Re: Line breaking, simple-spacer, etc.

[Joe Neeman]

On Thu, 2010-02-04 at 15:33 -0500, Boris Shingarov wrote:
> I am experimenting with some modifications to the line breaking code,
> and I am stuck trying to understand how some of it works.  So far my
> understanding is that Simple_spacer operates on a vector of Grobs, and
> it is a well-known Constrained-QP problem (rods = constraints, springs
> = quadratic function to minimize).  What I don't understand is, if the
> spacer operates at the level of Grobs, which are built at an earlier
> stage in the pipeline, how are the changes necessitated by differences
> in line breaking, taken into account?  in other words, if I take the
> last measure of a line and place it on the next line, it is not just a
> matter of literally moving that graphic to where the start of the next
> line is, but I also need to draw a clef, key signature, and possibly
> other fundamental things -- but at that stage in the rendering
> pipeline, is it not too late??

We create lots of extra grobs (eg. a BarNumber at every bar line) but
most of them are not drawn. See the break-visibility property in
item-interface.

Cheers,
Joe