+ std::vector<Real> line_pos = Staff_symbol::line_positions (staff);
+ if (!line_pos.empty ())
+ {
+ std::sort (line_pos.begin (), line_pos.end ());
+ ydim[DOWN] = line_pos.front ();
+ ydim[UP] = line_pos.back ();
+ if (Real const height = ydim.length ())
+ {
+ ydim.widen (-0.25 * height);
+
+ /*
+ ydim has now the required height; to satisfy req. 2
+ find the staff spaces containing current endpoints.
+
+ standard algorithms are suitable to find the upper
+ line of these spaces; we must choose between
+ upper_bound and lower_bound considering that if
+ there's a line exactly at quarter of the staff (the
+ lower end) then we need the space below it, while if
+ there's a line exactly at three quarters of the staff
+ (upper end) then we need the space above it.
+
+ if the middle of the space found is not low/high
+ enough, take the next space (if there are no more
+ spaces, ydim won't be enlarged further).
+ */
+ std::vector<Real>::const_iterator it
+ = std::lower_bound (line_pos.begin (), line_pos.end (),
+ ydim[DOWN]);
+ assert (line_pos.begin () < it);
+ double val = (it[-1] + it[0]) / 2;
+ if (ydim[DOWN] < val && line_pos.begin () < it - 1)
+ val = (it[-2] + it[-1]) / 2;
+ ydim.add_point (val);
+
+ it = std::upper_bound (line_pos.begin (), line_pos.end (),
+ ydim[UP]);
+ assert (it < line_pos.end ());
+ val = (it[-1] + it[0]) / 2;
+ if (val < ydim[UP] && it + 1 < line_pos.end ())
+ val = (it[0] + it[1]) / 2;
+ ydim.add_point (val);
+ }
+ }