"jr" <cre### [at] gmailcom> wrote:
> ...
> somewhat unrelated, I cannot understand why the difference in Y-axis translates,
> is this a POV-Ray bug?  (attached, thank you)

uh, oh, belay that..  found my thinking cap.  :-)


regards, jr.

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On 3/6/22 08:35, jr wrote:
> if you ever recall why, please tell.  now that I know about it, I do wonder what
> the rationale/potential benefit is when the chunk is not written.

OK. Found my related debugging newsgroup post.

Much more detail on the v3.8/v4.0 sRGB block issue being written nor not 
can be found in a Mar 20, 2021 post to povray.beta-test. "File png/ppm 
gamma issues. v3.8." See:

http://news.povray.org/povray.beta-test/thread/%3C60563168%241%40news.povray.org%3E/

or

Message: <60563168$1@news.povray.org>

The thread started after questions from ingo related to pgm/ppm file 
output. I stumbled across the png sRGB block issue during that work. 
Look for "---  png gamma issue.' for the parts of the original post 
related to png input/output.

The bug amounts to POV-Ray not being consistent with 'itself' with 
respect to png sRGB handling.

Looks like in reading the thread again I never did the detailed work to 
figure out what all changed to cause the sRGB block to be dropped on 
default writes though 'srgb' is our default output/input png gamma 
handling profile.

I'd spent many days understanding what was happening in detail and 
didn't want to spend hours to days more trying to run down the commit(s) 
where the post v3.7 srgb png output file gamma handling broke. I just 
fixed the issue - which explains why I couldn't remember the detailed 
causes(a)!

(a) This time it might not have been my old failing brain! Of course, I 
didn't remember I hadn't dug enough to determine exactly how we got into 
the buggy state... ;-)

I know clipka worked quite a bit on the image file handling code over 
years while working toward v3.71/v3.8(v4.0). It was likely broken 
sometime during those changes.

Aside: Because broken v3.71/v3.8/v4.0 versions do still write a gamma 
2.2 chunk, the differences visually be will be small / hard to 'see' - 
they're at the dark end. This probably why the bug went years not 
getting picked up. It's one of those insidious subtle bugs that cause 
confusing / hair pulling results when they do bite.

Bill P.

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William F Pokorny <ano### [at] anonymousorg> wrote:

> Aside: Because broken v3.71/v3.8/v4.0 versions do still write a gamma
> 2.2 chunk, the differences visually be will be small / hard to 'see' -
> they're at the dark end. This probably why the bug went years not
> getting picked up. It's one of those insidious subtle bugs that cause
> confusing / hair pulling results when they do bite.

Interesting.

Do you think there's a shell command that will output some unique result to
distinguish between the two types of gamma encoded png files?

If there is, maybe someone can demonstrate how to run a pre-parse/render command
to write that to a file, and then have a macro parse that and set the png read
parameters to properly/consistently adapt to however any given file is written?
(perhaps sending a message to the debug stream to ID which gamma type the file
is...)

I see that as being the best workaround for the time being.

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hi,

William F Pokorny <ano### [at] anonymousorg> wrote:
> On 3/6/22 08:35, jr wrote:
> > if you ever recall why, ...
>
> OK. Found my related debugging newsgroup post.
>
> Much more detail on the v3.8/v4.0 sRGB block issue being written nor not
> can be found in a Mar 20, 2021 post to povray.beta-test. "File png/ppm
> gamma issues. v3.8." See:
> [snip]

thanks (very much).  so recent, yet, I've no memory of reading the thread.  :-(

> ...
> Aside: Because broken v3.71/v3.8/v4.0 versions do still write a gamma
> 2.2 chunk, the differences visually be will be small / hard to 'see' -
> they're at the dark end. This probably why the bug went years not
> getting picked up. It's one of those insidious subtle bugs that cause
> confusing / hair pulling results when they do bite.

guessing that you "look closer" than I do.  also, I "misuse" gamma perhaps,
mixing sRGB light_source and rgb[ft] colours routinely, bad either the result is
ok-ish or my eyes are not up to it (anymore) :-).


regards, jr.

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hi,

William F Pokorny <ano### [at] anonymousorg> wrote:
> ... It's one of those insidious subtle bugs that cause
> confusing / hair pulling results when they do bite.

may have run into one those with 'povr' yesterday.  been using it while playing
with the USaF (see p.b.a) code since it's quicker to render.  all ok for the 500
frame tests, but when I went to do a "final" render, it crashed
("uncategorized", from memory) at the 3048th frame.  (sorry, bearer of bad news
and all that)


regards, jr.

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On 3/13/22 04:34, jr wrote:
> hi,
> 
> William F Pokorny <ano### [at] anonymousorg> wrote:
>> ... It's one of those insidious subtle bugs that cause
>> confusing / hair pulling results when they do bite.
> 
> may have run into one those with 'povr' yesterday.  been using it while playing
> with the USaF (see p.b.a) code since it's quicker to render.  all ok for the 500
> frame tests, but when I went to do a "final" render, it crashed
> ("uncategorized", from memory) at the 3048th frame.  (sorry, bearer of bad news
> and all that)
> 
> 
> regards, jr.
> 

This with the Real_Time_Capture=true|false (+-rtc) capability for the 
real time rendering mode (.pfm output) or with traditional animation?

Is the fail easily repeatable?

Bill P.

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hi,

William F Pokorny <ano### [at] anonymousorg> wrote:
> This with the Real_Time_Capture=true|false (+-rtc) capability for the
> real time rendering mode (.pfm output) or with traditional animation?

regular animation, running from an ini.


> Is the fail easily repeatable?

not sure, happened late in the animation[*], had no stomach to try + repeat,
sorry.  the code in question is the 'usaf' animation posted same time (March
13th).

[*] as I wrote, I was v surprised because 'povr' run the (shorter) test segments
without hassle, and fast.


regards, jr.

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On 3/17/22 02:04, jr wrote:
>> Is the fail easily repeatable?
> not sure, happened late in the animation[*], had no stomach to try + repeat,
> sorry.  the code in question is the 'usaf' animation posted same time (March
> 13th).

No problem. The flaky issues / bugs are always the hard ones to run down.

Did you continue the animation successfully starting from frame 3048?
Or, is it an animation where each frame depends on information from 
previous frames(s) such that starting at frame 3048 not possible?

I might try running valgrind looking for memory leaks with your 
particular animation as a shot in the dark. But, that's not something 
I'll get to for a while.

Wondering too if the regular animation mechanisms can develop the memory 
bubbles seen with RTR. My guess is the frame rates with regular 
animation always too slow for it to happen - and as a light user of 
regular animation I've never noticed a (povms) memory bubble effect but, 
never gone looking for it, so who knows.

Bill P.

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hi,

William F Pokorny <ano### [at] anonymousorg> wrote:
> On 3/17/22 02:04, jr wrote:
> >> Is the fail easily repeatable?
> > not sure, ...
> No problem. The flaky issues / bugs are always the hard ones to run down.

took copy of code posted + tried again, several times, every time the run (now)
crashes at frame 2800; have tried to remember which if any changes I made, but
can only think of quality + dimensions in ini file.  attached excerpt from
'povr' build-log, libraries in use, and the animation state at the time.



> Did you continue the animation successfully starting from frame 3048?
> Or, is it an animation where each frame depends on information from
> previous frames(s) such that starting at frame 3048 not possible?

no, did not.  simply switched to POV-Ray proper, wanted "it" (the anim) out of
my hair :-).


> I might try running valgrind looking for memory leaks with your
> particular animation as a shot in the dark. But, that's not something
> I'll get to for a while.

running with 480x360 and aa threshold .3 should do.


> Wondering too if the regular animation mechanisms can develop the memory
> bubbles seen with RTR. My guess is the frame rates with regular
> animation always too slow for it to happen - and as a light user of
> regular animation I've never noticed a (povms) memory bubble effect but,
> never gone looking for it, so who knows.

sorry, no ideas at all.  (it's as if the 'tmp_' dictionary is not updated in
time for next access)


regards, jr.

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Attachments:
Download 'frame_2800.txt' (4 KB)

On 3/17/22 11:19, jr wrote:
> Degenerate cylinder, base point = apex point.
> Fatal error in parser: Uncategorized error.
> Render failed

The three lines above come from a test during parsing while additional 
internal data for the cone/cylinder is being done using a function 
within cone.cpp. The tests is finding that the base and apex are <1e-10 
(a) apart - and throwing an error rather than issuing a parse error via 
message(b). The same code exists in POV-Ray proper v3.7 onward and povr 
(c).

(a) - The cone code hasn't been reworked as yet in povr to remove 
'EPSILON' use. The test value there should be ~4.4e-8 or povr's 
gkMinIsectDepthReturned. FWIW.

(b) - The particular test could be done completely inside the parser I 
think. Not sure why it's done in the cone/cylinder shape code.

(c) - There has long been a TODO note in the code suggesting that 
particular throw should be a 'possible error' instead - with execution 
continuing. I don't agree with the TODO note. Where base and apex are 
too close, it's an error in cone/cylinder specification.

---
The puzzle for me at the moment is I have no idea why those parsed base 
and apex vectors would be different between any versions of POV-Ray.

Best guess. It's due some indirect difference where I've moved to 
'double' from 'float' in povr and the previous 'snap' of the vector 
components to floats rounded length 'up' in a way not tripping the 
throw. In other words, values previously rounded such that the base to 
apex length is 'long enough'.

Bill P.

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