Get context from a Grob

[Carl Sorensen]

After way too much calendar time (I have very little time for working on 
LilyPond -- either development or music) I have come up with an architecture 
that I think will work well with the dot-column problem.

I want to move the dot-column calculation to a Scheme procedure.  This will 
facilitate users creating their own algorithm for allocating dots if they don't 
like either of the two procedures I will provide (one is Gould, the other is 
what was wanted by the lists in our discussion about it).

In order to do this, I need a property that holds the procedure used to format 
the dot column.  When I did a similar thing with fretboards, I made a context 
property and used that for the procedure.  I thought I could do this here.

However, when I'm formatting the dot column, I'm not in an engraver.  I'm in a 
Scheme callback (Dot_column::calc_positioning_done).  As far as I can see, I 
only have a Grob, not a Grob_info available.  So I don't see a way to get a 
pointer to
the context.

Is there any way to get the context from a Grob in C++?

If there isn't a way to do this, I can create a grob property, and use that.  
But I think it would be cleaner to use a context property.

Thanks in advance for any help.

Carl