[isabelle-dev] Isabelle DejaVu against old Isabelle Text font

Makarius makarius at sketis.net
Sun Feb 10 19:47:28 CET 2019

On 08/02/2019 10:03, Christian Sternagel wrote:
> I am glad to hear that others have the same experience, I thought my
> eyes were going bad ;)
> But seriously, "buy a new screen" is not always possible. For example,
> in the upcoming summer term I am teaching an Isabelle class at the
> University of Innsbruck. In my experience (and I just reconfirmed this
> for the room I will be teaching in), the projectors we have here a
> typically rather old (and have low resolution, but that is a different
> story).
> At the moment there is a palpable difference (font rendering crispness
> wise) between using Isabelle2018 with projector (which I will do anyway
> for my class) and some recent development version (sorry I didn't note
> down what changeset I used for testing my setup).

Classic JDK 8 from Oracle and OpenJDK 11 (e.g. from AdoptOpenJDK) are
different in many ways, and it is definitely required to get used to the
new look of font rendering. (For me Isabelle2018 already looks very

With proper parameters -- in software and hardware -- fonts should come
out better than before.

First of all, sub-pixel rendering should be enabled, see this NEWS entry
from Isabelle/f714114b0571 (25-Oct-2018):

  *** Isabelle/jEdit Prover IDE ***

  * Improved sub-pixel font rendering (especially on Linux), thanks to
OpenJDK 11.

(In Java 8, sub-pixel rendering made things worse.)

Since that that NEWS entry is a bit too implicit, I have now changed the
default to enable "Subpixel HRGB" always on all platforms
(Isabelle/f610115ca3d0). I have checked my usual test machines for
Windows and macOS, to see that it all looks fine.

Secondly, I have done some more research on FreeType, the renderer used
for OpenJDK on Linux. It appears that the DejaVu family gets some
special treatment if it shows up under its original name, but not if it
is a renamed copy. So I have fine-tuned the Isabelle DejaVu fonts in
Isabelle/4791988fcbc4 to impose the FreeType auto-hinting beforehand to
the TrueType file: this leads to isabelle_fonts-20190210 in

In summary:

  * Isabelle font rendering should be once again slightly better on Linux.

  * There is a small risk that it has slightly degraded on Windows and

In other words: early adopters should look closely if it is all fine. We
are (very slowly) moving towards the Isabelle2019 release (presumably
June 2019), and everything needs to be beyond doubt when released.


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