FEPlaneCut.cpp

/*This file is part of the FEBio Studio source code and is licensed under the MIT license
listed below.

See Copyright-FEBio-Studio.txt for details.

Copyright (c) 2021 University of Utah, The Trustees of Columbia University in
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#include "stdafx.h"
#include "FEModifier.h"
#include <MeshLib/MeshMetrics.h>
using namespace std;

//-----------------------------------------------------------------------------
const int lut[14][3][4] = {
	{{ 0, 1, 2, 0},{-1,-1,-1,-1},{-1,-1,-1,-1}},
	{{ 0, 3, 5, 1},{ 1, 5, 3, 0},{ 1, 2, 5, 0}},
	{{ 0, 3, 4, 0},{ 1, 4, 3, 1},{ 0, 4, 2, 0}},
	{{ 0, 1, 5, 1},{ 1, 4, 5, 1},{ 2, 5, 4, 0}},
	{{ 0, 1, 5, 0},{ 1, 4, 5, 0},{ 2, 5, 4, 1}},
	{{ 0, 3, 4, 1},{ 1, 4, 3, 0},{ 0, 4, 2, 1}},
	{{ 0, 3, 5, 0},{ 1, 5, 3, 1},{ 1, 2, 5, 1}},
	{{ 0, 1, 2, 1},{-1,-1,-1,-1},{-1,-1,-1,-1}},
	{{ 0, 1, 4, 0},{ 0, 4, 2, 1},{-1,-1,-1,-1}},
	{{ 0, 1, 4, 1},{ 0, 4, 2, 0},{-1,-1,-1,-1}},
	{{ 0, 1, 5, 0},{ 1, 2, 5, 1},{-1,-1,-1,-1}},
	{{ 0, 1, 5, 1},{ 1, 2, 5, 0},{-1,-1,-1,-1}},
	{{ 0, 3, 2, 0},{ 1, 2, 3, 1},{-1,-1,-1,-1}},
	{{ 0, 3, 2, 1},{ 1, 2, 3, 0},{-1,-1,-1,-1}},
};

//-----------------------------------------------------------------------------
FEPlaneCut::FEPlaneCut() : FEModifier("Plane cut")
{
	m_a[0] = 1.0;
	m_a[1] = 0.0;
	m_a[2] = 0.0;
	m_a[3] = 0.0;
}

//-----------------------------------------------------------------------------
void FEPlaneCut::SetPlaneCoefficients(double a[4])
{
	m_a[0] = a[0];
	m_a[1] = a[1];
	m_a[2] = a[2];
	m_a[3] = a[3];
}

//-----------------------------------------------------------------------------
FSMesh* FEPlaneCut::Apply(FSMesh* pm)
{
	// make sure this is a triangle mesh
	if (pm->IsType(FE_TRI3) == false)
	{
		SetError("This is not a triangle mesh.");
		return nullptr;
	}

	// get the characteristic mesh size (i.e. smallest edge length)
	double h = 0.01*FEMeshMetrics::ShortestEdge(*pm);

	// nodal values
	int NN = pm->Nodes();
	vector<double> val(NN);
	for (int i=0; i<NN; ++i)
	{
		vec3d& r = pm->Node(i).r;
		val[i] = m_a[0]*r.x + m_a[1]*r.y + m_a[2]*r.z - m_a[3];
		if (fabs(val[i])<h) val[i] = 0.0;
	}

	// loop over all elements and determine case number
	const int NE = pm->Elements();
	for (int i=0; i<NE; ++i)
	{
		FSElement& ei = pm->Element(i);
		ei.m_ntag = 0;
		double v[3];
		v[0] = val[ei.m_node[0]]; 
		v[1] = val[ei.m_node[1]]; 
		v[2] = val[ei.m_node[2]]; 

		// check special cases first
		if ((v[0]==0.0)||(v[1]==0.0)||(v[2]==0.0))
		{
			ei.m_ntag = -1;

			// all three nodes are zero
			// NOTE: This should never happen unless all nodes are colinear
			if ((v[0]==0.0)&&(v[1]==0.0)&&(v[2]==0.0)) ei.m_ntag = 0;

			// two nodes are zero
			if ((v[0]==0.0)&&(v[1]==0.0)&&(v[2]<0.0)) ei.m_ntag = 0;
			if ((v[1]==0.0)&&(v[2]==0.0)&&(v[0]<0.0)) ei.m_ntag = 0;
			if ((v[2]==0.0)&&(v[0]==0.0)&&(v[1]<0.0)) ei.m_ntag = 0;

			if ((v[0]==0.0)&&(v[1]==0.0)&&(v[2]>0.0)) ei.m_ntag = 7;
			if ((v[1]==0.0)&&(v[2]==0.0)&&(v[0]>0.0)) ei.m_ntag = 7;
			if ((v[2]==0.0)&&(v[0]==0.0)&&(v[1]>0.0)) ei.m_ntag = 7;

			// one node is zero (other two on same side)
			if ((v[0]==0.0)&&(v[1]<0.0)&&(v[2]<0.0)) ei.m_ntag = 0;
			if ((v[1]==0.0)&&(v[2]<0.0)&&(v[0]<0.0)) ei.m_ntag = 0;
			if ((v[2]==0.0)&&(v[0]<0.0)&&(v[1]<0.0)) ei.m_ntag = 0;

			if ((v[0]==0.0)&&(v[1]>0.0)&&(v[2]>0.0)) ei.m_ntag = 7;
			if ((v[1]==0.0)&&(v[2]>0.0)&&(v[0]>0.0)) ei.m_ntag = 7;
			if ((v[2]==0.0)&&(v[0]>0.0)&&(v[1]>0.0)) ei.m_ntag = 7;

			// one node is zero (element is bisected)
			if ((v[0] == 0.0)&&(v[1]<0.0)&&(v[2]>0.0)) ei.m_ntag = 8;
			if ((v[0] == 0.0)&&(v[1]>0.0)&&(v[2]<0.0)) ei.m_ntag = 9;

			if ((v[1] == 0.0)&&(v[2]>0.0)&&(v[0]<0.0)) ei.m_ntag = 10;
			if ((v[1] == 0.0)&&(v[2]<0.0)&&(v[0]>0.0)) ei.m_ntag = 11;

			if ((v[2] == 0.0)&&(v[0]<0.0)&&(v[1]>0.0)) ei.m_ntag = 12;
			if ((v[2] == 0.0)&&(v[0]>0.0)&&(v[1]<0.0)) ei.m_ntag = 13;

			assert(ei.m_ntag != -1);
		}
		else
		{
			// handle general case
			if (v[0] > 0.0) ei.m_ntag |= 1;
			if (v[1] > 0.0) ei.m_ntag |= 2;
			if (v[2] > 0.0) ei.m_ntag |= 4;
		}
	}

	// counts new number of elements
	int NE2 = 0;
	for (int i=0; i<NE; ++i)
	{
		FSElement& ei = pm->Element(i);
		if ((ei.m_ntag > 0) && (ei.m_ntag < 7)) NE2 += 3;
		else if (ei.m_ntag > 7) NE2 += 2;
		else NE2++;
	}

	// determine the edge lists
	vector<EDGE> EL;			// list of all edges
	EL.reserve(NE2 - NE);
	vector<EDGELIST> EEL;		// list of element edges
	EEL.resize(NE);
	for (int i=0; i<NE; ++i)
	{
		FSElement& ei = pm->Element(i);
		for (int j=0; j<3; ++j)
		{
			int jp1 = (j+1)%3;
			double w0 = val[ei.m_node[j  ]];
			double w1 = val[ei.m_node[jp1]];
			if (w0*w1 < 0.0)
			{
				// add the edge
				EDGE e;
				e.n0 = ei.m_node[j  ];
				e.n1 = ei.m_node[jp1];
				e.w = w0/(w0 - w1);

				// make sure this edge does not exist yet
				int ne = (int) EL.size();
				int nedge = -1;
				for (int k=0; k<ne; ++k)
				{
					EDGE& ek = EL[k];
					if (((ek.n0 == e.n0)&&(ek.n1 == e.n1)) || ((ek.n0 == e.n1)&&(ek.n1 == e.n0))) { nedge = k; break; }
				}

				// if not found, add it to the list
				if (nedge == -1)
				{
					EL.push_back(e);
					nedge = ne;
				}

				// mark the element's edge
				EEL[i].n[j] = nedge;
			}
			else EEL[i].n[j] = -1;
		}
	}

	// create a new mesh
	FSMesh* pnew = new FSMesh;
	int N1 = (int) EL.size();		// number of new nodes (i.e. number of cut edges)
	pnew->Create(NN + N1, NE2);

	// copy nodes
	for (int i=0; i<NN; ++i) pnew->Node(i) = pm->Node(i);

	// add new nodes
	for (int i=0; i<N1; ++i)
	{
		FSNode& ni = pnew->Node(i + NN);
		vec3d& r0 = pm->Node(EL[i].n0).r;
		vec3d& r1 = pm->Node(EL[i].n1).r;
		ni.r = r0 + (r1 - r0)*EL[i].w;
	}

	// copy elements
	int ne = 0;
	for (int i=0; i<NE; ++i)
	{
		FSElement& es = pm->Element(i);

		// get the node numbers
		int n[6];
		n[0] = es.m_node[0];
		n[1] = es.m_node[1];
		n[2] = es.m_node[2];
		if (EEL[i].n[0] >= 0) n[3] = NN + EEL[i].n[0]; else n[3] = -1;
		if (EEL[i].n[1] >= 0) n[4] = NN + EEL[i].n[1]; else n[4] = -1;
		if (EEL[i].n[2] >= 0) n[5] = NN + EEL[i].n[2]; else n[5] = -1;

		for (int j=0; j<3; ++j)
		{
			const int *lj = lut[es.m_ntag][j];
			if (lj[0]==-1) break;
			FSElement& ed = pnew->Element(ne++);
			ed = es;
			ed.m_node[0] = n[lj[0]]; assert(ed.m_node[0] != -1);
			ed.m_node[1] = n[lj[1]]; assert(ed.m_node[1] != -1);
			ed.m_node[2] = n[lj[2]]; assert(ed.m_node[2] != -1);
			ed.m_gid = lj[3]; assert(lj[3] != -1);
		}
	}
	assert(ne == pnew->Elements());

	// next, we reconstruct all faces, edges and nodes
	pnew->RebuildMesh();

	return pnew;
}