+void
+System::build_skylines ()
+{
+ vector<Box> boxes;
+ for (vsize i = 0; i < all_elements_->size (); i++)
+ {
+ Grob *g = all_elements_->grob (i);
+ if (!unsmob_stencil (g->get_property ("stencil")))
+ continue;
+
+ Interval xiv = g->extent (this, X_AXIS);
+ Interval yiv = g->extent (this, Y_AXIS);
+ if (!xiv.is_empty () && !yiv.is_empty ())
+ boxes.push_back (Box (xiv, yiv));
+ }
+
+ SCM horizon_padding_scm = get_property ("skyline-horizontal-padding");
+ Real horizon_padding = robust_scm2double (horizon_padding_scm, 0);
+ skylines_[UP] = Skyline (boxes, horizon_padding, X_AXIS, UP);
+ skylines_[DOWN] = Skyline (boxes, horizon_padding, X_AXIS, DOWN);
+}