Add support for IfcSectionedSurface

This commit is contained in:
Thomas Krijnen
2024-09-12 11:20:30 +02:00
parent 35a4d87a65
commit 2545769f67
11 changed files with 361 additions and 194 deletions
+203
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@@ -0,0 +1,203 @@
#include "profile_helper.h"
#include "infra_sweep_helper.h"
#include "piecewise_function_evaluator.h"
#include <boost/range/combine.hpp>
using namespace ifcopenshell::geometry;
namespace {
// std::lerp when upgrading to C++ 20
template <typename T>
T lerp(const T& a, const T& b, double t) {
return a + t * (b - a);
}
}
taxonomy::loft::ptr ifcopenshell::geometry::make_loft(const Settings& settings_, const IfcUtil::IfcBaseClass* inst, const taxonomy::piecewise_function::ptr& pwf, std::vector<cross_section>& cross_sections)
{
std::sort(cross_sections.begin(), cross_sections.end());
auto loft = taxonomy::make<taxonomy::loft>();
// @todo intialize as default
loft->axis = nullptr;
// @todo currently only the case is handled where directrix returns a piecewise_function
// @todo this "if" statement is not really required because the function returns at the start if the Directrix is not a piecewise function
if (pwf) {
piecewise_function_evaluator evaluator(pwf, &settings_);
double start = std::max(0., cross_sections.front().dist_along);
double end = std::min(pwf->length(), cross_sections.back().dist_along);
if (end - start < 1.e-9) {
Logger::Warning("Empty sweep domain with start at " + std::to_string(cross_sections.front().dist_along) + " end at " + std::to_string(cross_sections.back().dist_along) + " and curve domain length " + std::to_string(pwf->length()), inst);
return nullptr;
}
auto curve_length = end - start;
auto param_type = settings_.get<ifcopenshell::geometry::settings::PiecewiseStepType>().get();
auto param = settings_.get<ifcopenshell::geometry::settings::PiecewiseStepParam>().get();
size_t num_steps = 0;
if (param_type == ifcopenshell::geometry::settings::PiecewiseStepMethod::MAXSTEPSIZE) {
// parameter is max step size
num_steps = (size_t)std::ceil(curve_length / param);
} else {
// parameter is minimum number of steps
num_steps = (size_t)std::ceil(param);
}
std::vector<double> longitudes;
for (auto& x : cross_sections) {
longitudes.push_back(x.dist_along);
}
longitudes.push_back(std::numeric_limits<double>::infinity());
auto profile_index = longitudes.begin();
for (size_t i = 0; i <= num_steps; ++i) {
auto dist_along = start + curve_length / num_steps * i;
while (dist_along > *(profile_index + 1)) {
profile_index++;
if (profile_index == longitudes.end()) {
// @todo handle this?
}
}
auto relative_dist_along = (dist_along - *profile_index) / (*(profile_index + 1) - *profile_index);
const auto& profile_a = cross_sections[std::distance(longitudes.begin(), profile_index)].section_geometry;
const auto& offset_a = cross_sections[std::distance(longitudes.begin(), profile_index)].offset;
taxonomy::geom_item::ptr interpolated = nullptr;
// Only interpolate if:
// - there is a profile ahead of us, and
// - we're not exactly at the location of the current profile or whether there is an offset involved.
bool should_interpolate =
(profile_index + 1 < longitudes.end()) &&
(relative_dist_along >= 1.e-9 || offset_a.cwiseAbs().maxCoeff() > 0.);
if (should_interpolate) {
taxonomy::geom_item::ptr profile_b;
Eigen::Vector3d offset_b;
if ((profile_index + 1 < longitudes.end())) {
profile_b = cross_sections[std::distance(longitudes.begin(), profile_index) + 1].section_geometry;
offset_b = cross_sections[std::distance(longitudes.begin(), profile_index) + 1].offset;
} else {
profile_b = profile_a;
offset_b = offset_a;
}
// Only interpolate if the profiles are different or either of the offsets is non-zero
bool should_interpolate2 =
(profile_a->instance != profile_b->instance) ||
(offset_a.cwiseAbs().maxCoeff() > 0. || offset_b.cwiseAbs().maxCoeff() > 0.);
if (should_interpolate2) {
std::vector<taxonomy::loop::ptr> loops_a, loops_b;
if (profile_a->kind() == taxonomy::FACE) {
interpolated = taxonomy::make<taxonomy::face>();
auto profile_a_f = std::static_pointer_cast<taxonomy::face>(profile_a);
auto profile_b_f = std::static_pointer_cast<taxonomy::face>(profile_b);
if (profile_a_f->children.size() != profile_b_f->children.size()) {
Logger::Warning("Mismatching number of face boundaries: " +
std::to_string(profile_a_f->children.size()) + " vs " +
std::to_string(profile_b_f->children.size()),
inst
);
return nullptr;
}
loops_a = profile_a_f->children;
loops_b = profile_b_f->children;
} else {
loops_a = { std::static_pointer_cast<taxonomy::loop>(profile_a) };
loops_b = { std::static_pointer_cast<taxonomy::loop>(profile_b) };
interpolated = taxonomy::make<taxonomy::loop>();
}
// @todo should_interpolate should also be informed based by different face matrices.
if (profile_a->matrix || profile_b->matrix) {
interpolated->matrix = taxonomy::make<taxonomy::matrix4>();
Eigen::Matrix4d m4a = Eigen::Matrix4d::Identity();
Eigen::Matrix4d m4b = Eigen::Matrix4d::Identity();
if (profile_a->matrix) {
m4a = profile_a->matrix->ccomponents();
}
if (profile_b->matrix) {
m4b = profile_b->matrix->ccomponents();
}
interpolated->matrix->components() = lerp(m4a, m4b, relative_dist_along);
}
auto interpolated_offset = lerp(offset_a, offset_b, relative_dist_along);
taxonomy::loop::ptr w1, w2;
taxonomy::edge::ptr e1, e2;
for (auto tmp_ : boost::combine(loops_a, loops_b)) {
boost::tie(w1, w2) = tmp_;
if (w1->children.size() != w2->children.size()) {
Logger::Warning("Mismatching number of edges: " +
std::to_string(w1->children.size()) + " vs " +
std::to_string(w2->children.size()),
inst
);
return nullptr;
}
std::vector<taxonomy::point3::ptr> points;
for (auto tmp__ : boost::combine(w1->children, w2->children)) {
boost::tie(e1, e2) = tmp__;
auto& p1 = boost::get<taxonomy::point3::ptr>(e1->start);
auto& p2 = boost::get<taxonomy::point3::ptr>(e2->start);
auto p3 = (lerp(p1->ccomponents(), p2->ccomponents(), relative_dist_along) + interpolated_offset).eval();
points.push_back(taxonomy::make<taxonomy::point3>(p3));
}
if (!points.empty()) {
// close polygon by referencing first point
// @todo add a closed=true|false to polygon_from_points()?
points.push_back(points.front());
}
auto interpolated_loop = polygon_from_points(points);
if (interpolated->kind() == taxonomy::FACE) {
std::static_pointer_cast<taxonomy::face>(interpolated)->children.push_back(interpolated_loop);
} else {
std::static_pointer_cast<taxonomy::loop>(interpolated)->children = interpolated_loop->children;
}
}
}
}
auto m4 = evaluator.evaluate(dist_along);
/* {
std::wcout << "#" << pwf->instance->data().id() << " " << dist_along << ": " << m4.col(3).row(2).value() << std::endl;
}*/
Eigen::Matrix4d m4b = Eigen::Matrix4d::Identity();
m4b.col(0).head<3>() = m4.col(1).head<3>().normalized();
m4b.col(1).head<3>() = m4.col(2).head<3>().normalized();
m4b.col(2).head<3>() = m4.col(0).head<3>().normalized();
m4b.col(3).head<3>() = m4.col(3).head<3>();
if (interpolated) {
loft->children.push_back(interpolated);
} else {
if (profile_a->kind() == taxonomy::FACE) {
loft->children.push_back(std::static_pointer_cast<taxonomy::face>(taxonomy::item::ptr(profile_a->clone_())));
} else {
loft->children.push_back(std::static_pointer_cast<taxonomy::loop>(taxonomy::item::ptr(profile_a->clone_())));
}
if (profile_a->matrix) {
loft->children.back()->matrix = taxonomy::matrix4::ptr(profile_a->matrix->clone_());
}
}
if (!loft->children.back()->matrix) {
// @todo should this not be initialized by default? matrix4 already has a 'lazy identity' mechanism.
loft->children.back()->matrix = taxonomy::make<taxonomy::matrix4>();
}
auto m = (m4b * loft->children.back()->matrix->ccomponents()).eval();
loft->children.back()->matrix->components() = m;
}
}
return loft;
}
+26
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@@ -0,0 +1,26 @@
#ifndef LINEAR_SWEEP_HELPER_H
#define LINEAR_SWEEP_HELPER_H
#include "taxonomy.h"
#include "ConversionSettings.h"
namespace ifcopenshell {
namespace geometry {
struct cross_section {
double dist_along;
taxonomy::geom_item::ptr section_geometry;
Eigen::Vector3d offset;
bool operator <(const cross_section& other) const {
return dist_along < other.dist_along;
}
};
taxonomy::loft::ptr make_loft(const Settings& settings_, const IfcUtil::IfcBaseClass* inst, const taxonomy::piecewise_function::ptr& directrix, std::vector<cross_section>& cross_sections);
}
}
#endif
+29 -12
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@@ -48,26 +48,43 @@ bool OpenCascadeKernel::convert(const taxonomy::loft::ptr loft, TopoDS_Shape& re
for (auto it = loft->children.begin(); it < loft->children.end() - 1; ++it) {
auto jt = it + 1;
std::array<taxonomy::face::ptr, 2> fa = { *it, *jt };
std::array<taxonomy::item::ptr, 2> fa = { *it, *jt };
std::array<TopoDS_Shape, 2> shps;
std::array<TopoDS_Wire, 2> ws;
for (int i = 0; i < 2; ++i) {
if (!convert(fa[i], shps[i])) {
return false;
if (fa[i]->kind() == taxonomy::FACE) {
if (!convert(std::static_pointer_cast<taxonomy::face>(fa[i]), shps[i])) {
return false;
}
}
if (shps[i].ShapeType() != TopAbs_FACE) {
if (fa[i]->kind() == taxonomy::LOOP) {
TopoDS_Wire w;
if (!convert(std::static_pointer_cast<taxonomy::loop>(fa[i]), w)) {
return false;
}
shps[i] = w;
}
if (shps[i].ShapeType() != TopAbs_FACE && shps[i].ShapeType() != TopAbs_WIRE) {
return false;
}
// @todo this is only outer wire
ws[i] = BRepTools::OuterWire(TopoDS::Face(shps[i]));
if (shps[i].ShapeType() == TopAbs_FACE) {
ws[i] = BRepTools::OuterWire(TopoDS::Face(shps[i]));
} else {
ws[i] = TopoDS::Wire(shps[i]);
}
}
if (it == loft->children.begin()) {
// faces.Append(shps[0]);
BB.Add(comp, shps[0]);
}
if (jt == loft->children.end() - 1) {
// faces.Append(shps[1]);
BB.Add(comp, shps[1]);
if (shps[0].ShapeType() == TopAbs_FACE) {
// When processing a sectioned *surface* there are no
// begin and end caps that need to be added.
if (it == loft->children.begin()) {
// faces.Append(shps[0]);
BB.Add(comp, shps[0]);
}
if (jt == loft->children.end() - 1) {
// faces.Append(shps[1]);
BB.Add(comp, shps[1]);
}
}
BRepTools_WireExplorer a(ws[0]);
BRepTools_WireExplorer b(ws[1]);
@@ -22,29 +22,10 @@
using namespace ifcopenshell::geometry;
#include "../../ifcgeom/profile_helper.h"
#include "../piecewise_function_evaluator.h"
#include <boost/range/combine.hpp>
#include "../../ifcgeom/infra_sweep_helper.h"
#ifdef SCHEMA_HAS_IfcSectionedSolidHorizontal
namespace {
// std::lerp when upgrading to C++ 20
template <typename T>
T lerp(const T& a, const T& b, double t) {
return a + t * (b - a);
}
struct cross_section {
double dist_along;
taxonomy::face::ptr section_geometry;
Eigen::Vector3d offset;
bool operator <(const cross_section& other) const {
return dist_along < other.dist_along;
}
};
}
taxonomy::ptr mapping::map_impl(const IfcSchema::IfcSectionedSolidHorizontal* inst) {
std::vector<cross_section> cross_sections;
@@ -106,163 +87,7 @@ taxonomy::ptr mapping::map_impl(const IfcSchema::IfcSectionedSolidHorizontal* in
}
}
std::sort(cross_sections.begin(), cross_sections.end());
auto loft = taxonomy::make<taxonomy::loft>();
// @todo intialize as default
loft->axis = nullptr;
// @todo currently only the case is handled where directrix returns a piecewise_function
// @todo this "if" statement is not really required because the function returns at the start if the Directrix is not a piecewise function
if (pwf) {
piecewise_function_evaluator evaluator(pwf, &settings_);
double start = std::max(0., cross_sections.front().dist_along);
double end = std::min(pwf->length(), cross_sections.back().dist_along);
if (end - start < 1.e-9) {
Logger::Warning("Empty sweep domain with start at " + std::to_string(cross_sections.front().dist_along) + " end at " + std::to_string(cross_sections.back().dist_along) + " and curve domain length " + std::to_string(pwf->length()), inst);
return nullptr;
}
auto curve_length = end - start;
auto param_type = settings_.get<ifcopenshell::geometry::settings::PiecewiseStepType>().get();
auto param = settings_.get<ifcopenshell::geometry::settings::PiecewiseStepParam>().get();
size_t num_steps = 0;
if (param_type == ifcopenshell::geometry::settings::PiecewiseStepMethod::MAXSTEPSIZE) {
// parameter is max step size
num_steps = (size_t) std::ceil(curve_length / param);
} else {
// parameter is minimum number of steps
num_steps = (size_t) std::ceil(param);
}
std::vector<double> longitudes;
for (auto& x : cross_sections) {
longitudes.push_back(x.dist_along);
}
longitudes.push_back(std::numeric_limits<double>::infinity());
auto profile_index = longitudes.begin();
for (size_t i = 0; i <= num_steps; ++i) {
auto dist_along = start + curve_length / num_steps * i;
while (dist_along > *(profile_index+1)) {
profile_index++;
if (profile_index == longitudes.end()) {
// @todo handle this?
}
}
auto relative_dist_along = (dist_along - *profile_index) / (*(profile_index+1) - *profile_index);
const auto& profile_a = cross_sections[std::distance(longitudes.begin(), profile_index)].section_geometry;
const auto& offset_a = cross_sections[std::distance(longitudes.begin(), profile_index)].offset;
taxonomy::face::ptr interpolated = nullptr;
// Only interpolate if:
// - there is a profile ahead of us, and
// - we're not exactly at the location of the current profile or whether there is an offset involved.
bool should_interpolate =
(profile_index + 1 < longitudes.end()) &&
(relative_dist_along >= 1.e-9 || offset_a.cwiseAbs().maxCoeff() > 0.);
if (should_interpolate) {
taxonomy::face::ptr profile_b;
Eigen::Vector3d offset_b;
if ((profile_index + 1 < longitudes.end())) {
profile_b = cross_sections[std::distance(longitudes.begin(), profile_index) + 1].section_geometry;
offset_b = cross_sections[std::distance(longitudes.begin(), profile_index) + 1].offset;
} else {
profile_b = profile_a;
offset_b = offset_a;
}
// Only interpolate if the profiles are different or either of the offsets is non-zero
bool should_interpolate2 =
(profile_a->instance != profile_b->instance) ||
(offset_a.cwiseAbs().maxCoeff() > 0. || offset_b.cwiseAbs().maxCoeff() > 0.);
if (should_interpolate2) {
if (profile_a->children.size() != profile_b->children.size()) {
Logger::Warning("Mismatching number of face boundaries: " +
std::to_string(profile_a->children.size()) + " vs " +
std::to_string(profile_b->children.size()),
inst
);
return nullptr;
}
interpolated = taxonomy::make<taxonomy::face>();
// @todo should_interpolate should also be informed based by different face matrices.
if (profile_a->matrix || profile_b->matrix) {
interpolated->matrix = taxonomy::make<taxonomy::matrix4>();
Eigen::Matrix4d m4a = Eigen::Matrix4d::Identity();
Eigen::Matrix4d m4b = Eigen::Matrix4d::Identity();
if (profile_a->matrix) {
m4a = profile_a->matrix->ccomponents();
}
if (profile_b->matrix) {
m4b = profile_b->matrix->ccomponents();
}
interpolated->matrix->components() = lerp(m4a, m4b, relative_dist_along);
}
auto interpolated_offset = lerp(offset_a, offset_b, relative_dist_along);
taxonomy::loop::ptr w1, w2;
taxonomy::edge::ptr e1, e2;
for (auto tmp_ : boost::combine(profile_a->children, profile_b->children)) {
boost::tie(w1, w2) = tmp_;
if (w1->children.size() != w2->children.size()) {
Logger::Warning("Mismatching number of edges for face boundary: " +
std::to_string(w1->children.size()) + " vs " +
std::to_string(w2->children.size()),
inst
);
return nullptr;
}
std::vector<taxonomy::point3::ptr> points;
for (auto tmp__ : boost::combine(w1->children, w2->children)) {
boost::tie(e1, e2) = tmp__;
auto& p1 = boost::get<taxonomy::point3::ptr>(e1->start);
auto& p2 = boost::get<taxonomy::point3::ptr>(e2->start);
auto p3 = (lerp(p1->ccomponents(), p2->ccomponents(), relative_dist_along) + interpolated_offset).eval();
points.push_back(taxonomy::make<taxonomy::point3>(p3));
}
if (!points.empty()) {
// close polygon by referencing first point
// @todo add a closed=true|false to polygon_from_points()?
points.push_back(points.front());
}
interpolated->children.push_back(polygon_from_points(points));
}
}
}
auto m4 = evaluator.evaluate(dist_along);
/* {
std::wcout << "#" << pwf->instance->data().id() << " " << dist_along << ": " << m4.col(3).row(2).value() << std::endl;
}*/
Eigen::Matrix4d m4b = Eigen::Matrix4d::Identity();
m4b.col(0).head<3>() = m4.col(1).head<3>().normalized();
m4b.col(1).head<3>() = m4.col(2).head<3>().normalized();
m4b.col(2).head<3>() = m4.col(0).head<3>().normalized();
m4b.col(3).head<3>() = m4.col(3).head<3>();
if (interpolated) {
loft->children.push_back(interpolated);
} else {
loft->children.push_back(taxonomy::face::ptr(profile_a->clone_()));
if (profile_a->matrix) {
loft->children.back()->matrix = taxonomy::matrix4::ptr(profile_a->matrix->clone_());
}
}
if (!loft->children.back()->matrix) {
// @todo should this not be initialized by default? matrix4 already has a 'lazy identity' mechanism.
loft->children.back()->matrix = taxonomy::make<taxonomy::matrix4>();
}
auto m = (m4b * loft->children.back()->matrix->ccomponents()).eval();
loft->children.back()->matrix->components() = m;
}
}
return loft;
return make_loft(settings_, inst, pwf, cross_sections);
}
#endif
@@ -0,0 +1,93 @@
/********************************************************************************
* *
* This file is part of IfcOpenShell. *
* *
* IfcOpenShell is free software: you can redistribute it and/or modify *
* it under the terms of the Lesser GNU General Public License as published by *
* the Free Software Foundation, either version 3.0 of the License, or *
* (at your option) any later version. *
* *
* IfcOpenShell 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 *
* Lesser GNU General Public License for more details. *
* *
* You should have received a copy of the Lesser GNU General Public License *
* along with this program. If not, see <http://www.gnu.org/licenses/>. *
* *
********************************************************************************/
#include "mapping.h"
#define mapping POSTFIX_SCHEMA(mapping)
using namespace ifcopenshell::geometry;
#include "../../ifcgeom/profile_helper.h"
#include "../../ifcgeom/infra_sweep_helper.h"
#ifdef SCHEMA_HAS_IfcSectionedSurface
taxonomy::ptr mapping::map_impl(const IfcSchema::IfcSectionedSurface* inst) {
std::vector<cross_section> cross_sections;
auto dir = map(inst->Directrix());
auto pwf = taxonomy::dcast<taxonomy::piecewise_function>(dir);
if (!pwf) {
// Only implement on alignment curves
Logger::Warning("IfcSectionedSurface is only implemented for piecewise function Directrix curves", inst);
return nullptr;
}
{
auto css = inst->CrossSections();
auto csps = inst->CrossSectionPositions();
std::vector<taxonomy::geom_item::ptr> faces;
// The PointByDistanceExpressesions are factored out into (a) a cartesian offset relative to the
// reference frame along a certain curve location (b) the longitude.
// The longitudes determine the range of the sweep and the offsets are interpolated in between
// sweep segments.
std::vector<Eigen::Vector3d> profile_offsets;
std::vector<double> longitudes;
for (auto& cs : *css) {
faces.push_back(std::move(taxonomy::cast<taxonomy::geom_item>(map(cs))));
}
#ifdef SCHEMA_HAS_IfcPointByDistanceExpression
for (auto& csp : *csps) {
auto pbde = csp->Location()->as<IfcSchema::IfcPointByDistanceExpression>(true);
longitudes.push_back(*pbde->DistanceAlong()->as<IfcSchema::IfcLengthMeasure>(true) * length_unit_);
// Corresponds to the profile X, Y directions (hopefully).
Eigen::Vector3d po(
pbde->OffsetLateral().get_value_or(0.),
// @todo I don't understand whether vertical is an offset relative to the tangent plane or to the global XY plane
pbde->OffsetVertical().get_value_or(0.),
0.
);
profile_offsets.push_back(po);
}
#else
return nullptr;
#endif
if (faces.size() != profile_offsets.size()) {
Logger::Warning("Expected CrossSections and CrossSectionPositions to be equal length, but got " + std::to_string(faces.size()) + " and " + std::to_string(profile_offsets.size()) + " respectively", inst);
return nullptr;
}
if (faces.size() < 2) {
Logger::Warning("Expected at least two cross sections, but got " + std::to_string(faces.size()), inst);
return nullptr;
}
for (size_t i = 0; i < faces.size(); ++i) {
cross_sections.push_back({ longitudes[i], faces[i], profile_offsets[i] });
}
}
return make_loft(settings_, inst, pwf, cross_sections);
}
#endif
+3
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@@ -135,6 +135,9 @@ BIND(IfcFixedReferenceSweptAreaSolid)
#ifdef SCHEMA_HAS_IfcSectionedSolidHorizontal
BIND(IfcSectionedSolidHorizontal)
#endif
#ifdef SCHEMA_HAS_IfcSectionedSurface
BIND(IfcSectionedSurface)
#endif
BIND(IfcCircle);
BIND(IfcEllipse);
+1 -1
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@@ -4,7 +4,7 @@
using namespace ifcopenshell::geometry;
piecewise_function_evaluator::piecewise_function_evaluator(taxonomy::piecewise_function::const_ptr pwf, ifcopenshell::geometry::Settings* settings) : pwf_(pwf) {
piecewise_function_evaluator::piecewise_function_evaluator(taxonomy::piecewise_function::const_ptr pwf, const ifcopenshell::geometry::Settings* settings) : pwf_(pwf) {
if (settings) {
settings_ = *settings;
}
+1 -1
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@@ -10,7 +10,7 @@ namespace ifcopenshell { namespace geometry {
/// @brief utility class to evaluate piecewise_function objects
class piecewise_function_evaluator {
public:
piecewise_function_evaluator(taxonomy::piecewise_function::const_ptr pwf, ifcopenshell::geometry::Settings* settings=nullptr);
piecewise_function_evaluator(taxonomy::piecewise_function::const_ptr pwf, const ifcopenshell::geometry::Settings* settings=nullptr);
/// @brief returns a vector of "distance along" points where the evaluate function computes loop points
std::vector<double> evaluation_points() const;
+1 -1
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@@ -313,7 +313,7 @@ namespace {
}
bool compare(const loft& a, const loft& b) {
return compare_collection<face>(a, b);
return compare_collection<geom_item>(a, b);
}
bool compare(const collection& a, const collection& b) {
+1 -1
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@@ -810,7 +810,7 @@ typedef item const* ptr;
}
};
struct loft : public collection_base<face> {
struct loft : public collection_base<geom_item> {
DECLARE_PTR(loft)
item::ptr axis;
+1 -1
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@@ -316,7 +316,7 @@ assign_children_access(loop, edge);
assign_children_access(face, loop);
assign_children_access(shell, face);
assign_children_access(solid, shell);
assign_children_access(loft, face);
assign_children_access(loft, geom_item);
assign_children_access(boolean_result, geom_item);
%define assign_matrix_access(item_name)