Author Topic: Bidir - problem with visibility caustics  (Read 11838 times)

2013-05-31, 11:42:46

Polymax

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1. Why caustic exists, but in the water it is not visible in the bidir mode?
2. Why is the shadow of the water shifted relative to the caustic?
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2013-05-31, 12:07:11
Reply #1

Ondra

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1&2: physics.
caustics are shifted because the light from sun is refracted. This means it changes direction and hits the surface in different place that it would on its own, forming the caustics and shadows, such as here:


The reason your results look unnatural is because your setup is unnatural - your media are not correct, some of the rays hit the floor while in air and other hit the same place while in water. To correct this you would either have to model the water twosided, or make the pool water enclosed, like in reality. Then you would no longer get such effect.

The caustics visible through water are not missing, it just has MUCH higher variance, because it represents an SDS (specular-diffuse-specular) light path, which is extremely difficult for BDPT to render. You have few fireflies there, these fireflies are so bright, that they "contain the entire caustics intensity from surrounding areas" (simplified), so it is unbiased in the end (no energy is missing). To render it efficiently you would need different light connection strategy, like progressive photon mapping, or VCM (which is BDPT + progressive photon mapping combined). Try it and you will se the missing caustics.
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2013-05-31, 12:27:03
Reply #2

Polymax

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1. I am ashamed! I missed it ((
2. Here everything is clear!
Thanx for answer!
Corona - the best rendering solution!

2013-05-31, 18:14:08
Reply #3

jjaz82

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this is a common problem in many Unbiased render, also maxwell etc.
if I remember correctly thearender had solved the problem of time to get caustic  through dielectric material, but i don't know how..

2013-05-31, 18:22:56
Reply #4

Ondra

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this is a common problem in many Unbiased render, also maxwell etc.
if I remember correctly thearender had solved the problem of time to get caustic  through dielectric material, but i don't know how..
This is also problem in biased renders, they just dont bother to even try to render this.

BTW: the problem is now solved in 90% instances with Vertex Connection and Merging (http://www.smallvcm.com/), which Corona implements ;)
Rendering is magic.
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2013-05-31, 18:36:51
Reply #5

jjaz82

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ondra, not a day goes by that you do not make us a nice surprise :D

2013-05-31, 18:49:52
Reply #6

Ondra

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this is implemented since last fall ;)
Rendering is magic.
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2013-05-31, 19:10:52
Reply #7

jjaz82

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ok surprise for me :D hi hi

2013-06-14, 21:26:59
Reply #8

jjaz82

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Polymax have you tried bidir with glass in hybrid mode? i know it's a fake but maybe in some cases can work..
this is my test...


2013-06-14, 23:23:38
Reply #9

Ondra

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Polymax have you tried bidir with glass in hybrid mode? i know it's a fake but maybe in some cases can work..
this is my test...
This is resul with which algorithm?
Rendering is magic.
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2013-06-15, 01:09:41
Reply #10

jjaz82

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2013-06-15, 01:39:53
Reply #11

Ondra

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so bidir - primary+secondary solver choices get ignored when using bidir. Just switch to VCM and you will get nice caustics without fakes (with solid glass)
Rendering is magic.
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2013-06-15, 07:39:19
Reply #12

jjaz82

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ohh... perfect... :D

2013-06-15, 11:05:13
Reply #13

iliyang

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To reduce the noise in the caustics, make the ground plane as small as possible. The larger it is, the more photons traced from the sun are wasted.

2013-06-15, 11:52:21
Reply #14

Ondra

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To reduce the noise in the caustics, make the ground plane as small as possible. The larger it is, the more photons traced from the sun are wasted.
Unfortunately when using sun you cannot break it that easily ;)
Rendering is magic.
Private scene uploader | How to get minidumps for crashed/frozen 3ds Max | Sorry for short replies, brief responses = more time to develop Corona ;)