Problem with detecting bridge direction

[ledvinap]

There is probem in _detect_bridge_direction in 1.1.0 (https://github.com/alexrj/Slic3r/blob/master/lib/Slic3r/Layer/Region.pm#L414):

my @clipped = @{intersection_pl([ map $_->split_at_first_point, @$grown ], [$lower->contour])};
# If the split_at_first_point() call above happens to split the polygon inside the clipping area
# we would get two consecutive polylines instead of a single one, so we use this ugly hack to 
# recombine them back into a single one in order to trigger the @edges == 2 logic below.

This assumption is not satisfied - clipper removes overlapping point even for path that is not closed, so one segment is missing in clipped polyline. Recombination test then fails and bridge direction is calculated incorrectly in same cases.

Here is possible test to illustrate issue (using pylyclip.t hollow rectangle expolygon):

    {
    my $intersection = intersection_pl([Slic3r::Polyline->new([110,110], [120,110], [120,120], [110,120], [110,110])], \@$expolygon);
    is $intersection->[0]->length, Slic3r::Polyline->new([110,110], [120,110], [120,120], [110,120], [110,110])->length,
            'line start and end can overlap';
    }

This object triggers problem (on both U bridges): http://www.thingiverse.com/thing:24238, here is my config: https://drive.google.com/file/d/0B9HM4UOKDQBLVW91ZGZON0pCclk (any config should work)

git rev-parse HEAD git rev-parse HEAD
017158c

[alranel]

Thank you very much for the diagnosis.