Am Mo., 22. Okt. 2018 um 21:59 Uhr schrieb Torsten Hämmerle <torsten.haemme...@web.de>: > > Hi Harm, > > All these numbers are quite confusing at first glance. And at second and > third glance, too. > But they are nothing but conversion factors to switch units. > And, unfortunately, LilyPond basically uses three concurrent units in > parallel: > > - LilyPond units in staff-spaces > - Pango units in mm > - Typographic units in pt > > > This said, I'll try to derive all the values you have found using the > example of a standard 20-pt-staff with the corresponding standard text font > size of 11pt. > I will use a ridiculous number of decimal places to make it easier to > compare the results to your scheme output. > > As LilyPond is a European program, there are no inches to be seen and we'll > only use mm (millimetres). > Both mm and pt are always absolute units (as printed on the final sheet), > whereas a staff-space (let's call it 1sp) is always relative (depending on > the current staff-size). > > > > pt value: conversion between pt and sp > > The 'pt values are the conversion factor from pt to staff-spaces: > A 5-line 20-pt staff is 4sp high ==> 20pt = 4sp, in other words: > > 1pt = 0.2sp (resp: 'pt = 0.2) > > See? Multiply any value in pt by 'pt and you'll get staff-spaces. > > With a 10-pt staff, we get 'pt = 0.4 so that you have to multiply any > pt-value by 0.4 to get the corresponding value in staff-spaces. The factor > has to be twice as big because a 10pt staff is half the size of a 20pt > staff. > > > ancestor-pt value: conversion between pt and mm > > In markup (i.e. font environment), Pango fonts (metrics and size in mm!) > come into play. > > This factor does not change when varying global-staff-size or anything, > because both pt and mm are absolute units and the conversion factor always > stays the same. Knowing how many mm or pt are in an inch, it's easy to > derive the factor: > 1in = 25.4mm > 1in = 72.27pt > > 1pt = 0.3514598035145980351459803514598 mm > This is your ancestor-pt value. :) > > Our standard 11pt-font therefore will be 3.8660578386605783... mm in size > *Caveat:* the Pango font size from stencil-expr is not quite that, because > there is some rounding applied to avoid buffering too many fonts with with > microscopic size differences. > > > text-font-size: Just the actual font size in pt > > The text-font-size displayed for a 20pt staff is 11pt (as suspected). > When setting global-staff-size to 10pt, text-font-size will consequently > only be half as big: 5.5pt. > > > font and size form stencil-expr > > This is, as usual, the font size in (absolute) mm, but slightly quantized to > avoid the buffering of too many differently-sized fonts with only > microscopic font size differences. > > 3.865234375 is about what we'd expect for a standard 11pt font, applying > \fontsize #2 will change this by a factor of 2^(2/6) = 1.2599210498 so that > we get a > 4.870927651... as reported (slight quanting/rounding effects). > > > output-scale: converting staff-spaces into mm > > Finally, the output-scale factor is needed to transform LilyPond metrics (or > \translate #'(a . b) operations) from staff spaces to Pango mm. > > > In a 20pt standard stave, four staff-spaces will make up the 20pt, i.e. 1sp > = 5pt. > Using the pt-to-mm conversion factor (we want mm for Pango!), one > staff-space is > 1sp = 5pt = 1.7572990175... mm (that's your output-scale). > > If we change the staff-size to 16pt, we get > 1pt = 4pt = 1,4058392... as output-scale. > > > That's about all, I think… > > HTH, > Torsten
Hi Torsten, thanks for all the info, I'll need to study it thoroughly. Btw, I meanwhile got LilyPond 2.8.8 working in an old LilyDev. With this ancient version ly:stencil-fonts always returns '() as well. Thanks, Harm _______________________________________________ lilypond-user mailing list lilypond-user@gnu.org https://lists.gnu.org/mailman/listinfo/lilypond-user
