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/**************************************************************************
* *
* Regina - A Normal Surface Theory Calculator *
* Computational Engine *
* *
* Copyright (c) 1999-2025, Ben Burton *
* For further details contact Ben Burton (bab@debian.org). *
* *
* This program is free software; you can redistribute it and/or *
* modify it under the terms of the GNU General Public License as *
* published by the Free Software Foundation; either version 2 of the *
* License, or (at your option) any later version. *
* *
* As an exception, when this program is distributed through (i) the *
* App Store by Apple Inc.; (ii) the Mac App Store by Apple Inc.; or *
* (iii) Google Play by Google Inc., then that store may impose any *
* digital rights management, device limits and/or redistribution *
* restrictions that are required by its terms of service. *
* *
* This program is distributed in the hope that it will be useful, but *
* WITHOUT 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 *
* along with this program. If not, see <https://www.gnu.org/licenses/>. *
* *
**************************************************************************/
#include "subcomplex/pillowtwosphere.h"
#include "triangulation/dim3.h"
namespace regina {
std::unique_ptr<PillowTwoSphere> PillowTwoSphere::recognise(
Triangle<3>* tri1, Triangle<3>* tri2) {
if (tri1 == tri2 || tri1->isBoundary() || tri2->isBoundary())
return nullptr;
Edge<3>* edge[2][3];
int i;
for (i = 0; i < 3; i++) {
edge[0][i] = tri1->edge(i);
edge[1][i] = tri2->edge(i);
}
if (edge[0][0] == edge[0][1] || edge[0][0] == edge[0][2] ||
edge[0][1] == edge[0][2])
return nullptr;
// The first triangle has three distinct edges. See if it matches to the
// second triangle.
int joinTo0 = -1;
for (i = 0; i < 3; i++)
if (edge[0][0] == edge[1][i]) {
joinTo0 = i;
break;
}
if (joinTo0 == -1)
return nullptr;
// Now make sure the edges all match up and with the correct
// permutations.
Perm<4> perm = tri2->edgeMapping(joinTo0) * tri1->edgeMapping(0).inverse();
for (i = 1; i < 3; i++) {
if (edge[0][i] != edge[1][perm[i]])
return nullptr;
if (! (tri2->edgeMapping(perm[i]) == perm * tri1->edgeMapping(i)))
return nullptr;
}
// We have an answer.
//
// Note: we cannot use make_unique here, since the class
// constructor is private.
return std::unique_ptr<PillowTwoSphere>(new PillowTwoSphere(
tri1, tri2, perm));
}
void PillowTwoSphere::writeTextShort(std::ostream& out) const {
out << "Pillow 2-sphere, triangles "
<< triangle_[0]->index() << ", " << triangle_[1]->index();
}
} // namespace regina
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