Scheme function to draw lines based on grob layout

Scheme function to draw lines based on grob layout

A number of C++ stencil callbacks use Line_interface::line to draw
lines based on line-interface properties defining a particular grob.
This allows control of aspects such as line style (based on the setting
of Grob.style) and fine-tuning of dashed lines through dash-fraction
and dash-period.

This patch gives access to Line_interface::line in Scheme through the
callback ly:line-interface::line.  (The simpler name ly:line was ruled
out in an effort to distinguish it from other functions such as
ly:bracket and ly:circle which do not take a grob argument.)  Users
will be able to create custom stencils with more functionality
(including rewriting certain C++ callbacks--such as Hairpin::print--to
allow for easy modifications without loss of capability.)

[david.nalesnik, 2015-08-26 17:39:55]

Please review.  Thanks!

Here's a usage example:

\version "2.19.26"

{
  \override Hairpin.stencil =
  #(lambda (grob)
    (let* ((refp (ly:grob-system grob))
           (bound-L (ly:spanner-bound grob LEFT))
           (bound-R (ly:spanner-bound grob RIGHT))
           (ext-L (ly:grob-extent bound-L refp X))
           (ext-R (ly:grob-extent bound-R refp X))
           (me-X (ly:grob-relative-coordinate grob refp X)))
    (ly:stencil-translate-axis
      (ly:line-interface::line
        grob (interval-center ext-L) 0 (interval-center ext-R) 0)
      (- me-X)
      X)))
  \override Hairpin.to-barline = ##f
  \once\override Hairpin.style = #'dashed-line
  \once\override Hairpin.dash-period = 2
  \once\override Hairpin.dash-fraction = 0.5
  c''1\<
  c''1\!
  \once\override Hairpin.style = #'zigzag
  \once\override Hairpin.zigzag-width = 1.5
  \once\override Hairpin.zigzag-length = 1.5
  \once\override Hairpin.thickness = 2
  c''1\<
  c''1\!
}

[pkx166h, 2015-08-27 07:56:09]

Passes make, make check and a full make doc.

PATCH_REVIEW

[pkx166h, 2015-08-29 07:47:04]

Patch on countdown for Sept 2nd

PATCH_COUNTDOWN

[thomasmorley651, 2015-08-29 10:09:19]

Can't review C++ and right now I don't have a good idea, which possibilities are
offered here.

I think it would be helpful to put up an example. Maybe in snippets or changes
or in regtests. What do you think?

[david.nalesnik, 2015-08-29 13:49:29]

On 2015/08/29 10:09:19, thomasmorley651 wrote:
> Can't review C++ and right now I don't have a good idea, which possibilities
are
> offered here.

I hoped that the test example provided in message #1 would give a good idea of
the possibilities :(  

Basically, you can draw a line modified by any of the properties in
line-interface, taken from a grob with that interface.  (So the line can be
customized, like you can make Hairpin and TupletBracket grobs dashed or
whatever.)
 
> 
> I think it would be helpful to put up an example. Maybe in snippets or changes
> or in regtests. What do you think?

Maybe Changes, though it probably would be something super simple like:

{
  \override Hairpin.stencil = #(lambda (grob) (ly:line-interface::line grob 0 0
5 0))
  \override Hairpin.style = #'zigzag
  c''1\<
  c''1\!
}

I don't think that's a place for a more complex example like the one in #1.

As far as a regtest, I don't think so.  This is just making a C++ function
available which has been in use for a long time.

Snippets--possibly, but maybe in another patch?

What do you think?

DN

[thomasmorley651, 2015-08-29 13:57:38]

On 2015/08/29 13:49:29, david.nalesnik wrote:
> On 2015/08/29 10:09:19, thomasmorley651 wrote:
> > Can't review C++ and right now I don't have a good idea, which possibilities
> are
> > offered here.
> 
> I hoped that the test example provided in message #1 would give a good idea of
> the possibilities :(  

Aaargh, I missed this :((
Just noticed James PATCHES-notification and had a quick look in the code, but
not in the already sent messages.
And yes, it gives me an idea.
Sorry for the noise.

> 
> Basically, you can draw a line modified by any of the properties in
> line-interface, taken from a grob with that interface.  (So the line can be
> customized, like you can make Hairpin and TupletBracket grobs dashed or
> whatever.)
>  
> > 
> > I think it would be helpful to put up an example. Maybe in snippets or
changes
> > or in regtests. What do you think?
> 
> Snippets--possibly, but maybe in another patch?

Agreeing with both: in snippets/follow up