[Development] System-wide font preferences for monospace font

[Jan Kundrát]

Hi,
it looks like Qt tries to respect the font settings of the underlying platform in many situations, but there's unfortunately no way (AFAIK) to get the user's preference for a monospace font. My use case is to fit well into the user's desktop when showing and writing plaintext e-mails.

I've dug through the Qt's sources and it appears that Qt4 contains some code for parsing the KDE's options (src/gui/kernel/qapplication_x11.cpp). It will read the "font" settings, but not the "fixed" settings. Furthermore, it looks like there's no support for various types of default fonts.

In Qt5, the situation looks a bit better, the qtbase:gui/kernel/qplatformtheme.h contains QPlatformTheme::Font enum with support for multiple fonts to be used in the application menus, labels etc. Unfortunately, the support for a "fixed font" is not there. and in addition to that, this feature does not appear to be visible to the user code as it's a private header.

I've added rather basic support for parsing the settings of KDE ($KDEHOME/share/config/kdeglobals) and Gnome (`gconftool-2 --get /desktop/gnome/interface/monospace_font_name`) font preferences in my application [1]. I think that this might be useful for other users of Qt as well, so I'd like to make it a part of Qt5. I've got a couple questions:

- Do you think this is worth it?
- How shall the user-facing API look like?
- Is the approach taken by my code reasonable (calling `gconftool-2` etc) from the Qt's perspective?
- This is for the dev branch, right?

With kind regards,
Jan

[1] http://quickgit.kde.org/?p=trojita.git&a=blobdiff&h=51a4e5c19de01a953d657b275beb52ce5f06c7b2&hp=d800a4976b690a64673e8dd4227ab3903b7b3cb1&hb=d97e9ac219837133203491bd860e3432cccd62e0&f=src%2FGui%2FUtil.cpp

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