Rendering of fixed-width fonts

[Adrian Robert]

I recently posted about how the Art backend renders the supposedly 
fixed-width "VeraSansMono-Roman" in a non-fixed width way.  For 
reference, here is the shot of size 12 showing a regular grid rendering 
on the bottom:

The problem is not, apparently Art's; if you run FreeType's own 
rendering test (I think called 'ftstring' or something like that), the 
result is the same as the top row above.  Digging further, [NSFont 
-widthOfString] reports that 'm' in size 12 is width of 6.0 while all 
other characters are 7.0.  (Super-simple test program attached.)  This 
information comes from the "advancement" info in the font.  At 
different sizes, other characters besides 'm' are the "odd ones out".

So now to the questions.

First, I can't find any reference to this on the web.  Is everyone 
rendering this font character-by-character manually?  Leaving the 
question of what's happening in Gnome/Gtk aside, if I render in GNUstep 
using a call to DPSmoveto() followed by DPSshow() for every character, 
the problem goes away.  It looks like this is what Terminal.app does.  
Surprisingly, on Art this is actually reasonably fast, but on Xlib 
performance is unacceptable.

This leads to the next question -- is it possible to detect at runtime 
whether you are running under Art or Xlib?  (So as to change rendering 
strategies.)

Is there any more efficient way to render with regular spacing than 
repeated calls to moveto and show?

Sllightly OT, there are no DPS commands on OS X, right?  You have to 
use the Quartz functions, which all start with "CG"?  (The API does not 
look as clean as DPS, but hopefully it grows on one?)

Finally, does anyone have an opinion on whether a fixed-width font 
should have different advancements like VeraSansMono?  Is this a bug in 
the font?  None of the fonts I've tried under Xlib have the problem, 
and FreeMono under Art lacks the problem.  I haven't seen the issue 
with any fonts on OS X.  But the Vera fonts are supposed to be good, 
and look nice, so why does the monospace one have this problem?

testFontWidth.m
Description: Binary data

thanks,
Adrian