[poppler] Patch proposal: Implementation for real gouraud shaded triangles

Christian Feuersaenger cfeuersaenger at googlemail.com
Wed Oct 6 01:11:17 PDT 2010

Am 05.10.2010 22:59, schrieb Albert Astals Cid:
> A Dijous, 30 de setembre de 2010, Christian Feuersaenger va escriure:
>> Hello Albert,
>> Am 30.09.2010 00:00, schrieb Albert Astals Cid:
>>> A Dijous, 19 d'agost de 2010, vàreu escriure:
>>>> Dear Albert,
>>>> attached you find a test.pdf in which the improvements can be seen.
>>>> The rendering quality of my patch is much better; it eliminates the
>>>> moire effects of the flat shading approximation (top left image).
>>>> Compare also the image with opacity on page 2 of test.pdf.
>>>> Besides the improved rendering quality, the most obvious change is the
>>>> required runtime: on my system, the default xpdf requires 15 seconds
>>>> until it stops rendering the first page whereas xpdf with poppler
>>>> support and my new patch requires about one second. The pdftoppm utility
>>>> is also considerably faster.
>>>> Let me stress that the patch is unrelated to my previous bugfixes, so
>>>> rendering problems are only fixed together with the other bugfix.
>>> I'm not sure i understand this last sentence, you say that the patches
>>> are
>>> unrelated but then you say the bugs are only fixed together with the
>>> other
>>> patch?
>>> Should i run a regression test over this patch or does it need to be in
>>> conjunction with the other patch?
>> The "Implementation for real gouraud shaded triangles" is more a new
>> feature than simply a bugfix: it re-implements the shaders for the
>> splash device. Its purpose is mainly a vastly improved rendering speed.
>> I'd suggest to run regression tests on this implementation separately
>> from my other patch proposals.
>> The other patch proposals (you have  processed them already; I still
>> have to investigate your problem report) are bug fixes which should be
>> tested separately.
>> My last remark is to be understood as follows:
>> 1. if you view test.pdf with both patches, you have best quality and
>> highest speed.
>> 2. if you view test.pdf only with the given patch, you have high speed
>> and good quality for the triangle patches, but the coons patch things
>> will be buggy.
>> 3. if you only process the other patch proposal (the bugfixes which are
>> not part of mail), the coons patches are rendered correctly; but the
>> triangle patches are slow and only approximately correct due to the
>> piecewise flat triangle approximation as it is currently done in
>> libpoppler.
>> I think the most reliable quality verification can be gained by testing
>> both patches separately.
> Ok, i've ran the test regression over this aptch and everything seems to be
> ok, could you please fix the FIXME and TODO you have in the code?

Hello Albert,

I'm glad the regression tests passed. Concerning the FIXME and TODO 
list: They constitute (without exception) additional features which do 
not limit the application of the patch (falling back to the old 
implementations automatically). I am willing to work on the FIXMEs, but 
a realization might not be finished before the beginning of the new year 
due to my personal time schedule for the next months.

I suggest to incorporate the patch into libpoppler as-is, and I will 
work on the remaining feature requests eventually.

Best regards


> Thanks,
>    Albert
>> Best regards
>> Christian
>> PS
>> Sorry if you get notifications because of 'Post by non-member to a
>> members-only list'... I keep clicking onto the wrong email address :(
>> (have now registered both of them)
>>> Albert
>>>> Best regards
>>>> Christian
>>>> Am 18.08.2010 23:15, schrieb Albert Astals Cid:
>>>>> A Dijous, 15 de juliol de 2010, Christian Feuersaenger va escriure:
>>>>>> Dear poppler developers,
>>>>>> hereby I propose a new patch for a high quality, fast gouraud
>>>>>> shader for
>>>>>> triangle shadings.
>>>>>> The patch provides
>>>>>> - scalable triangle shadings (in contrast to the old approach),
>>>>>> - correct shading, no approximation using flat triangles,
>>>>>> - greatly (!) improved rendering speed,
>>>>>> - support for opacity (in contrast to the previous approach).
>>>>>> This patch is relative to the master branch,
>>>>>> git show poppler-0.14.0-91-g31ac578 .
>>>>>> It is unrelated to my previous patch proposals concerning shadings;
>>>>>> the
>>>>>> other patch proposal (my mail several weeks ago) is still important
>>>>>> and
>>>>>> relevant. The patch in this mail is independent and does not
>>>>>> include my
>>>>>> previous patch proposals.
>>>>>> I tested the new patch with pdftoppm and with the xpdf-poppler fork of
>>>>>> Rogerio Brito; it appears to work reliable. I tested
>>>>>> - matrix shadings and triangle patch shadings (Types 4 and 5),
>>>>>> - degenerated triangles,
>>>>>> - clipping,
>>>>>> - opacity,
>>>>>> - RGB color spaces.
>>>>>> The implementation now supports these shadings on a display driver
>>>>>> level
>>>>>> and is implemented directly in the splash device (using scanline
>>>>>> sweeps).
>>>>>> I've been defensive: I have no test cases for other color spaces and I
>>>>>> have no test data for non-parametric shadings. Consequently, I
>>>>>> disabled
>>>>>> the shader for these cases; it will fall back to the existing
>>>>>> solutions
>>>>>> (approximate shading by means of many flat triangles).
>>>>>> I hope you find my patch proposal useful. I believe it is worthy of
>>>>>> being part of libpoppler.
>>>>> Do you have a pdf where we can see the improvement this patch gives?
>>>>> Albert
>>>>>> Thanks,
>>>>>> Christian
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