Improvements to bridge angle detection: use coverage test for all cases (including two-sided bridges and C-shaped bridges) and check for all angles equal to directions of bridge sides

lib/Slic3r/Layer/BridgeDetector.pm

@@ -55,36 +55,37 @@ sub detect_angle {
     my @edges = @{$self->_edges};
     my $anchors = $self->_anchors;
     
-    if (@edges == 2) {
-        my @chords = map Slic3r::Line->new($_->[0], $_->[-1]), @edges;
-        my @midpoints = map $_->midpoint, @chords;
-        my $line_between_midpoints = Slic3r::Line->new(@midpoints);
-        $self->angle($line_between_midpoints->direction);
-    } elsif (@edges == 1 && !$edges[0][0]->coincides_with($edges[0][-1])) {
-        # Don't use this logic if $edges[0] is actually a closed loop
-        # TODO: this case includes both U-shaped bridges and plain overhangs;
-        # we need a trapezoidation algorithm to detect the actual bridged area
-        # and separate it from the overhang area.
-        # in the mean time, we're treating as overhangs all cases where
-        # our supporting edge is a straight line
-        if (@{$edges[0]} > 2) {
-            my $line = Slic3r::Line->new($edges[0]->[0], $edges[0]->[-1]);
-            $self->angle($line->direction);
+    if (!@$anchors) {
+        $self->angle(undef);
+        return undef;
     }
-    } elsif (@edges) {
+    
     # Outset the bridge expolygon by half the amount we used for detecting anchors;
     # we'll use this one to clip our test lines and be sure that their endpoints
     # are inside the anchors and not on their contours leading to false negatives.
     my $clip_area = $self->expolygon->offset_ex(+$self->extrusion_width/2);
     
-        if (@$anchors) {
     # we'll now try several directions using a rudimentary visibility check:
     # bridge in several directions and then sum the length of lines having both
     # endpoints within anchors
+    
+    # we test angles according to configured resolution
+    my @angles = map { $_*$self->resolution } 0..(PI/$self->resolution);
+    
+    # we also test angles of each bridge contour
+    push @angles, map $_->direction, map @{$_->lines}, @{$self->expolygon};
+    
+    # we also test angles of each open supporting edge
+    # (this finds the optimal angle for C-shaped supports)
+    push @angles, map Slic3r::Line->new($_->first_point, $_->last_point)->direction,
+        grep { !$_->first_point->coincides_with($_->last_point) }
+        @edges;
+    
     my %directions_coverage     = ();  # angle => score
     my %directions_avg_length   = ();  # angle => score
     my $line_increment = $self->extrusion_width;
-            for (my $angle = 0; $angle < PI; $angle += $self->resolution) {
+    my %unique_angles = map { $_ => 1 } @angles;
+    for my $angle (keys %unique_angles) {
         my $my_clip_area    = [ map $_->clone, @$clip_area ];
         my $my_anchors      = [ map $_->clone, @$anchors ];
         
@@ -139,16 +140,12 @@ sub detect_angle {
     } keys %directions_coverage;
     
     $self->angle($sorted_directions[-1]);
-        }
-    }
     
-    if (defined $self->angle) {
     if ($self->angle >= PI) {
         $self->angle($self->angle - PI);
     }
     
     Slic3r::debugf "  Optimal infill angle is %d degrees\n", rad2deg($self->angle);
-    }
     
     return $self->angle;
 }