[ft-devel] is that a bug in freetype on allowing INSTCTRL to be called from glyphs?

[Hin-Tak Leung]

Hi,

There is a check in the diagnostics patch which detects whether INSTCTRL is 
being called from glyphs (instead of cvt and etc). I added that because there 
are a couple of fonts shipped with windows 8 which violates that (and the older 
FontVal detects...).

There are two blocks of cryptic and even sarcastic(?) comments below that from 
both Infinality and Nikolaus Waxweiler about subpixel hinting which seems to 
suggest clear type fonts violates that intentionally, if I understand the 
comments correctly? (I think the sarcastic(?) comment is left by Nikolaus 
Waxweiler?). Therefore FreeType possibly does not throw an error because there 
are fonts which do that, quite intentionally; and in any case, FreeType ltself 
probably does not need to care whether  INSTCTRL is being called from glyphs or 
cvt.

But is that a generally bad thing to allow - a glyph containing instructions 
that have side effects, and therefore possibly influences how other glyphs 
should be rendered after it is processed?

Hin-Tak

P.S. the two fonts which trigger that check is euphemia.ttf and frank.ttf . 
That code path is only triggered at or below size 6.