[Bug 744812] Re: FontConfig/Qt stack choke on Ubuntu Medium font meta-data (No medium in Inkscape and too bold in Qt apps)

[Michał Sawicz]

The above patch alone does not help as the database isn't used directly.
Instead, requests are forwarded to Fontconfig, which is a good thing.

It then maps Qt weights back to FC weights:
http://qt.gitorious.org/qt/qt/blobs/4.8/src/gui/text/qfontdatabase_x11.cpp#line1489

And the mapping looks as follows:
         0.0 => Medium
  0.0 ÷ 36.5 => Light
 36.5 ÷ 56.5 => Medium
 56.6 ÷ 69.0 => DemiBold
 69.0 ÷ 81.0 => Bold
 81.0 ÷  ∞   => Black

An attentive reader will find that there's no Regular there... Which means Qt will _never_ request a Regular font from Fontconfig, so as long as there's anything closer to Medium than Regular (e.g. Medium), it will choose that over Regular. What's more, it defaults to Medium, which seems a common pattern in that code:
http://qt.gitorious.org/qt/qt/blobs/4.8/src/gui/text/qfontdatabase_x11.cpp#line777
http://qt.gitorious.org/qt/qt/blobs/4.8/src/gui/text/qfontdatabase_x11.cpp#line1069
http://qt.gitorious.org/qt/qt/blobs/4.8/src/gui/text/qfontdatabase_x11.cpp#line1078
http://qt.gitorious.org/qt/qt/blobs/4.8/src/gui/text/qfontdatabase_x11.cpp#line1491

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https://bugs.launchpad.net/bugs/744812

Title:
  FontConfig/Qt stack choke on Ubuntu Medium font meta-data (No medium
  in Inkscape and too bold in Qt apps)

Status in Linux Libertine:
  Unknown
Status in Ubuntu Font Family:
  Invalid
Status in “fontconfig” package in Ubuntu:
  Confirmed
Status in “ubuntu-font-family-sources” package in Ubuntu:
  Confirmed
Status in “fontconfig” source package in Natty:
  Confirmed
Status in “ubuntu-font-family-sources” source package in Natty:
  Fix Released
Status in “fontconfig” source package in Oneiric:
  Confirmed
Status in “ubuntu-font-family-sources” source package in Oneiric:
  Fix Released
Status in “fontconfig” source package in Precise:
  Confirmed
Status in “ubuntu-font-family-sources” source package in Precise:
  Fix Released
Status in “fontconfig” source package in Quantal:
  Confirmed
Status in “ubuntu-font-family-sources” source package in Quantal:
  Confirmed

Bug description:
  [Kubuntu natty up-to-date]
  Hi,
  Without any change on my system, I noticed some days ago that my default font (ubuntu) changed. Some odd behaviour appeared : ubuntu medium 10 pt was ok but ubuntu medium 11pt was bold (-> in my taskbar clock or in kpackapgekit). In fact, after some play with kcm kubuntu font manager, the ubuntu medium 10pt was wrong, since kcm module shows the true appearance of ubuntu medium, which is quite bold. I swapped to ubunu light font
  SO ! I changed font hinting to light (default in kubuntu seems to be medium) and it seems to have solved bugs.
  Anyway, "ubuntu font" management by KDE seems to be strange, and firefox 4 font rendering is worse (imho) with light hinting (but maybe because of unselected "system default" parameter in fonts kcm).

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