blot diameter warning

[Werner LEMBERG]

[lilypond 2.2.5]


I have done this:

    \context {
      \ScoreContext
      \accepts "Top"
    }

    \context {
      \name "Top"
      \alias "Staff"
      \type "Engraver_group_engraver"
      \consists "Output_property_engraver"
      \consists "Bar_engraver"
      \consists "Font_size_engraver"
      \consists "Skip_event_swallow_translator"
      \consists "Mark_engraver"
      \consists "Script_engraver"
      \consists "Text_engraver"
      \consists "Axis_group_engraver"

      minimumVerticalExtent = #'(0 . 4)
    }

to create a new context `Top' which produces an invisible staff at the
top of an orchestral score for rehearsal marks and tempo indications
(like `Allegro').

Without including the Bar_engraver, rehearsal marks are sometimes not
aligned exactly on the bar (e.g., if the bar line is preceded by a
small clef), so I use

      \override BarLine #'transparent = ##t

later on.

Doing this gives a nasty (but harmless) error:

  programming error: round filled box vertical extent smaller than
                     blot; decreasing blot

Reason is that I haven't included a Staff_symbol_engraver; it seems to
me that the call to Lookup::round_filled_box in
Bar_line::simple_barline (file bar-line.cc) doesn't work as expected.

If my analysis is correct, I suggest to call Lookup:round_filled_box
only if the bar line is visible -- maybe there are other, similar
situations in the lilypond code.

Note that adding a Staff_symbol_engraver with making the staff
invisible later on doesn't give a correct layout.


    Werner