Because the font matrix can't be inverted. Pango report: http://bugzilla.gnome.org/show_bug.cgi?id=431990 I wrote about it before here: http://lists.freedesktop.org/archives/cairo/2007-June/010737.html
Fixed now: commit 5dfe47a3f14ee8597395dc53ff57fd429e9804cd Author: Behdad Esfahbod <behdad@behdad.org> Date: Fri Jan 25 00:35:11 2008 -0500 [cairo-scaled-font] Unbreak it after my recent commit Sigh. commit efd3a965244305a069ec231b7ec28cff8d6c67c8 Author: Behdad Esfahbod <behdad@behdad.org> Date: Thu Jan 24 23:35:06 2008 -0500 [cairo-scaled-font] Don't err on font size 0, really First, seems like we were rejecting degenerate font matrix right away at the constructor. Don't do that. Next, PS/PDF were inverting the font scale matrix, assuming that it's invertible. We now keep the inverse too, so they can use it. For the case of a size 0 font, both the scale matrix and its invert are set to 0,0,0,0. That's safe, even if slightly inconsistent. commit 45f269e33020d8d7cf247926712b9c64c1fb8959 Author: Behdad Esfahbod <behdad@behdad.org> Date: Thu Jan 24 22:39:28 2008 -0500 [cairo-scaled-font] Oops, return err if not handling it commit 6d0dc3e0760e6bc6b0eceab48674410b4e865287 Author: Behdad Esfahbod <behdad@behdad.org> Date: Thu Jan 24 22:24:23 2008 -0500 [cairo-scaled-font] Don't err on font size 0
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