Re: Inconsistent beam-slope?

[David Kastrup]

Thomas Morley <address@hidden> writes:

> Am Mi., 5. Juni 2019 um 23:56 Uhr schrieb David Kastrup <address@hidden>:
>>
>> Thomas Morley <address@hidden> writes:
>>
>> > while working on automated slashed Beams, I noticed my
>> > stencil-procedure was always inexact for non-horizontal Beams. I
>> > looked at 'X-positions and 'positions of a Beam to get it's slope and
>> > derived the slope from those values.
>> >
>> > But the visible gradient obviously relies on blot-diameter as well.
>> > Look at the attached image (code for it below). There you can always
>> > see three overlayed Beams with blot-diameters: 0, 0.5 and 1
>> > For _identical_ 'positions the _visible_ slope is not the same. And
>> > I've got the impression the difference increases with steeped
>> > beam-slope.
>> >
>> > Is this intended or a bug?
>> >
>> > Thanks,
>> >   Harm
>> >
>> > Here the used code:
>> >
>> > {
>> >   \override Beam.stencil =
>> >     #(lambda (grob)
>> >        (let* ((layout  (ly:grob-layout grob)))
>> >          (ly:stencil-add
>> >            (begin
>> >             (ly:output-def-set-variable! layout 'blot-diameter 1)
>> >              (stencil-with-color (ly:beam::print grob) black))
>> >            (begin
>> >              (ly:output-def-set-variable! layout 'blot-diameter 0.5)
>> >              (stencil-with-color (ly:beam::print grob) red))
>> >            (begin
>> >              (ly:output-def-set-variable! layout 'blot-diameter 0)
>> >              (stencil-with-color (ly:beam::print grob) cyan)))))
>> >
>> >
>> >   \override Beam.positions = #'(2 . 8)
>> >   b8^[ b]
>> >   \override Beam.positions = #'(2 . 7)
>> >   b8^[ b]
>> >   \override Beam.positions = #'(2 . 6)
>> >   b8^[ b]
>> >   \override Beam.positions = #'(2 . 5)
>> >   b8^[ b]
>> >   \override Beam.positions = #'(2 . 4)
>> >   b8^[ b]
>> >   \override Beam.positions = #'(2 . 3)
>> >   b8^[ b]
>> >   \override Beam.positions = #'(2 . 2)
>> >   b8^[ b]
>> > }
>>
>> You talk about beam slope a lot but instead specify beam positions.
>> I get the impression that those positions are heeded pretty well, so
>> I don't see fit to label this as a bug.  What would you think qualifies
>> as problematic here?
>
> I need to know the actual slope of a Beam.
> Probably too naive, but I thought I could go for (pseudocode):
> positions-delta / X-positions-delta
> If this is wrong, I have no good idea how to do it different.
>
> Any hints?

Subtract blot-diameter from X-positions-delta?

-- 
David Kastrup