Comment 42 for bug 744812

I managed to track down the culprit:

http://qt.gitorious.org/qt/qt/blobs/4.8/src/gui/text/qfontdatabase_x11.cpp#line729

The problem is that Qt only supports 5 weights:
http://qt.gitorious.org/qt/qt/blobs/4.8/src/gui/text/qfont.h#line103
  Light = 25,
  Normal = 50,
  DemiBold = 63,
  Bold = 75,
  Black = 87

FontConfig has 11 weights defined:
http://cgit.freedesktop.org/fontconfig/tree/fontconfig/fontconfig.h#n126
  #define FC_WEIGHT_THIN 0
  #define FC_WEIGHT_EXTRALIGHT 40
  #define FC_WEIGHT_ULTRALIGHT FC_WEIGHT_EXTRALIGHT
  #define FC_WEIGHT_LIGHT 50
  #define FC_WEIGHT_BOOK 75
  #define FC_WEIGHT_REGULAR 80
  #define FC_WEIGHT_NORMAL FC_WEIGHT_REGULAR
  #define FC_WEIGHT_MEDIUM 100
  #define FC_WEIGHT_DEMIBOLD 180
  #define FC_WEIGHT_SEMIBOLD FC_WEIGHT_DEMIBOLD
  #define FC_WEIGHT_BOLD 200
  #define FC_WEIGHT_EXTRABOLD 205
  #define FC_WEIGHT_ULTRABOLD FC_WEIGHT_EXTRABOLD
  #define FC_WEIGHT_BLACK 210
  #define FC_WEIGHT_HEAVY FC_WEIGHT_BLACK
  #define FC_WEIGHT_EXTRABLACK 215
  #define FC_WEIGHT_ULTRABLACK FC_WEIGHT_EXTRABLACK

And getFCWeight maps them as follows:
   0 ÷ 75 => Light
  76 ÷ 140 => Normal
 141 ÷ 190 => DemiBold
 191 ÷ 205 => Bold
 206 ÷ ∞ => Black

Because of that both Ubuntu Regular and Medium fall into the same Qt weight - QFont::Normal. Since that operation loses the granularity, there's probably no easy way to distinguish between Normal and Medium later in the process.

Possible solutions:
a) introduce QFont::Medium
b) make FC_WEIGHT_MEDIUM mapped to QFont::DemiBold
c) drop seemingly duplicate fonts

I myself would lean towards solution a), but neither that or b) really fixes anything - if there's duplicates, it becomes non-deterministic in which font will be selected (the last one added? a random one?). Solution c) seems to be the most complete, but then also quite intrusive. We'd have to only leave the one whose fontconfig weight is closest to the respective weight. So from each of the getFCWeight ranges only one font would be selected, closest to what fontconfig says that weight should be.