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

[suzuki toshiya]

Oh, the mail server of my office was too lazy,
this message was delivered after the commit by
Werner :-)

Regards,
mpsuzuki

suzuki toshiya wrote:
> Dear Derek,
> 
> Thank you very very much for finding new tricky font!
> I will commit your patch soon.
> 
> Regards,
> mpsuzuki
> 
> Derek B. Noonburg wrote:
>> After some more investigation, this appears to be a simple case of a
>> different version (or modification?) of a known tricky font.
>>
>> There are three font subsets in that PDF file.  All three have the same
>> cvt, fpgm, and prep checksums.  The cvt and prep checksums match
>> DFKaiShu, but the fpgm checksum and length are different.
>>
>> I'm attaching those three fonts.
>>
>> And here's a patch:
>>
>> *** freetype-2.6.2/src/truetype/ttobjs.c     2015-11-28 10:08:52.000000000 
>> -0800
>> --- freetype-2.6.2b/src/truetype/ttobjs.c    2016-01-18 11:15:37.982092742 
>> -0800
>> ***************
>> *** 246,252 ****
>>     tt_check_trickyness_sfnt_ids( TT_Face  face )
>>     {
>>   #define TRICK_SFNT_IDS_PER_FACE   3
>> ! #define TRICK_SFNT_IDS_NUM_FACES  17
>>   
>>       static const tt_sfnt_id_rec sfnt_id[TRICK_SFNT_IDS_NUM_FACES]
>>                                          [TRICK_SFNT_IDS_PER_FACE] = {
>> --- 246,252 ----
>>     tt_check_trickyness_sfnt_ids( TT_Face  face )
>>     {
>>   #define TRICK_SFNT_IDS_PER_FACE   3
>> ! #define TRICK_SFNT_IDS_NUM_FACES  18
>>   
>>       static const tt_sfnt_id_rec sfnt_id[TRICK_SFNT_IDS_NUM_FACES]
>>                                          [TRICK_SFNT_IDS_PER_FACE] = {
>> ***************
>> *** 270,275 ****
>> --- 270,280 ----
>>           { 0x5A30CA3BUL, 0x00009063UL }, /* fpgm */
>>           { 0x13A42602UL, 0x0000007EUL }  /* prep */
>>         },
>> +       { /* DFKaiShu2 */
>> +         { 0x11E5EAD4UL, 0x00000350UL }, /* cvt  */
>> +         { 0xA6E78C01UL, 0x00008998UL }, /* fpgm */
>> +         { 0x13A42602UL, 0x0000007EUL }  /* prep */
>> +       },
>>         { /* HuaTianKaiTi */
>>           { 0xFFFBFFFCUL, 0x00000008UL }, /* cvt  */
>>           { 0x9C9E48B8UL, 0x0000BEA2UL }, /* fpgm */
>>
>> - Derek
>>
>>
>> On 2016 Jan 17, suzuki toshiya wrote:
>>> 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
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>>>> https://lists.nongnu.org/mailman/listinfo/freetype-devel
> 
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