[isabelle] Isabelle2019-RC0: Improved "Isabelle DejaVu" font collection, suitable for text and GUI

Dear Isabelle users,

the Isabelle2019-RC0/ANNOUNCE file says:

* Improved "Isabelle DejaVu" font collection, suitable for text and GUI.

* Update to current Java 11 and Poly/ML 5.8 with better scalability.

To clarify this, here are the corresponding NEWS items:

*** General ***

* The font collection "Isabelle DejaVu" is systematically derived from
the existing "DejaVu" fonts, with variants "Sans Mono", "Sans", "Serif"
and styles "Normal", "Bold", "Italic/Oblique", "Bold-Italic/Oblique".
The DejaVu base fonts are retricted to well-defined Unicode ranges and
augmented by special Isabelle symbols, taken from the former
"IsabelleText" font (which is no longer provided separately). The line
metrics and overall rendering quality is closer to original DejaVu.
INCOMPATIBILITY with display configuration expecting the old
"IsabelleText" font: use e.g. "Isabelle DejaVu Sans Mono" instead.

* The Isabelle fonts render "\<inverse>" properly as superscript "-1".

*** Isabelle/jEdit Prover IDE ***

* Fonts for the text area, gutter, GUI elements etc. use the "Isabelle
DejaVu" collection by default, which provides uniform rendering quality
with the usual Isabelle symbols. Line spacing no longer needs to be
adjusted: properties for the old IsabelleText font had "Global Options /
Text Area / Extra vertical line spacing (in pixels): -2", now it
defaults to 0.

* OpenJDK 11 has quite different font rendering, with better glyph
shapes and improved sub-pixel anti-aliasing. In some situations results
might be *worse* than Oracle Java 8, though.

*** System ***

* Update to OpenJDK 11: the current long-term support version of Java.

(There is actually a small mistake above: the line-spacing default is
now 1 instead of 0.)

The change to OpenJDK 11 --- after Java 8 has been officially declared
at "end-of-live" in Jan-2019 --- follows the normal routine of phasing
out old technologies. Moreover, Java 8 had already shown its old age in
Isabelle applications on high-end hardware: it is very inefficient on
machines with many cores (20-80), and does not quite work with
quasi-containers (e.g. Docker). Java 11 solves these and other problems.
It even provides better font rendering, but that requires proper HiDPI
displays (which are commonplace today).

Nonetheless, very nostalgic users may still do their own private
tinkering to return to Java 8 -- even with the old "IsabelleText" font
with its various flaws. I will not support this, though. Big companies
normally provide expensive support plans for continued support of legacy
technologies, but I am not doing this.


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