Explosia Obj ID problems

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Maui
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Explosia Obj ID problems

Post by Maui » Fri Mar 16, 2018 9:42 am

I have noticed a strange behavior when turning the OBJ ID Pass on. I work on a fire simulation using Explosia and after switching on Object IDs for the Geo the whole scene got brighter by about 1stop. Even after unchecking the OBJ Id pass again it will render brighter than it should. Has anyone else experienced that as well? It seems that after a system newstart it works for the moment (I will continue to observe this)


In addition I found that sometimes a cached Explosia Sim will show up as a solid Box in the Real-Time Preview window. To solve that I have to disable the cache, sim a few frames "live" and after that I can re-enable the cache object.
But more importantly the same "box" seems to block the OBJ ID pass. Here it doesn't matter if it is cached or not. I have attached a screenshot showing the problem. The roof and the wnidows should all be visible in the obj id pass
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OBJ_ID_Explo_problem.png
OBJ_ID_Explo_problem.png (109.98 KiB) Viewed 821 times

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Mohamed Sakr
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Re: Explosia Obj ID problems

Post by Mohamed Sakr » Fri Mar 16, 2018 11:44 am

Maui wrote:
Fri Mar 16, 2018 9:42 am
I have noticed a strange behavior when turning the OBJ ID Pass on. I work on a fire simulation using Explosia and after switching on Object IDs for the Geo the whole scene got brighter by about 1stop. Even after unchecking the OBJ Id pass again it will render brighter than it should. Has anyone else experienced that as well? It seems that after a system newstart it works for the moment (I will continue to observe this)


In addition I found that sometimes a cached Explosia Sim will show up as a solid Box in the Real-Time Preview window. To solve that I have to disable the cache, sim a few frames "live" and after that I can re-enable the cache object.
But more importantly the same "box" seems to block the OBJ ID pass. Here it doesn't matter if it is cached or not. I have attached a screenshot showing the problem. The roof and the wnidows should all be visible in the obj id pass
1- object ID takes the entire volume (so it will appear as a box)
2- the bright problem is due to using multipass, you will need to make sure that you set the output color space to linear from save settings. (by default it is sRGB).

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Maui
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Re: Explosia Obj ID problems

Post by Maui » Fri Mar 16, 2018 12:21 pm

Hey Mohamed
1 - I didn't apply an Obj ID to the Explosia Object just the elements of the house. So it is strange that those parts seem to be blocked by the Explosia Object
2 - it did it randomly. After a restart it looked fine again. Normally I set my colorspace to linear as I tend to render out exrs from C4d

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Maui
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Re: Explosia Obj ID problems

Post by Maui » Thu Mar 22, 2018 12:07 pm

Also if I try to get the Shadow of the sim using the other objects set to Shadow catcher there are unwanted render issues where parts of the image are blocked (in the top part of the attached image you can see that the smoke is blocked until it reaches a certain point)
If I look at the alpha channel it also looks as if the Explosia Object is seen by the shadow catcher.

In general: Explosia doesn't show up in the shadow pass at the moment, Or am I missing something here?
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Shadow Catcher.png
Shadow Catcher.png (300.29 KiB) Viewed 785 times

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Mohamed Sakr
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Re: Explosia Obj ID problems

Post by Mohamed Sakr » Thu Mar 22, 2018 1:39 pm

Maui wrote:
Thu Mar 22, 2018 12:07 pm
Also if I try to get the Shadow of the sim using the other objects set to Shadow catcher there are unwanted render issues where parts of the image are blocked (in the top part of the attached image you can see that the smoke is blocked until it reaches a certain point)
If I look at the alpha channel it also looks as if the Explosia Object is seen by the shadow catcher.

In general: Explosia doesn't show up in the shadow pass at the moment, Or am I missing something here?
I can't understand, it should show (they are just shadows, doesn't matter if it is Explosia or not).
what do you expect, and what is the result?

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Maui
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Re: Explosia Obj ID problems

Post by Maui » Thu Mar 22, 2018 2:46 pm

Hey Mohamed,
In my actual scene I want to comp the fire render over filmed footage. That's why I would need the shadows of the the fire (separately)

I've made a simpler example scene for you to take a look at. If you enable the shadow catcher option on the plane it cuts away everything from the smoke that "overlaps it".
In both situtations (shadow catcher on or off) the shadow pass is emty
I've also set the scene up with some Obj IDs for you take a look at it also does the strange "box-blocking" I've shown in the first post
Thanks
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Fire-Test.zip
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Maui
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Re: Explosia Obj ID problems

Post by Maui » Fri Mar 23, 2018 12:37 pm

As the fire isn't seen in the Object Id pass it makes it extremely complicated to composite the fire onto my footage. There are parts of the fire that live inside the addict and when I hide the house geo those parts are revealed. If I give the house a black material it get's blocked but the house is than in the beauty pass/alpha channel. I would probably have to work with the World Position Pass using the Physcial or Standart Renderer, as a Matte for the entire roof doesn't do the trick here, to get a Matte for it.

Or is there any other way at the moment to block certain elements in the scene as we can do with the Matte Object in the Standart or Physcial Renderer?

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Mohamed Sakr
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Re: Explosia Obj ID problems

Post by Mohamed Sakr » Fri Mar 23, 2018 12:55 pm

Maui wrote:
Fri Mar 23, 2018 12:37 pm
As the fire isn't seen in the Object Id pass it makes it extremely complicated to composite the fire onto my footage. There are parts of the fire that live inside the addict and when I hide the house geo those parts are revealed. If I give the house a black material it get's blocked but the house is than in the beauty pass/alpha channel. I would probably have to work with the World Position Pass using the Physcial or Standart Renderer, as a Matte for the entire roof doesn't do the trick here, to get a Matte for it.

Or is there any other way at the moment to block certain elements in the scene as we can do with the Matte Object in the Standart or Physcial Renderer?
did you try Holdout shader on the house?

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Maui
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Re: Explosia Obj ID problems

Post by Maui » Fri Mar 23, 2018 1:21 pm

Great didn't know about that shader. That does the trick in this case. Thanks a lot 8-)

But the problem with the shadow catchers, shadow pass and Obj Id passes are still relevant and it would be great if they would also work as expected ;)

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