[XeTeX] Fonts with unusual (non-1000) upm sizes

[Andrew Moschou]

> Anyway, the problem is really strange, because by analyzing the
> particular font with which I ran into the problem, I really got the
> impression that the units per em "should be" 1000, since most glyphs
> have advance widths around 600 or 700, which seems a clear hint that the
> intended number of units per em is more like 1000 than 2000.  And, as
> reported on the thread on Typophile, the problems seem to go away when I
> edit the font in FontForge and change the units per em number from 2048
> to 1000, without modifying anything else.

I believe the normal units per em number depends on the font format.
Type 1 fonts tend to have 1000, and TrueType fonts tend to have 2048.
There's nothing preventing a designer from choosing an unusual value.
The Revere music font, for example, one of the most elegant music
fonts ever created (the software it was created for is now obsolete,
and sadly, it's very incompatible with the industry standard software
today) has highly unusual 960 units per em (It's the only font I know
that is neither 1000 nor 2048).

Andrew