Volume rewritten from Perl to C++,

generation of vertex arrays from paths rewritten from Perl to C++,
parallelized.

xs/lib/Slic3r/XS.pm

@@ -247,7 +247,11 @@ sub new {
     );
 }
 
-package Slic3r::GUI::_3DScene::GLVertexArray;
+package Slic3r::GUI::_3DScene::GLVolume::Collection;
+use overload
+    '@{}' => sub { $_[0]->arrayref },
+    'fallback' => 1;
+
 sub CLONE_SKIP { 1 }
 
 package main;
@@ -279,6 +283,7 @@ for my $class (qw(
         Slic3r::Geometry::BoundingBox
         Slic3r::Geometry::BoundingBoxf
         Slic3r::Geometry::BoundingBoxf3
+        Slic3r::GUI::_3DScene::GLVolume
         Slic3r::Layer
         Slic3r::Layer::Region
         Slic3r::Layer::Support