Fix regression causing thin walls to come out as zigzag paths. #1573 #1575

lib/Slic3r/ExPolygon.pm

@@ -249,9 +249,11 @@ sub _medial_axis_voronoi {
         } else {
             push @result, Slic3r::Polyline->new(@points);
         }
-        $result[-1]->simplify($width / 7);
     }
     
+    # apply Douglas-Peucker to straighten paths
+    @result = map $_->simplify($width / 7), @result;
+    
     return @result;
 }
 

lib/Slic3r/Layer/Region.pm

@@ -298,8 +298,7 @@ sub make_perimeters {
     # append perimeters
     $self->perimeters->append(@loops);
     
-    # detect thin walls by offsetting slices by half extrusion inwards
-    # and add them as perimeters
+    # process thin walls by collapsing slices to single passes
     if (@thin_walls) {
         my @p = map $_->medial_axis($pspacing), @thin_walls;
         my @paths = ();