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Finished implementing Boost.Polygon medial axis. Some cleanup needed

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This commit is contained in:
Alessandro Ranellucci 2014-01-10 16:18:55 +01:00
parent 07a4c37c4c
commit 7b0decbeb1
7 changed files with 117 additions and 194 deletions
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1
Build.PL
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@ -13,7 +13,6 @@ my %prereqs = qw(
File::Basename 0
File::Spec 0
Getopt::Long 0
Math::Geometry::Voronoi 1.3
Math::PlanePath 53
Module::Build::WithXSpp 0.14
Moo 1.003001

164
lib/Slic3r/ExPolygon.pm
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@ -5,7 +5,6 @@ use warnings;
# an ExPolygon is a polygon with holes
use List::Util qw(first);
use Math::Geometry::Voronoi;
use Slic3r::Geometry qw(X Y A B point_in_polygon epsilon scaled_epsilon);
use Slic3r::Geometry::Clipper qw(union_ex diff_pl);
@ -43,169 +42,6 @@ sub bounding_box {
return $self->contour->bounding_box;
}
# this method only works for expolygons having only a contour or
# a contour and a hole, and not being thicker than the supplied
# width. it returns a polyline or a polygon
sub ___medial_axis {
my ($self, $width) = @_;
return $self->_medial_axis_voronoi($width);
}
sub _medial_axis_clip {
my ($self, $width) = @_;
my $grow = sub {
my ($line, $distance) = @_;
my $line_clone = $line->clone;
$line_clone->clip_start(scaled_epsilon);
return () if !$line_clone->is_valid;
$line_clone->clip_end(scaled_epsilon);
return () if !$line_clone->is_valid;
my ($a, $b) = @$line_clone;
my $dx = $a->x - $b->x;
my $dy = $a->y - $b->y; #-
my $dist = sqrt($dx*$dx + $dy*$dy);
$dx /= $dist;
$dy /= $dist;
return Slic3r::Polygon->new(
Slic3r::Point->new($a->x + $distance*$dy, $a->y - $distance*$dx), #--
Slic3r::Point->new($b->x + $distance*$dy, $b->y - $distance*$dx), #--
Slic3r::Point->new($b->x - $distance*$dy, $b->y + $distance*$dx), #++
Slic3r::Point->new($a->x - $distance*$dy, $a->y + $distance*$dx), #++
);
};
my @result = ();
my $covered = [];
foreach my $polygon (@$self) {
my @polylines = ();
foreach my $line (@{$polygon->lines}) {
# remove the areas that are already covered from this line
my $clipped = diff_pl([$line->as_polyline], $covered);
# skip very short segments/dots
@$clipped = grep $_->length > $width/10, @$clipped;
# grow the remaining lines and add them to the covered areas
push @$covered, map $grow->($_, $width*1.1), @$clipped;
# if the first remaining segment is connected to the last polyline, append it
# to that -- FIXME: this assumes that diff_pl()
# preserved the orientation of the input linestring but this is not generally true
if (@polylines && @$clipped && $clipped->[0]->first_point->distance_to($polylines[-1]->last_point) <= $width/10) {
$polylines[-1]->append_polyline(shift @$clipped);
}
push @polylines, @$clipped;
}
foreach my $polyline (@polylines) {
# if this polyline looks like a closed loop, return it as a polygon
if ($polyline->first_point->coincides_with($polyline->last_point)) {
next if @$polyline == 2;
$polyline->pop_back;
push @result, Slic3r::Polygon->new(@$polyline);
} else {
push @result, $polyline;
}
}
}
return @result;
}
my $voronoi_lock :shared;
sub _medial_axis_voronoi {
my ($self, $width) = @_;
lock($voronoi_lock);
my $voronoi;
{
my @points = ();
foreach my $polygon (@$self) {
{
my $p = $polygon->pp;
Slic3r::Geometry::polyline_remove_short_segments($p, $width / 2);
$polygon = Slic3r::Polygon->new(@$p);
}
# subdivide polygon segments so that we don't have anyone of them
# being longer than $width / 2
$polygon = $polygon->subdivide($width/2);
push @points, @{$polygon->pp};
}
$voronoi = Math::Geometry::Voronoi->new(points => \@points);
}
$voronoi->compute;
my $vertices = $voronoi->vertices;
my @skeleton_lines = ();
foreach my $edge (@{ $voronoi->edges }) {
# ignore lines going to infinite
next if $edge->[1] == -1 || $edge->[2] == -1;
my $line = Slic3r::Line->new($vertices->[$edge->[1]], $vertices->[$edge->[2]]);
next if !$self->contains_line($line);
# contains_point() could be faster, but we need an implementation that
# reliably considers points on boundary
#next if !$self->contains_point(Slic3r::Point->new(@{$vertices->[$edge->[1]]}))
# || !$self->contains_point(Slic3r::Point->new(@{$vertices->[$edge->[2]]}));
push @skeleton_lines, [$edge->[1], $edge->[2]];
}
return () if !@skeleton_lines;
# now walk along the medial axis and build continuos polylines or polygons
my @polylines = ();
{
my @lines = @skeleton_lines;
push @polylines, [ map @$_, shift @lines ];
CYCLE: while (@lines) {
for my $i (0..$#lines) {
if ($lines[$i][0] == $polylines[-1][-1]) {
push @{$polylines[-1]}, $lines[$i][1];
} elsif ($lines[$i][1] == $polylines[-1][-1]) {
push @{$polylines[-1]}, $lines[$i][0];
} elsif ($lines[$i][1] == $polylines[-1][0]) {
unshift @{$polylines[-1]}, $lines[$i][0];
} elsif ($lines[$i][0] == $polylines[-1][0]) {
unshift @{$polylines[-1]}, $lines[$i][1];
} else {
next;
}
splice @lines, $i, 1;
next CYCLE;
}
push @polylines, [ map @$_, shift @lines ];
}
}
my @result = ();
my $simplify_tolerance = $width / 7;
foreach my $polyline (@polylines) {
next unless @$polyline >= 2;
# now replace point indexes with coordinates
my @points = map Slic3r::Point->new(@{$vertices->[$_]}), @$polyline;
if ($points[0]->coincides_with($points[-1])) {
next if @points == 2;
push @result, @{Slic3r::Polygon->new(@points[0..$#points-1])->simplify($simplify_tolerance)};
} else {
push @result, Slic3r::Polyline->new(@points);
$result[-1]->simplify($simplify_tolerance);
}
}
return @result;
}
package Slic3r::ExPolygon::Collection;
use Slic3r::Geometry qw(X1 Y1);

7
lib/Slic3r/Layer/Region.pm
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@ -224,16 +224,17 @@ sub make_perimeters {
# process thin walls by collapsing slices to single passes
if (@thin_walls) {
my @p = map @{$_->medial_axis($pspacing)}, @thin_walls;
if (0) {
use Slic3r::SVG;
require "Slic3r/SVG.pm";
Slic3r::SVG::output(
"medial_axis.svg",
no_arrows => 1,
expolygons => \@thin_walls,
#expolygons => \@thin_walls,
polylines => \@p,
);
exit;
}
my @paths = ();
for my $p (@p) {
next if $p->length <= $pspacing * 2;

119
xs/src/Geometry.cpp
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@ -1,4 +1,6 @@
#include "Geometry.hpp"
#include "Line.hpp"
#include "PolylineCollection.hpp"
#include "clipper.hpp"
#include <algorithm>
#include <map>
@ -94,28 +96,107 @@ MedialAxis::build(Polylines* polylines)
construct_voronoi(this->lines.begin(), this->lines.end(), &this->vd);
// prepare a cache of twin edges to prevent getting the same edge twice
// (Boost.Polygon returns it duplicated in both directions)
std::set<const voronoi_diagram<double>::edge_type*> edge_cache;
// iterate through the diagram by starting from a random edge
this->edge_cache.clear();
for (VD::const_edge_iterator edge = this->vd.edges().begin(); edge != this->vd.edges().end(); ++edge)
this->process_edge(*edge, polylines);
}
void
MedialAxis::process_edge(const VD::edge_type& edge, Polylines* polylines)
{
// if we already visited this edge or its twin skip it
if (this->edge_cache.count(&edge) > 0) return;
// iterate through the diagram
for (voronoi_diagram<double>::const_edge_iterator it = this->vd.edges().begin(); it != this->vd.edges().end(); ++it) {
(void)edge_cache.insert(it->twin());
if (edge_cache.count(&*it) > 0) continue;
if (!it->is_primary()) continue;
Polyline p;
if (!it->is_finite()) {
this->clip_infinite_edge(*it, &p.points);
} else {
p.points.push_back(Point( it->vertex0()->x(), it->vertex0()->y() ));
p.points.push_back(Point( it->vertex1()->x(), it->vertex1()->y() ));
if (it->is_curved()) {
this->sample_curved_edge(*it, &p.points);
// mark this as already visited
(void)this->edge_cache.insert(&edge);
(void)this->edge_cache.insert(edge.twin());
if (this->is_valid_edge(edge)) {
Line line = Line(
Point( edge.vertex0()->x(), edge.vertex0()->y() ),
Point( edge.vertex1()->x(), edge.vertex1()->y() )
);
bool appended = false;
if (!polylines->empty()) {
Polyline &last_p = polylines->back();
if (line.a == last_p.points.back()) {
// if this line starts where last polyline ends, just append the other point
last_p.points.push_back(line.b);
appended = true;
} else if (line.b == last_p.points.back()) {
// if this line ends where last polyline ends, just append the other point
last_p.points.push_back(line.a);
appended = true;
}
}
polylines->push_back(p);
if (polylines->empty() || !appended) {
// start a new polyline
polylines->push_back(Polyline());
Polyline &p = polylines->back();
p.points.push_back(line.a);
p.points.push_back(line.b);
}
}
// look for connected edges (on both sides)
this->process_edge_neighbors(edge, polylines);
this->process_edge_neighbors(*edge.twin(), polylines);
}
void
MedialAxis::process_edge_neighbors(const VD::edge_type& edge, Polylines* polylines)
{
std::vector<const VD::edge_type*> neighbors;
for (const VD::edge_type* neighbor = edge.rot_next(); neighbor != &edge; neighbor = neighbor->rot_next()) {
// skip already seen edges
if (this->edge_cache.count(neighbor) > 0) continue;
// skip edges that we wouldn't include in the MAT anyway
if (!this->is_valid_edge(*neighbor)) continue;
neighbors.push_back(neighbor);
}
// process neighbors recursively
if (neighbors.size() == 1) {
this->process_edge(*neighbors.front(), polylines);
} else if (neighbors.size() > 1) {
// close current polyline and start a new one for each branch
for (std::vector<const VD::edge_type*>::const_iterator neighbor = neighbors.begin(); neighbor != neighbors.end(); ++neighbor) {
Polylines pp;
this->process_edge(**neighbor, &pp);
polylines->insert(polylines->end(), pp.begin(), pp.end());
}
}
}
bool
MedialAxis::is_valid_edge(const VD::edge_type& edge) const
{
// if we only process segments representing closed loops, none if the
// infinite edges (if any) would be part of our MAT anyway
if (edge.is_secondary() || edge.is_infinite()) return false;
/* If the cells sharing this edge have a common vertex, we're not interested
in this edge. Why? Because it means that the edge lies on the bisector of
two contiguous input lines and it was included in the Voronoi graph because
it's the locus of centers of circles tangent to both vertices. Due to the
"thin" nature of our input, these edges will be very short and not part of
our wanted output. The best way would be to just filter out the edges that
are not the locus of the maximally inscribed disks (requirement of MAT)
but I don't know how to do it. Maybe we could check the relative angle of
the two segments (we are only interested in facing segments). */
const voronoi_diagram<double>::cell_type &cell1 = *edge.cell();
const voronoi_diagram<double>::cell_type &cell2 = *edge.twin()->cell();
if (cell1.contains_segment() && cell2.contains_segment()) {
Line segment1 = this->retrieve_segment(cell1);
Line segment2 = this->retrieve_segment(cell2);
if (segment1.a == segment2.b || segment1.b == segment2.a) return false;
}
return true;
}
void
@ -203,7 +284,7 @@ MedialAxis::retrieve_point(const voronoi_diagram<double>::cell_type& cell)
}
Line
MedialAxis::retrieve_segment(const voronoi_diagram<double>::cell_type& cell)
MedialAxis::retrieve_segment(const voronoi_diagram<double>::cell_type& cell) const
{
voronoi_diagram<double>::cell_type::source_index_type index = cell.source_index() - this->points.size();
return this->lines[index];

10
xs/src/Geometry.hpp
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@ -3,6 +3,7 @@
#include "BoundingBox.hpp"
#include "Polygon.hpp"
#include "Polyline.hpp"
#include "boost/polygon/voronoi.hpp"
using boost::polygon::voronoi_builder;
@ -20,14 +21,19 @@ class MedialAxis {
Points points;
Lines lines;
void build(Polylines* polylines);
void process_edge(const voronoi_diagram<double>::edge_type& edge, Polylines* polylines);
void process_edge_neighbors(const voronoi_diagram<double>::edge_type& edge, Polylines* polylines);
bool is_valid_edge(const voronoi_diagram<double>::edge_type& edge) const;
void clip_infinite_edge(const voronoi_diagram<double>::edge_type& edge, Points* clipped_edge);
void sample_curved_edge(const voronoi_diagram<double>::edge_type& edge, Points* sampled_edge);
Point retrieve_point(const voronoi_diagram<double>::cell_type& cell);
Line retrieve_segment(const voronoi_diagram<double>::cell_type& cell);
Line retrieve_segment(const voronoi_diagram<double>::cell_type& cell) const;
private:
voronoi_diagram<double> vd;
typedef voronoi_diagram<double> VD;
VD vd;
BoundingBox bb;
std::set<const VD::edge_type*> edge_cache;
};
} }

4
xs/src/PolylineCollection.hpp
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@ -10,8 +10,8 @@ class PolylineCollection
{
public:
Polylines polylines;
PolylineCollection* chained_path(bool no_reverse) const;
PolylineCollection* chained_path_from(const Point* start_near, bool no_reverse) const;
PolylineCollection* chained_path(bool no_reverse = false) const;
PolylineCollection* chained_path_from(const Point* start_near, bool no_reverse = false) const;
Point* leftmost_point() const;
};

6
xs/src/TriangleMesh.cpp
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@ -580,10 +580,10 @@ TriangleMesh::slice(const std::vector<double> &z, std::vector<ExPolygons>* layer
#ifdef SLIC3R_DEBUG
size_t holes_count = 0;
for (ExPolygons::const_iterator e = ex_slices.begin(); e != ex_slices.end(); ++e) {
holes_count += e->holes.count();
holes_count += e->holes.size();
}
printf("Layer %d (slice_z = %.2f): %d surface(s) having %d holes detected from %d polylines\n",
layer_id, z[layer_id], ex_slices.count(), holes_count, loops->count());
printf("Layer %zu (slice_z = %.2f): %zu surface(s) having %zu holes detected from %zu polylines\n",
layer_id, z[layer_id], ex_slices.size(), holes_count, loops->size());
#endif
ExPolygons* layer = &(*layers)[layer_id];