Re: Imprecise font scaling

[Jean Abou Samra]

Sorry, my mail client changed the formatting in a way I didn't expect.
Resending.

> I'm running the following code
> 
> \version "2.25.12"
> \markup { LOL }
> \markup { \magnify #2.0 LOL }
> 
> and the results are not really precise. When producing --eps, the relevant
> output lines are
> 
> /C059-Roman 3.86523438 output-scale div selectfont
> /C059-Roman 7.73242188 output-scale div selectfont
> 
> However, 2 * 3.86523438 = 7.73046876 != 7.73242188. Basically the same
> behaviour
> can be observed when using Cairo (both for EPS and SVG).
> (Producing SVG without Cairo is pretty disastrous in this regard, but
> that doesn't bother me too much at the moment.)


I'm quite sure this is because of


     int pango_size = static_cast<int> (
        std::lround (static_cast<Real> (requested_size) * PANGO_SCALE));


in lily/font-select.cc, which we cannot really do anything about, because
the Pango API

https://docs.gtk.org/Pango/method.FontDescription.set_size.html

expects an integer size scaled by PANGO_SCALE, which is 1024. That is, we are
limited to a precision of 1/1024 points on the font size.

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