let beam thickness depend on line thickness (fix 3173)

let beam thickness depend on line thickness (fix 3173)

One of LilyPond's design principles is "optical sizing"
(described in Essay, section Engraving details), which means
that as the font-size gets smaller, all elements get relatively
thicker.

Before now beam-thickness was defined as a fraction of
staffSpace, which meant no optical sizing (the thickness of the
beam stayed constant relative to the height of the staff). This
patch changes beam-thickness property to be a pair of numbers
(a . b). The actual thickness is calculated according to the
formula  a * lineThickness + b * staffSpace  (similarly to ledger
line thickness).

[lemzwerg, 2013-02-13 06:33:36]

LGTM, inspite of the compilation error which I can't explain :-)

[dak, 2013-02-14 19:43:00]

https://codereview.appspot.com/7312091/diff/1/scm/define-grob-properties.scm
File scm/define-grob-properties.scm (right):

https://codereview.appspot.com/7312091/diff/1/scm/define-grob-properties.scm#...
scm/define-grob-properties.scm:93: (beam-thickness ,number-pair? "Beam
thickness.  It is the sum
You are confusing "sum" and "pair" in this comment.

[janek, 2013-03-19 13:13:20]

Thanks for reviews.  Before i can continue with this patch, i have to
investigate a possible new way of specifying property values (inspired by David
here http://code.google.com/p/lilypond/issues/detail?id=3173#c5)

best,
JAnek

https://codereview.appspot.com/7312091/diff/1/scm/define-grob-properties.scm
File scm/define-grob-properties.scm (right):

https://codereview.appspot.com/7312091/diff/1/scm/define-grob-properties.scm#...
scm/define-grob-properties.scm:93: (beam-thickness ,number-pair? "Beam
thickness.  It is the sum
On 2013/02/14 19:43:00, dak wrote:
> You are confusing "sum" and "pair" in this comment.

You're right, sorry.  I've copied this from the description of
ledger-line-thickness, so that one needs clarifying as well.