New instrument name positioning in Scheme.

New instrument name positioning in Scheme.

* remove x/y positioning from print callback to separate X- and Y-offset
  callbacks
* add x-offset calculation for system start delimeter extents so all
  instrument names in a system are aligned correctly based on
  self-alignment-X
* use 'when from left-bound instead of get_break_index () to determine
  which text to print; this fixes incorrect indentation and text for
  shortInstrumentName overrides (Issue #452)
* remove acknowledger for system-start-text from
  system-start-delimiter-engraver.cc
* remove system-start-text.cc
* add system-start-text-interface to define-grob-interfaces.scm
* add library functions used by new callbacks to lily-library.scm
  and output-lib.scm

[joeneeman, 2009-07-16 05:52:35]

Just one corner case, otherwise lgtm

http://codereview.appspot.com/91119/diff/1/10
File scm/output-lib.scm (right):

http://codereview.appspot.com/91119/diff/1/10#newcode833
Line 833: (interval-center extent))))
If (not (pair? live-elts)) then (interval-center extent) will be NaN, instead of
0 which would be more sensible.

[Neil Puttock, 2009-07-16 22:51:26]

On 2009/07/16 05:52:35, joeneeman wrote:
> Just one corner case, otherwise lgtm

Thanks, Joe.

I'll add a convert-ly rule for ly:system-start-text::print, a regtest and NEWS
entry before pushing.
 
> 
> http://codereview.appspot.com/91119/diff/1/10
> File scm/output-lib.scm (right):
> 
> http://codereview.appspot.com/91119/diff/1/10#newcode833
> Line 833: (interval-center extent))))
> If (not (pair? live-elts)) then (interval-center extent) will be NaN, instead
of
> 0 which would be more sensible.

That's caught by interval-center, since it returns 0.0 for empty intervals.