Chaos Corona Forum
Chaos Corona for 3ds Max => [Max] I need help! => Topic started by: Fluss on 2017-05-09, 11:16:59
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I have a few questions regarding portals :
1_ Do they strictly have to be planes or could they be custom geometry ? (example : corner windows -> corner portal or set of two planes ?)
2_ Does normals orientation matter ?
2B_ If normals orientation does not matter, admitting i have one interior shot with portals and one exterior shot. When it comes to render the exterior shot, I guess I have to hide portals as the renderer do not know that the portals are aiming to help the sampling for the interior only. Am I right ?
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I asked Ondra about the "2" few times, he told me it doesn't matter.
But honestly I still don't know about such feature...I do have scenes, where it's almost hard to identify whether interior or exterior has more content, while I want just interior to be sampled more.
I almost never have those clear cut "just air outside window, nothing else" scenes so I struggle how to place them efficiently, and unsurprisingly, it almost never does anything for me :- D
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I just made some tests with my interior.
5 passes without portals = 17,79% noise
5 passes with portals = 14,65% noise
So i guess portals help to reduce noise amount, especially in 1.6 as Ondra said :
we changed the light sampling algorithm, so more samples generated are not immediately rejected and get traced. This usually lowers noise a lot, but if the scene has heavy occlusion (windows without portals), most of those traced rays might end up being occluded. We are working on including occlusion into the mix for 1.7
👉🏼 https://forum.corona-renderer.com/index.php/topic,15931.0.html
That said, i'm kinda disappointed that portals have not any directivity, refering to the example 2B exposed above.
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Yet to test portals in 1.6, didn't know there was a change.
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2B_ If normals orientation does not matter, admitting i have one interior shot with portals and one exterior shot. When it comes to render the exterior shot, I guess I have to hide portals as the renderer do not know that the portals are aiming to help the sampling for the interior only. Am I right ?
That´s an interersting one. I recently finished a project, 2 buildings+env in the scene, shots from outside and inside(s), one with a very difficult light situation.
Both buildings had portals and surprisingly when I was inside building A (with portals active) and had also switched on the portals of building B, it gave me LOTS of noise inside building A.
Had no time to create a simple test scene to reproduce though and I´m a complete idiot in understanding how Corona portals exactly work. But it seems such a setup makes things worse.
Good Luck
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1) custom geometry is allowed, as long as you never see 2 portals in single unoccluded line from any significant point of scene (it then gives incorrect brightness)
2b) even when you render exterior with an interior visible from the exterior, portals should generally help - as the visible interior will still be the most noisy part of the scene and portals will help it.
Portals will make rendering exterior parts of an image slower, but as exteriors generally clear up much faster than interiors, it should be fine
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Ok thx for the informative feedback Ondra.