Re: [frogs] Changing subproperties with grob-set-property (working on bug #40)

[Marc Hohl <marc@xxxxxxxxxx>]

Neil Puttock schrieb:
> 2009/10/31 Marc Hohl <marc@xxxxxxxxxx>:
>
>   
> > The syntax
> >
> > (ly:grob-set-property! grob '(bound-details right X) right-X)
> >
> > won't work, however. How can I put the new value into the list?
> >     
>
> You'll have to do some C++ hacking.  There are two options here (see
> the code in grob-scheme.cc):
>
> 1) amend ly_grob_set_property_x () to allow lists
>
> 2) create a new exported function ly_grob_set_nested_property_x ()
>
> I favour the latter, since it's cleaner to implement: if you amend
> ly:grob-set-property! you'll have to use a hybrid type check, since
> the property path could be either a symbol or list.
>   
Ok, I will have a look at the code. I am sure that questions will arise,
because c++ is new for me, but nevertheless ...
>   
> > Or is my approach aiming in the wrong direction?
> >     
>
> I think it's fine for a tweak, but a better fix would involve working
> directly on the code in line-spanner.cc.
>   
Hm, probably.
>               (set! right-X (- right-X 30)))
>
> You could get a compensatory value automatically by using
> ly:grob-extent on the accidental.
>   
Yes, the value was simply a quick test to see whether
my approach will work as I expected, but I didn't work
on the grob-extent, because ly:grob-set-property! failed.

> Whatever you decide to do, allowing nested properties in
> ly:grob-set-property! would be a useful enhancement.
>   
So I concentrate on this, try to solve it and afterwards come back to 
the initial
problem. If I follow proposal 2, there will be a 
ly:grob-set-nested-property!
function, am I right?

Thanks for your reply!

Marc
> Regards,
> Neil
>
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