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 -- Sent from: http://lilypond.1069038.n5.nabble.com/User-f3.html _______________________________________________ lilypond-user mailing list lilypond-user@gnu.org https://lists.gnu.org/mailman/listinfo/lilypond-user
