New ->scale() method for ExPolygon::XS

xs/src/ExPolygon.hpp

@@ -19,8 +19,24 @@ class ExPolygon
     Polygon contour;
     Polygons holes;
     SV* arrayref();
+    void scale(double factor);
 };
 
+#define scale_polygon(poly, factor) \
+    for (Polygon::iterator pit = (poly).begin(); pit != (poly).end(); ++pit) { \
+        (*pit).x *= factor; \
+        (*pit).y *= factor; \
+    }
+
+void
+ExPolygon::scale(double factor)
+{
+    scale_polygon(contour, factor);
+    for (Polygons::iterator it = holes.begin(); it != holes.end(); ++it) {
+        scale_polygon(*it, factor);
+    }
+}
+
 void
 perl2polygon(SV* poly_sv, Polygon& poly)
 {

xs/t/04_expolygon.t

@@ -4,7 +4,7 @@ use strict;
 use warnings;
 
 use Slic3r::XS;
-use Test::More tests => 5;
+use Test::More tests => 6;
 
 my $square = [  # ccw
     [100, 100],
@@ -30,4 +30,10 @@ my $clone = $expolygon->clone;
 is_deeply [ @$clone ], [$square, $hole_in_square], 'clone';
 # TODO: check that modifying the clone doesn't modify the original one
 
+$expolygon->scale(1.5);
+is_deeply [ @$expolygon ], [
+    [map [ 1.5*$_->[0], 1.5*$_->[1] ], @$square],
+    [map [ 1.5*$_->[0], 1.5*$_->[1] ], @$hole_in_square]
+    ], 'scale';
+
 __END__

xs/xsp/ExPolygon.xsp

@@ -8,6 +8,7 @@
 %name{Slic3r::ExPolygon::XS} class ExPolygon {
     %name{_clone} ExPolygon(ExPolygon& self);
     ~ExPolygon();
+    void scale(double factor);
 %{
 
 ExPolygon*