Re: NoteHead X-offset, conflict with ly:grob-relative-coordinate

[Paul Morris]

On Dec 11, 2012, at 3:32 PM, Colin Hall <address@hidden> wrote:

> On Tue, Dec 11, 2012 at 04:32:57AM +0000, Keith OHara wrote:
>> Colin Hall <colinghall <at> gmail.com> writes:
>> 
>>> I'm going to post a link to this on the dev forum and see if we can
>>> identify what the bug is, and then I can create a tracker.
>>> 
>> I don't see any bug; reasoning is on -devel.
> 
> That's great, Keith, thanks.
> 
> Paul, here's a link to Keith's explanation on the lilypond-devel
> mailing list archive:
> 
> http://lists.gnu.org/archive/html/lilypond-devel/2012-12/msg00116.html
> 
> I believe Thomas gave you some ideas of how to obtain the engraving
> you wanted.
> 
> OK?

Hi Colin, 

Ok, as Keith is saying, if this is how it is supposed to work then I guess it 
shouldn't be considered a bug.  And luckily there's another way to get the same 
results (thanks to Thomas for that tip).  

I guess that means that a NoteHead's X-offset has not been designed to be a 
property that can be reliably overridden.  I wonder if it would be worth 
documenting this somehow, to keep people from trying to go down this path in 
the future.  

Currently the internals page for NoteHead[1] makes it sound like X-offset is 
simply a number that you can easily override:

  X-offset (number):
  ly:note-head::stem-x-shift
  The horizontal amount that this object is moved relative to its X-parent.

but apparently something more complicated is going on, involving the other 
notes in a chord, and the function for determining their placement.

Anyway, documenting this somehow would be my suggestion, but I don't have the 
knowledge to do it, and I realize that there may be higher priorities, so take 
it FWIW.

On a related note, I just added a snippet for this to the LSR[2] that uses 
ly:grob-translate-axis! instead of X-offset, and I could add a comment to it 
saying that overriding a NoteHead's X-offset does not always work, and to use 
ly:grob-translate-axis! instead.  

(The snippet is not currently working in the LSR, but it works fine for me on 
2.16, so I am guessing that there is a compatibility problem with 2.14.)

Thanks,
-Paul

[1] http://www.lilypond.org/doc/v2.16/Documentation/internals/notehead
[2] http://lsr.dsi.unimi.it/LSR/Item?u=1&id=861