Re: [ft-devel] gamma correction and stem darkening

[suzuki toshiya]

Dear Derek,

I have not expected that the tricky font detection
technique was still worthful to discus after the
expiration of bytecode interpreter patent :-)

I'm interested in the example which current detection
cannot detect correctly. The current detection is just
a comparison with the checksums of "known" tricky fonts,
and, if there is yet another tricky font, it should be
appended the the blacklist.

Regards,
suzuki toshiya

Derek B. Noonburg wrote:
> On 17 Jan, Werner LEMBERG wrote:
>>> Unfortunately, I don't think it will be possible to detect the
>>> tricky fonts.
>> I think it *is* possible.  The method, as implemented by Toshiya-san,
>> compares various SFNT table checksums.  Among them is the `cvs '
>> table, and modifying this table is essentially impossible without
>> interpreting and changing the bytecode.  Ditto for `fpgm'.  I dare to
>> say that even a subsetted font with a single glyph contains the
>> original `cvs ' and `fpgm' tables unmodified, which should enable
>> FreeType to discover its trickyness.
>>
>> Do you have counterexamples to this assumption?
> 
> Very interesting... I wasn't aware that FreeType used that technique.  I
> just looked through the code and found tt_check_trickyness_sfnt_ids -- I
> assume that's the code you're referring to.  I didn't trace through the
> code; do I need to do anything special to enable those checksum tests?
> 
> I have at least one PDF file with Chinese TrueType fonts that render
> correctly with the native hinter and incorrectly without it.  I'll
> extract those fonts and see what the cvt and fpgm tables look like.
> 
> I'll also be happy to make the fonts available for testing.
> 
> - Derek
> 
> 
> _______________________________________________
> Freetype-devel mailing list
> address@hidden
> https://lists.nongnu.org/mailman/listinfo/freetype-devel