Re: Imprecise font scaling

[Jean Abou Samra]

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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