I've (somewhat) successfully created a FretDiagrams context, with a
Fret_diagram_engraver. I can sort of make things work. Now I'd like
some clarification on Items.
As part of the engraver, I have the code
fret_diagram_ = make_item ("FretDiagram",SCM_EOL); //WHAT GOES HERE?
It appears to me that the "name" of the Item, FretDiagram, is in fact a
pointer into scm/define-grobs.scm. Since I want to make a FretDiagram
Item, I believe I need to make an alist entry for FretDiagram in
scm/define-grobs.scm. Is there any documentation for what goes in the
alist entry?
Also, as part of making the item, I need to have a "cause", which is
SCM_EOL in this particular example. It appears from some of the
internal documentation that the cause is a music expression, generally
the one responsible for creating the Item/Grob. What is the cause used
for?
Also, what is the difference between an Item and a Grob? From some
earlier descriptions, I think that an Item is one type of Grob; that is,
all Items are Grobs, but not all Grobs are Items (i.e. some Grobs can be
Spanners, etc.). Is this correct?
Thanks,
Carl
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