diff --git a/lib/Slic3r/GUI/Plater.pm b/lib/Slic3r/GUI/Plater.pm
index dd5929ad..0b850ac6 100644
--- a/lib/Slic3r/GUI/Plater.pm
+++ b/lib/Slic3r/GUI/Plater.pm
@@ -1270,7 +1270,7 @@ sub _trigger_model_object {
 	    
     	my $mesh = $model_object->mesh;
     	$mesh->repair;
-        $self->convex_hull(Slic3r::Polygon->new(@{Math::ConvexHull::MonotoneChain::convex_hull($mesh->used_vertices)}));
+        $self->convex_hull(Slic3r::Polygon->new(@{Math::ConvexHull::MonotoneChain::convex_hull($mesh->vertices)}));
 	    $self->facets(scalar @{$mesh->facets});
 	    $self->vertices(scalar @{$mesh->vertices});
 	    
diff --git a/lib/Slic3r/Geometry.pm b/lib/Slic3r/Geometry.pm
index abe00f20..6e77e9b4 100644
--- a/lib/Slic3r/Geometry.pm
+++ b/lib/Slic3r/Geometry.pm
@@ -5,7 +5,7 @@ use warnings;
 require Exporter;
 our @ISA = qw(Exporter);
 our @EXPORT_OK = qw(
-    PI X Y Z A B X1 Y1 X2 Y2 MIN MAX epsilon slope line_atan lines_parallel 
+    PI X Y Z A B X1 Y1 X2 Y2 Z1 Z2 MIN MAX epsilon slope line_atan lines_parallel 
     line_point_belongs_to_segment points_coincide distance_between_points 
     chained_path_items chained_path_points normalize tan move_points_3D
     line_length midpoint point_in_polygon point_in_segment segment_in_segment
@@ -35,6 +35,8 @@ use constant X1 => 0;
 use constant Y1 => 1;
 use constant X2 => 2;
 use constant Y2 => 3;
+use constant Z1 => 4;
+use constant Z2 => 5;
 use constant MIN => 0;
 use constant MAX => 1;
 our $parallel_degrees_limit = abs(deg2rad(0.1));
diff --git a/lib/Slic3r/Geometry/BoundingBox.pm b/lib/Slic3r/Geometry/BoundingBox.pm
index 67b77da8..27d6fd27 100644
--- a/lib/Slic3r/Geometry/BoundingBox.pm
+++ b/lib/Slic3r/Geometry/BoundingBox.pm
@@ -1,6 +1,8 @@
 package Slic3r::Geometry::BoundingBox;
 use Moo;
-use Slic3r::Geometry qw(X Y Z MIN MAX X1 Y1 X2 Y2);
+
+use List::Util qw(min max);
+use Slic3r::Geometry qw(X Y Z MIN MAX X1 Y1 X2 Y2 Z1 Z2);
 use Storable qw();
 
 has 'extents' => (is => 'ro', required => 1);
@@ -19,6 +21,18 @@ sub new_from_points {
     ]);
 }
 
+# 2D/3D
+sub new_from_bb {
+    my $class = shift;
+    my ($bb) = @_;
+    
+    return $class->new(extents => [
+        [ $bb->[X1], $bb->[X2] ],
+        [ $bb->[Y1], $bb->[Y2] ],
+        (@$bb == 6) ? [ $bb->[Z1], $bb->[Z2] ] : (),
+    ]);
+}
+
 # 3D
 sub new_from_points_3D {
     my $class = shift;
@@ -27,6 +41,24 @@ sub new_from_points_3D {
     return $class->new(extents => [ Slic3r::Geometry::bounding_box_3D($points) ]);
 }
 
+sub merge {
+    my $class = shift;
+    my (@bounding_boxes) = @_;
+    
+    my $self = ref($class)
+        ? $class
+        : shift @bounding_boxes;
+    
+    foreach my $bounding_box (@bounding_boxes) {
+        for my $axis (X .. $#{$self->extents}) {
+            $self->extents->[$axis][MIN] = min($self->extents->[$axis][MIN], $bounding_box->extents->[$axis][MIN]);
+            $self->extents->[$axis][MAX] = max($self->extents->[$axis][MAX], $bounding_box->extents->[$axis][MAX]);
+        }
+    }
+    
+    return $self;
+}
+
 # four-arguments 2D bb
 sub bb {
     my $self = shift;
diff --git a/lib/Slic3r/Model.pm b/lib/Slic3r/Model.pm
index 2052df8b..2be84e22 100644
--- a/lib/Slic3r/Model.pm
+++ b/lib/Slic3r/Model.pm
@@ -159,16 +159,6 @@ sub _arrange {
     }
 }
 
-sub vertices {
-    my $self = shift;
-    return [ map @{$_->vertices}, @{$self->objects} ];
-}
-
-sub used_vertices {
-    my $self = shift;
-    return [ map @{$_->used_vertices}, @{$self->objects} ];
-}
-
 sub size {
     my $self = shift;
     return $self->bounding_box->size;
@@ -178,7 +168,7 @@ sub bounding_box {
     my $self = shift;
     
     if (!defined $self->_bounding_box) {
-        $self->_bounding_box(Slic3r::Geometry::BoundingBox->new_from_points_3D($self->used_vertices));
+        $self->_bounding_box(Slic3r::Geometry::BoundingBox->merge(map $_->bounding_box, @{$self->objects}));
     }
     return $self->_bounding_box;
 }
@@ -352,11 +342,6 @@ sub mesh {
     return $mesh;
 }
 
-sub used_vertices {
-    my $self = shift;
-    return [ map $_->mesh->used_vertices, @{$self->volumes} ];
-}
-
 sub size {
     my $self = shift;
     return $self->bounding_box->size;
@@ -376,8 +361,10 @@ sub bounding_box {
     my $self = shift;
     
     if (!defined $self->_bounding_box) {
-        # TODO: calculate bb in XS
-        $self->_bounding_box(Slic3r::Geometry::BoundingBox->new_from_points_3D(map $_->mesh->vertices, @{$self->volumes}));
+        my @meshes = map $_->mesh, @{$self->volumes};
+        my $bounding_box = Slic3r::Geometry::BoundingBox->new_from_bb((shift @meshes)->bb3);
+        $bounding_box->merge(Slic3r::Geometry::BoundingBox->new_from_bb($_->bb3)) for @meshes;
+        $self->_bounding_box($bounding_box);
     }
     return $self->_bounding_box;
 }
diff --git a/lib/Slic3r/Print.pm b/lib/Slic3r/Print.pm
index dd43a7b3..a8235478 100644
--- a/lib/Slic3r/Print.pm
+++ b/lib/Slic3r/Print.pm
@@ -144,7 +144,7 @@ sub add_model {
         
         # we also align object after transformations so that we only work with positive coordinates
         # and the assumption that bounding_box === size works
-        my $bb = Slic3r::Geometry::BoundingBox->new_from_points_3D([ map @{$_->used_vertices}, grep $_, @meshes ]);
+        my $bb = Slic3r::Geometry::BoundingBox->merge(map $_->bounding_box, grep $_, @meshes);
         my @align2 = map -$bb->extents->[$_][MIN], (X,Y,Z);
         $_->translate(@align2) for grep $_, @meshes;
         
diff --git a/lib/Slic3r/Print/Object.pm b/lib/Slic3r/Print/Object.pm
index 7d1575d6..2519aa8a 100644
--- a/lib/Slic3r/Print/Object.pm
+++ b/lib/Slic3r/Print/Object.pm
@@ -144,15 +144,13 @@ sub slice {
     # process facets
     for my $region_id (0 .. $#{$self->meshes}) {
         my $mesh = $self->meshes->[$region_id] // next;  # ignore undef meshes
+        $mesh->repair;
         
         {
-            my $m = Slic3r::TriangleMesh->new;
-            $m->ReadFromPerl($mesh->vertices, $mesh->facets);
-            $m->repair;
-            my $lines = $m->slice([ map $_->slice_z, @{$self->layers} ]);
-            for my $layer_id (0..$#$lines) {
+            my $loops = $mesh->slice([ map $_->slice_z, @{$self->layers} ]);
+            for my $layer_id (0..$#$loops) {
                 my $layerm = $self->layers->[$layer_id]->regions->[$region_id];
-                $layerm->make_surfaces($lines->[$layer_id]);
+                $layerm->make_surfaces($loops->[$layer_id]);
             }
             # TODO: read slicing_errors
         }
diff --git a/lib/Slic3r/TriangleMesh.pm b/lib/Slic3r/TriangleMesh.pm
index 434b5ada..c0f37137 100644
--- a/lib/Slic3r/TriangleMesh.pm
+++ b/lib/Slic3r/TriangleMesh.pm
@@ -19,11 +19,6 @@ sub center {
     return $self->bounding_box->center;
 }
 
-sub used_vertices {
-    my $self = shift;
-    return $self->vertices;
-}
-
 sub facets_count {
     my $self = shift;
     return $self->stats->{number_of_facets};
@@ -31,7 +26,7 @@ sub facets_count {
 
 sub bounding_box {
     my $self = shift;
-    return Slic3r::Geometry::BoundingBox->new_from_points_3D($self->used_vertices);
+    return Slic3r::Geometry::BoundingBox->new_from_bb($self->bb3);
 }
 
 # this will return *scaled* expolygons, so it is expected to be run
diff --git a/t/print.t b/t/print.t
index 485ad12b..743c06dc 100644
--- a/t/print.t
+++ b/t/print.t
@@ -13,7 +13,7 @@ use Slic3r::Test;
 
 {
     my $print = Slic3r::Test::init_print('20mm_cube', rotation => 45);
-    ok !(first { $_ < 0 } map @$_, map @{$_->used_vertices}, grep $_, map @{$_->meshes}, @{$print->objects}),
+    ok !(first { $_ < 0 } map @$_, map @{$_->vertices}, grep $_, map @{$_->meshes}, @{$print->objects}),
         "object is still in positive coordinate space even after rotation";
 }
 
diff --git a/xs/xsp/TriangleMesh.xsp b/xs/xsp/TriangleMesh.xsp
index df0b827b..b05c9b0f 100644
--- a/xs/xsp/TriangleMesh.xsp
+++ b/xs/xsp/TriangleMesh.xsp
@@ -126,6 +126,18 @@ TriangleMesh::slice(z)
     OUTPUT:
         RETVAL
 
+std::vector<double>
+TriangleMesh::bb3()
+    CODE:
+        RETVAL.push_back(THIS->stl.stats.min.x);
+        RETVAL.push_back(THIS->stl.stats.min.y);
+        RETVAL.push_back(THIS->stl.stats.max.x);
+        RETVAL.push_back(THIS->stl.stats.max.y);
+        RETVAL.push_back(THIS->stl.stats.min.z);
+        RETVAL.push_back(THIS->stl.stats.max.z);
+    OUTPUT:
+        RETVAL
+
 %}
 };