Both QTextLine::naturalTextWidth() and QTextLine::horizontalAdvance()
return the same value for \fint. However, examining esint10.ttf with
fontforge does not reveal any issue with the metrics. The fact that
\fint seems to be the only affected symbol might be due to its code
point, which corresponds to a space, so that maybe Qt makes some
assumptions on the metrics.
As QTextLine::naturalTextWidth() returns the width of the line that is
occupied by text, in the case of a single symbol we can obtain the
same value by using the width of the rectangle bounding the symbol.
Since be836909c52 the positioning of super- and subscripts
for symbol fonts has been broken because the metrics of the
font of the environment (rather than those of the symbol itself)
were used.
There are two techniques that I know of for forcing the direction of a
string, regardlessly of whether its contents is naturally LtR, RtL or
undecided.
1/ The unicode LTR/LTR override characters. This is supposed to be the
clean way, however, it does not seem to work with Qt 5.14 (see
#11691).
2/ The undocumented QTextLayout::setFlags method. This is used
internally and allows to pass the (undocumented) flags
Qt::TextForceRightToLeft and Qt::TextForceLeftToRight. This was
used until we had issues with Qt 5.11 (see #11284).
In order to get the best of both worlds, this patch allows to enable
those two methods separately, and actually enables both at the same
time by default!
(hopefully) Fixes bug #11691.
In particular, the directory frontends/qt4 is renamed to frontends/qt.
Many configurations file have to be updated. All mentions of qt4 in
the source have been audited, and changed to qt if necessary.
The only part that has not been updated is the CMake build system.
