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

[Thomas Morley]

2012/12/12 Paul Morris <address@hidden>:
> 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.

Well, quoting

NR 5.5.1 Aligning objects:

Note: Many objects have special positioning considerations which cause
any setting of X-offset or Y-offset to be ignored or modified, even
though the object supports the self-alignment-interface. Overriding
the X-offset or Y-offset properties to a fixed value causes the
respective self-alignment property to be disregarded.

http://lilypond.org/doc/v2.17/Documentation/notation/aligning-objects

But I found no hint about it in the IR

>
> 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.)

Will have a look at it.

>
> 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
>
>
>
>
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-Harm