Bi-Dir & Mirror

[zeealpal]

Just something I noticed, Im not sure if this has been brought up before, but I noticed that the caustics from the Sun > Refract in Water > Reflect in Mirror > Land on floor... they dont reflect back into the mirror. Is there a particular fix for this, a known issue or should I try SPPM?

[Dade]

Just something I noticed, Im not sure if this has been brought up before, but I noticed that the caustics from the Sun > Refract in Water > Reflect in Mirror > Land on floor... they dont reflect back into the mirror. Is there a particular fix for this, a known issue or should I try SPPM?

BiDir is unable to render SDS (i.e. light specular -> diffuse -> specular bounces). It is exactly the kind of light interaction where SPPM is superior to BiDir.

[Vutshi]

You may try to add some roughness to the mirror. It helps when there is an SDS path involving glass (viewtopic.php?f=14&t=7049). It should work with mirrors.

[Meelis]

Is this possible to impliment SDS for bidir?

[SATtva]

No, it is a shortcoming of path tracing algorithms.

[Lord Crc]

Is this possible to impliment SDS for bidir?

I read a paper which combined Bidir and SPPM techniques in a sense, allowing to merge vertexes if they were close by, similar to how photons in SPPM contribute to nearby hitpoints. Should allow for bidir to handle these cases. However, how hard it is to implement into luxrender is not for me to say

[jeanphi]

Hi,

First note that bidir does implement the rendering of SDS paths, they are just very long to converge. The only case when they are impossible to render is when you use a point light.
It should be possible to implement vertex merging in LuxRender but the main issue is the probabilities computations for a path, they could become very difficult to handle.

Jeanphi

[zeealpal]

The lamp was sun type for this scene, just to let you know

[Vutshi]

I would like to participate in a mega project for rendering this scene with BiDir until it will converge and the reflection appears in the mirror. Just curious how many samples per pixel are really needed for such scenes.

[Dade]

I would like to participate in a mega project for rendering this scene with BiDir until it will converge and the reflection appears in the mirror. Just curious how many samples per pixel are really needed for such scenes.

Given the size of the light source (i.e. sun disk), it will probably never converge because of the resolution of floating point numbers.