Re: [ft-devel] maxp.maxStackElements (e: Freetype-devel Digest, Vol 141, Issue 4)

[Hin-Tak Leung]

Slight correction, s/fpgm/fpgm or cvt/ .

I can get FontVal 2.0 to match the behavior of FontVal 1.0 regarding 
maxStackElements and stack overflow errors, on all the fonts I mentioned below 
- or if you wish, get freetype to match that of MS rasterer's, by taking the 
+32 off, with the following differences:

- I can't see how the MPPEM instruction can overflow in FreeType, but it can 
with the MS rasterer (according to FontVal 1.0 against font-mfizz.ttf ). So it 
looks like that instruction is implemented differently.

- FreeType won't load 'Apple Color Emoji.ttf' at 10pt, and does not overflow at 
40pt.

- FreeType seems to load the cvt twice, so all messages from overflow in cvt 
happens twice. This is annoying, but not IMHO a big issue since well-behaving 
fonts don't get them, and if you as a font designer getting every error message 
twice, it might be stronger incentive to fix it :-).

Given the first issue - that some instructions are implemented differently - it 
is probably wise that one should add a few on top just to allow one's font to 
work on different rasterers... (assuming some rasterer actually take the font's 
value as is, on trust...)

--------------------------------------------
On Sun, 9/10/16, Hin-Tak Leung <address@hidden> wrote:

 Hi Cosimo,
 
 It is 32 extra elements - elements are minimum 16-bit wide?
 FreeType probably use 32-bit int's for it.
 
 I checked my test results of the ~5000 fonts I tested for
 E6045 ( the "open font" part is up at
 http://htl10.users.sourceforge.net/tmp/FontVal-test-results-2016July/
 ) - the FontVal code for stack overflow.
 
 You can do something like
       bzip2 -dc fedora-1.0-texlive.txt.bz2|
 grep E6045
 to extract that entry yourself
 
 Because of the +32,  E6045 is not seen with FontVal 2.0
 at all. (I'll fix it one day...)
 But a few fonts can trigger that with FontVal 1.0. They are
 
 /usr/share/texlive/texmf-dist/fonts/truetype/public/fontmfizz/font-mfizz.ttf
 
 from texlive-fontmfizz-svn35892.0
 
 DecoTypeNaskh.ttf and Apple Color Emoji.ttf from apple
 (various versions)
 
 and a few *-*-hkscs-u.ttf CJK fonts from my private stash.
 
 You can probably play with either the two apple fonts or the
 mfizz font from texlive a bit, move the value up and down a
 bit to see what FontVal 1.0 thinks is the correct answer.
 
 BTW, all of the flagged errors from FontVal 1.0 happens in
 the fpgm! So you need to make sure that you are processing
 fpgm correctly.
 
 I'd be interested if you can say, modify any of those fonts
 to get FontVal 1.0, FontVal 2.0 (taking the +32 into
 account) and VTT into some sort of agreement.
 
 Hin-Tak