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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 "surface/normalsurface.h"
#include "surface/normalsurfaces.h"
#include "triangulation/dim3.h"
namespace regina {
void NormalSurfaces::buildReducedFromStandard(
const std::vector<NormalSurface>& stdList) {
// Get the empty triangulation out of the way now.
unsigned long n = triangulation_->size();
if (n == 0)
return;
bool almostNormal = allowsAlmostNormal();
// We need to get rid of vertex links entirely before we start.
// Build a new list of pointers to the (non-vertex-linking) surfaces
// that we are interested in.
auto* use = new const NormalSurface*[stdList.size()];
size_t nUse = 0;
for (const NormalSurface& s : stdList)
if (! s.isVertexLinking())
use[nUse++] = &s;
// We want to take all surfaces with maximal zero sets in quad space.
// That is, we want surface S if and only if there is no other surface T
// where, for every quad coordinate where S is zero, T is zero also.
// For almost normal surfaces, simply replace "quad coordinate" with
// "quad or oct coordinate".
unsigned tet;
for (size_t i = 0; i < nUse; ++i) {
if (! use[i])
continue;
bool dominates = false;
bool strict = false;
for (size_t j = 0; j < nUse; ++j) {
if (j == i || ! use[j])
continue;
dominates = true;
strict = false;
for (tet = 0; tet < n && dominates; ++tet) {
// Check the zero/non-zero status of the quads.
for (int type = 0; type < 3; ++type) {
if (use[i]->quads(tet, type) == 0 &&
use[j]->quads(tet, type) != 0) {
dominates = false;
break;
} else if (use[i]->quads(tet, type) != 0 &&
use[j]->quads(tet, type) == 0) {
// If this *does* turn out to be a domination of
// zero sets, we know it's strict.
strict = true;
}
}
// Likewise for the octagons.
if (almostNormal && dominates) {
for (int type = 0; type < 3; ++type) {
if (use[i]->octs(tet, type) == 0 &&
use[j]->octs(tet, type) != 0) {
dominates = false;
break;
} else if (use[i]->octs(tet, type) != 0 &&
use[j]->octs(tet, type) == 0) {
strict = true;
}
}
}
}
if (dominates)
break;
}
if (! dominates) {
// We want this surface.
// Although we now have vertices in a different coordinate
// system, the encoding should not have changed.
// TODO: However.. we *should* give the encoding the extra
// flag that guarantees it is not vertex linking.
// Not doing so is harmless but a bit wasteful.
// However, the entire standard-to-quad conversion is also
// somewhat unnecessary and wasteful, so leave this alone for now.
surfaces_.push_back(*use[i]);
} else if (strict) {
// We can drop this surface entirely from our list.
// We don't want it for our final solution set, and if
// use[i] is going to rule out some *other* surface then
// use[j] will rule out that same other surface also.
//
// The domination need to be strict because otherwise we
// might want use[i] to rule out use[j] (i.e., they both
// rule out each other).
use[i] = nullptr;
}
}
delete[] use;
}
} // namespace regina
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