[poppler] Toward to JBIG2 support in CairoOutputDev

suzuki toshiya mpsuzuki at hiroshima-u.ac.jp
Mon Jan 12 18:56:36 PST 2015 

Dear Albert,

I draw 2 slides about the background of the patch:
http://gyvern.ipc.hiroshima-u.ac.jp/~mpsuzuki/JBIG2/Slide1.GIF
http://gyvern.ipc.hiroshima-u.ac.jp/~mpsuzuki/JBIG2/Slide2.GIF
I hope it helps your understanding.

Regards,
mpsuzuki

Adrian Johnson wrote:
> On 13/01/15 05:40, Albert Astals Cid wrote:
>> El Dilluns, 12 de gener de 2015, a les 21:44:22, Adrian Johnson va escriure:
>>> The latest patch looks good. I'll wait a week before committing to see
>>> if anyone else has any comments. This will give me time to do some
>>> testing of the patch.
>> Can you guys explain what the patch is for? Export? Or so that it's cairo the 
>> one rendering JBig2 and not poppler? Or?
> 
> It allows cairo backends to embed a JBIG2 image instead of uncompressing
> the image and recompressing with Flate. CairoOutputDev already does this
> for jpeg and jpeg2000 images. JBIG2 is a bit more complicated because it
> has global data that can be shared by multiple images. Currently the
> only cairo backend that supports JBIG2 embedding is the pdf output. So
> this patch allows "pdftocairo -pdf" and evince print output which uses
> pdf for printing to keep JBIG2 images in JBIG2 format.
> 
>> Cheers,
>>   Albert
>>
>>> On 11/01/15 23:05, suzuki toshiya wrote:
>>>> Dear Adrian,
>>>>
>>>> OK - considering that there is a lag to the day that Linux
>>>> distribution ship the poppler stable branch including
>>>> CairoOutputDev with JBIG2 support even if I support some
>>>> snapshot of Cairo in current development branch of poppler
>>>> (and there would be no need to support Cairo snapshot in
>>>> the day), I decided to follow original version checking.
>>>>
>>>> Also I removed the default value (NULL) for Ref object to
>>>> JBIG2Stream constructor and removed NULL pointer checking
>>>> in JBIG2Stream constructor (as same as the argument to pass
>>>> Globals object).
>>>>
>>>> I replaced "st" in CairoOutputDev, by "status".
>>>>
>>>> Here I attached revised patch - oh, I'm quite sorry, my
>>>> previous posts were misunderstanding this year as 2014.
>>>>
>>>> Regards,
>>>> mpsuzuki
>>>>
>>>> Adrian Johnson wrote:
>>>>> On 08/01/15 13:35, suzuki toshiya wrote:
>>>>>> Dear Adrian,
>>>>>>
>>>>>> Great Thank you for prompt review! I attached the revised patch,
>>>>>> but please let me discuss a few points.
>>>>>>
>>>>>> Adrian Johnson wrote:
>>>>>>> On 07/01/15 02:58, suzuki toshiya wrote:
>>>>>>>> Hi all,
>>>>>>>>
>>>>>>>> Here I submit a preliminary patch for git head,
>>>>>>>> which enables JBIG2 embedding to PDF surface via Cairo.
>>>>>>> +static cairo_status_t setJBIG2GlobalsIdByRefNums(int refNum, int
>>>>>>> refGen,
>>>>>>> +                                                 cairo_surface_t
>>>>>>> *image)
>>>>>>> +{
>>>>>>> +  GooString *globalsStrId;
>>>>>>> +  char *idBuffer;
>>>>>>> +  cairo_status_t st;
>>>>>>> +
>>>>>>> +
>>>>>>> +  globalsStrId = new GooString;
>>>>>>> +  globalsStrId->appendf("{0:d}-{1:d}", refNum, refGen);
>>>>>>> +  idBuffer = copyString(globalsStrId->getCString());
>>>>>>> +  st = cairo_surface_set_mime_data (image,
>>>>>>> CAIRO_MIME_TYPE_JBIG2_GLOBAL_ID,
>>>>>>>
>>>>>>> The cairo JBIG2 mime types are new to 1.14.0 so will need to be
>>>>>>> inside a
>>>>>>> #if CAIRO_VERSION >= CAIRO_VERSION_ENCODE(1, 14, 0).
>>>>>> If it's acceptable, I want to use the conditional like
>>>>>>
>>>>>>     #ifdef CAIRO_MIME_TYPE_JBIG2_GLOBAL_ID
>>>>>>
>>>>>> The official release of cairo including JBIG2 support is 1.14.0,
>>>>>> however, some distributions use a snapshot before 1.14 which
>>>>>> supports JBIG2. For example, Ubuntu 14.04 (long time support)
>>>>>> ships with 1.13.0~20140204.
>>>>>>
>>>>>> http://packages.ubuntu.com/search?suite=trusty&section=all&arch=any&keyw
>>>>>> ords=libcairo2&searchon=names
>>>>>>
>>>>>>
>>>>>> It includes JBIG2 support. Thus I prefer checking by the JBIG2
>>>>>> macros, instead of the version checking.
>>>>> I'm not keen on making an exception for this case. The target audience
>>>>> for this is very small. It would only help users that compile a new
>>>>> version of poppler on an old distribution without also recompiling
>>>>> cairo. JBIG2 support for pdftocairo is a very minor feature that not
>>>>> many people would be using (so far no one else has requested this
>>>>> feature).
>>>>>
>>>>> If you really want to support distributions using a cairo 1.13 snapshot
>>>>> I suggest adding a comment before the first occurrence of
>>>>> #ifdef CAIRO_MIME_TYPE_JBIG2_GLOBAL_ID to explain why the version macro
>>>>> is not used. Also include
>>>>> "#if CAIRO_VERSION >= CAIRO_VERSION_ENCODE(1, 14, 0)" in the comment so
>>>>> that:
>>>>> a) searching for CAIRO_VERSION will find it, and
>>>>> b) to document that JBIG2 support is in 1.14 or later.
>>>>>
>>>>>> BTW, when the string for UNIQUE_ID is constructed, its syntax
>>>>>> is RefGen-RefNum. In PDF data, RefNum then RefGen is popular
>>>>>> syntax. Is there any reason why the order is reverted?
>>>>> No reason. Feel free to change it to num-gen order.
>>>>>
>>>>>>> +GBool CairoOutputDev::setMimeDataForJBIG2Globals(Stream  *str,
>>>>>>> +                                                 cairo_surface_t
>>>>>>> *image)
>>>>>>> +{
>>>>>>> +  JBIG2Stream *jbig2Str = static_cast<JBIG2Stream *>(str);
>>>>>>> +  Object* globalsStr = jbig2Str->getGlobalsStream();
>>>>>>> +  char *globalsBuffer;
>>>>>>> +  int globalsLength;
>>>>>>> +
>>>>>>> +  // According to PDF spec, Globals should be stream (or nothing)
>>>>>>> +
>>>>>>> +  if (globalsStr->isNull())
>>>>>>> +    return gTrue;
>>>>>>> +
>>>>>>> +  if (!globalsStr->isStream())
>>>>>>> +    return gFalse;
>>>>>>> +
>>>>>>> +  // See JBIG2Stream constructor for valid reference number
>>>>>>> +  if (!jbig2Str->getGlobalsStreamRefNum())
>>>>>>> +    return gFalse;
>>>>>>>
>>>>>>> The globalsStr->isStream() check should be sufficient. The reference
>>>>>>> number should always be valid of the global stream is valid.
>>>>>> Umm. Requesting "both of JBIG2Stream::globalsStream and Ref to
>>>>>> it must be always valid as far as GlobalsStream is used" is
>>>>>> intuitive solution, but public JBIG2Stream constructor has not
>>>>>> requested the Ref to GlobalsStream before in earlier version.
>>>>>>
>>>>>> If some developers use JBIG2Stream constructor with valid
>>>>>> GlobalsStream but without Ref to it (as the syntax before my
>>>>>> patch), there is the situation that JBIG2Stream::globalsStream
>>>>>> is valid but Ref to it is invalid (if I supply the default
>>>>>> value for the argument to pass Ref). How do we detect or prevent
>>>>>> such case?
>>>>>>
>>>>>> A) Supplying the default value (NULL pointer) in the argument
>>>>>> to pass the Ref, and JBIG2Stream returns an error when
>>>>>> globalsStream is valid stream but its Ref is not passed - and
>>>>>> prevent the case that globalsStream is valid but its Ref is
>>>>>> invalid.
>>>>>>
>>>>>> B) Not supplying the default value, and prevent the construction
>>>>>> without the Ref to the globalsStream.
>>>>>>
>>>>>> C) Add new boolean value in JBIG2Stream class, to indicate if
>>>>>> Ref to globalsStream is explicitly set.
>>>>>>
>>>>>> D) Initialize Ref with irregular value (e.g. 0,0 or 0,65535)
>>>>>> internally when Ref is not passed, and deal the case as Ref to
>>>>>> the globalsStream is not initialized (my last patch design)
>>>>>>
>>>>>> Which is the best? Or, no need to case such case?
>>>>> JBIG2Stream is not part of the public API so there is no need to
>>>>> preserve compatibility.
>>>>>
>>>>> Something else I just noticed - could you rename "st" to "status".
>>>>> CairoOutputdev.cc always uses the name "status" for cairo status so we
>>>>> should be consistent with this convention.
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