Re: feature-request / doc-actualization (right-margin)

[Michael Käppler]

> This is because line-spacing is done earlier than page-spacing - Lily 
> needs a value for line-width when doing horizontal spacing. Therefore 
> line-width isn't really discarded - but later in page.scm it is 
> overwritten, so you can't see it in the page layout.
> What I wasn't unable to figure out is at which time line-width is 
> calculated if you don't set it explicitly. And, much more confusing, I 
> don't see any procedures in C++ that actually check the line-width. A 
> "grep -R line-width *" isn't very informative.
> Any ideas?
Ok, after a lot of time investigating this I think the problem is the 
following function (paper.scm:212):

(define (set-paper-dimensions m w h)
 "M is a module (i.e. layout->scope_ )"
 (let* ((mm (eval 'mm m)))
   (module-define! m 'paper-width w)
   (module-define! m 'paper-height h)
   (module-define! m 'line-width (- w
                                    (ly:modules-lookup (list m) 
'left-margin (* 10 mm))
                                    (ly:modules-lookup (list m) 
'right-margin (* 10 mm))))
   (module-define! m 'indent (/ w 14))
   (module-define! m 'short-indent 0)
   ;; page layout - what to do with (printer specific!) margin settings?
 ))

The proposal of this function is IMHO to set the line-width to 
(paper-width - 20 mm) if no margins are specified. Then, in 
page.scm:191, the difference between paper-width and line-width is 
divided into two equal parts. That's the default behaviour if you 
specify nothing: left-margin and right-margin set to 10 mm.
But even if you set left-margin and right-margin, the function won't 
work, since there is never a 'left-margin or 'right-margin symbol in the 
module the function is called about. Therefore (ly:modules-lookup) 
returns (* 10 mm) in any case.
You can easily test this: the default line-width is 190 mm in any case, 
what margins you ever specify.

I will try to provide a fix as soon as possible.

Cheers,
Michael