Re: Start, end, gradient of Glissando

[Thomas Morley]

Am So., 24. Okt. 2021 um 01:18 Uhr schrieb Aaron Hill
<lilypond@hillvisions.com>:
>
> On 2021-10-23 5:17 am, Thomas Morley wrote:
> > Any hints?
>
> normalized-endpoints
>
> Your Y-left and Y-right are the extreme values that have not been
> interpolated using the values from normalized-endpoints.  Borrowing
> logic from Line_spanner::print, here is a modification to your test
> code:
>
> %%%%
>             (normalized-endpoints (ly:grob-property grob
> 'normalized-endpoints))
>             (Y-length (- Y-right Y-left))
>             (normal-Y-left (+ Y-left (* (car normalized-endpoints)
> Y-length)))
>             (normal-Y-right (- Y-right (* (- 1 (cdr
> normalized-endpoints)) Y-length)))
>             (start-coord
>               (cons
>                 (- X-left grob-relative-coord (- left-padding) (/ thick
> 2))
>                 (+ normal-Y-left left-padding-y)))
>             (end-coord
>               (cons
>                 (- X-right grob-relative-coord right-padding (- (/ thick
> 2)))
>                 (- normal-Y-right right-padding-y current-y-coord))))
> %%%%
>
>
> -- Aaron Hill

Hi Aaron,

this does the trick for the vertical values.

Though, how could I have found it myself?
My lack of C++-knowledge hinders me to understand the "logic from
Line_spanner::print". I usually learn things from looking at
scheme-codings.
But there is none in our source using 'normalized-endpoints, apart
from setting it in some grob-definitions.
The description reads: "Represents left and right placement over the
_total_ spanner, where the _width_ of the spanner is normalized
between 0 and 1."
I think the wording is misleading, at least "total" means the unbroken
spanner for me, thus I never considered to look at it for broken
spanners.
The word "width" means the extent in X-axis direction, again no reason
to look at it for extents in Y-axis.

Probably the whole description should be rewritten.

Many thanks!
  Harm

P.S.
While the Y-values are fixed now, I found some flaw, if left/right
padding is not zero. At least for broken or cross-staff Glissando.
I'll continue research..., unless someone has another hint?