Let horizontal-line be a straight-cut line rather than having rounded edges

Let horizontal-line be a straight-cut line rather than having rounded edges

This actually should just affect staff lines and have them cut off
rather than rounded at their ends.  They merge better into bar lines
that way.  Since there is no support in the backends for lines with
cut edges as such, we use round-filled-box instead (with a rounding
diameter of 0).

Should combine well with issue 2658

[thomasmorley65, 2013-04-11 23:44:03]

Can't review C++ -code, though, from description, I do not understand the reason
for it.

Well, ofcourse it will merge better with barlines, but can you give an example
where the problem isn't solvable with at most medium effort?
Ah, wait, I just found 
http://lsr.dsi.unimi.it/LSR/Search?q=color
Regarding it with very high zoom shows a greater disadvantage of draw-line.
Nevertheless, I think it's more a problem of said snippet, worth fixing.

In general, I'd prefer rounded boxes, but with a little blot-diameter.
Though, I might change my mind once I understand the reason behind the patch.

[thomasmorley65, 2013-04-11 23:55:00]

On 2013/04/11 23:44:03, thomasmorley65 wrote:

> Ah, wait, I just found 
> http://lsr.dsi.unimi.it/LSR/Search?q=color
> Regarding it with very high zoom shows a greater disadvantage of draw-line.
> Nevertheless, I think it's more a problem of said snippet, worth fixing.

Sorry, wrong link.
Should be:
http://lsr.dsi.unimi.it/LSR/Item?id=700

[dak, 2013-04-12 05:44:30]

On 2013/04/11 23:44:03, thomasmorley65 wrote:
> Can't review C++ -code, though, from description, I do not understand the
reason
> for it.
> 
> Well, ofcourse it will merge better with barlines, but can you give an example
> where the problem isn't solvable with at most medium effort?
> Ah, wait, I just found 
> http://lsr.dsi.unimi.it/LSR/Search?q=color
> Regarding it with very high zoom shows a greater disadvantage of draw-line.
> Nevertheless, I think it's more a problem of said snippet, worth fixing.
> 
> In general, I'd prefer rounded boxes, but with a little blot-diameter.

There are several reasons.  One reason is that the metrics for horizontal-line
are wrong: \draw-line (the markup command) accounts for the rounded line ends by
including them in the total width.  horizontal-line, using the same image,
doesn't.

Another is that the staff lines with their current setting fail to cooperate
with <URL:http://code.google.com/p/lilypond/issues/detail?id=2658> in typical
viewing situations and normal bar lines.  The reason is that draw-line produces
line ends that are a circle.  Circles in drawing direction color every pixel
that they touch.  The bar line is drawn with the same thickness in perpendicular
direction and now does _not_ color every pixel that it merely touches, but
rather only a number of pixels appropriate for its thickness (on average, half a
pixel less on each side).  So the circular ends tend to stick through the
barlines at low resolution.

Now cutting the horizontal lines off sharp might be overkill but it saves making
a decision about just how much rounding should be needed.  It also corresponds
with the output of a rake, the engraving tool used for staff lines.

Full circle rounding clearly is too much and it does not reflect the output from
actual engraving.  Cut-off engraving also cooperates nicely with the actual
metrics.

Of course, another motivation was again issue 2658: it turns out that at least
with circular line ends on "lineto stroke", Ghostscript does not do the same
kind of stroke adjustment than I now use for rounded rectangles.  As a result,
staff lines tend to look inconsistent with things like bar lines and note stems.
 Using draw_rounded_box accounts for that, even though it would account for it
with different rounding settings as well.