    const label nPoints = size();
 
    for (label pi=0; pi<nPoints-1; ++pi)
    {
        // Note: for best accuracy, centre point always comes last
        sv += triPointRef
        (
            centreOldPoint,
            oldPoints[operator[](pi)],
            oldPoints[operator[](pi + 1)]
        ).sweptVol
        (
            triPointRef
            (
                centreNewPoint,
                newPoints[operator[](pi)],
                newPoints[operator[](pi + 1)]
            )
        );
    }
 
    sv += triPointRef
    (
        centreOldPoint,
        oldPoints[operator[](nPoints-1)],
        oldPoints[operator[](0)]
    ).sweptVol
    (
        triPointRef
        (
            centreNewPoint,
            newPoints[operator[](nPoints-1)],
            newPoints[operator[](0)]
        )
    );
 
    return sv;
}
 
 
Foam::tensor Foam::face::inertia
(
    const UList<point>& p,
    const point& refPt,
    scalar density
) const
{
    // If the face is a triangle, do a direct calculation
    if (size() == 3)
    {
        return triPointRef
        (
            p[operator[](0)],
            p[operator[](1)],
            p[operator[](2)]
        ).inertia(refPt, density);
    }
 
    const point ctr = centre(p);
 
    tensor J = Zero;
 
    forAll(*this, i)
    {
        J += triPointRef
        (
            p[operator[](i)],
            p[operator[](fcIndex(i))],
            ctr
        ).inertia(refPt, density);
    }
 
    return J;
}
 
 
Foam::edgeList Foam::face::edges() const
{
    const labelList& verts = *this;
    const label nVerts = verts.size();
 
    edgeList theEdges(nVerts);
 
    // Last edge closes the polygon
    theEdges.back().first() = verts.back();
    theEdges.back().second() = verts.front();
 
    for (label verti = 0; verti < nVerts - 1; ++verti)
    {
        theEdges[verti].first() = verts[verti];
        theEdges[verti].second() = verts[verti + 1];
    }
 
    return theEdges;
}
 
 
Foam::edgeList Foam::face::rcEdges() const
{
    const labelList& verts = *this;
    const label nVerts = verts.size();
 
    edgeList theEdges(nVerts);
 
    // First edge closes the polygon
    theEdges.front().first() = verts.front();
    theEdges.front().second() = verts.back();
 
    for (label verti = 1; verti < nVerts; ++verti)
    {
        theEdges[verti].first() = verts[nVerts - verti];
        theEdges[verti].second() = verts[nVerts - verti - 1];
    }
 
    return theEdges;
}
 
 
Foam::label Foam::face::find(const Foam::edge& e) const
{
    const label idx = labelList::find(e.first());
 
    // NB: the point index is simultaneously the edge index.
    // ie, face point 0 starts edge 0, point 1 starts edge 1, ...
 
    if (idx != -1)
    {
        if (e.second() == nextLabel(idx))
        {
            // Current edge matches forward
            return idx;
        }
        if (e.second() == prevLabel(idx))
        {
            // Previous edge matches reverse
            return rcIndex(idx);
        }
    }
 
    return -1;  // Not found
}
 
 
int Foam::face::edgeDirection(const Foam::edge& e) const
{
    const label idx = labelList::find(e.first());
 
    if (idx != -1)
    {
        if (e.second() == nextLabel(idx))
        {
            // Current edge matches forward. Could encode: (idx+1)
            return 1;
        }
        if (e.second() == prevLabel(idx))
        {
            // Previous edge matches reverse. Could encode: -(rcIndex(idx)+1)
            return -1;
        }
    }
 
    return 0;  // Not found
}
 
 
Foam::label Foam::face::nTriangles(const UList<point>&) const
{
    return nTriangles();
}
 
 
Foam::label Foam::face::triangles
(
    const UList<point>& points,
    label& triI,
    faceList& triFaces
) const
{
    label quadI = 0;
    faceList quadFaces;
 
    return split(SPLITTRIANGLE, points, triI, quadI, triFaces, quadFaces);
}
 
 
Foam::label Foam::face::nTrianglesQuads
(
    const UList<point>& points,
    label& triI,
    label& quadI
) const
{
    faceList triFaces;
    faceList quadFaces;
 
    return split(COUNTQUAD, points, triI, quadI, triFaces, quadFaces);
}
 
 
Foam::label Foam::face::trianglesQuads
(
    const UList<point>& points,
    label& triI,
    label& quadI,
    faceList& triFaces,
    faceList& quadFaces
) const
{
    return split(SPLITQUAD, points, triI, quadI, triFaces, quadFaces);
}
 
 
Foam::label Foam::face::longestEdge(const UList<point>& pts) const
{
    const labelList& verts = *this;
    const label nVerts = verts.size();
 
    // Last edge closes the polygon. Use it to initialize loop
    label longest = nVerts - 1;
    scalar longestLen = pts[verts.front()].distSqr(pts[verts.back()]);
 
    // Examine other edges
    for (label edgei = 0; edgei < nVerts - 1; ++edgei)
    {
        scalar edgeLen = pts[verts[edgei]].distSqr(pts[verts[edgei+1]]);
 
        if (longestLen < edgeLen)
        {
            longest = edgei;
            longestLen = edgeLen;
        }
    }
 
    return longest;
}
 
 
// ************************************************************************* //