Volumetric light/halo/godray/dust etc.

[Juschu]

Hi everybody,

I'm kind of desperate, because I've been searching for this topic about two weeks now and I've checked almost every result google has found...(including the threads in this forum... Unfortunately the luxrender wiki hasn't helped me out either) However, I've found out, that I have to use a cube with material "boundvolume", which surrounds the scene (the light source), that absportion and scattering should be a dark grey (however, other colours- if they are dark or bright- dont work either) and emission black. I've also learnt that the bidirectional integrator doesn't support this, and that I should use the path integrator. I 've tried several things out but it never worked out. No dust/fog/halo effect as I was wishing. I also imported the boundvolume from a blender scene in another forum, which was provided for this question, and in my scene it didn't work, although it seemed, that it had the same setups as before in the scene where it had worked perfectly.

I've only started with blender and luxrender lately, so I don't really have much understanding of the technical implications (I'm sorry for that!), so maybe there are just another settings to do before or to check.

Could my scene be too light, or the sunrays too weak? The light is coming from several (15) small roof windows, not from a "normal size" windows in a wall. I have really no idea how to get it done.

Can anybody provide some advice?

[Juschu]

BTW, my Version is release candidate 6.6, I'm using windows (sorry for that).

[tomb]

Depending on the dimensions of your scene/bounding box you probably need to tweak/lower the step size (and scattering/absorbtion parameters) in luxblend - just fool around with the params, you'll figure it out The whole volume system is pretty rudimentary per now and will be rewritten after 0.6 is out

[psychotron]

I'm using windows (sorry for that).

nice

[Dade]

I attached to this post a blender scene that is a simple example of volume rendering:

First of all, I suggest you to build a simple scene (as the one attached to this post) where you can do tests and learn how the volume rendering parameters work.

Once you have built your scene (don't forget to use portals), you can start to work on the volume rendering part. You have to add a cube surrounding all the scene, this will define the volume where the volume rendering will happen:

Assign a material to this cube (i.e. "mat_volume") and define the material in Luxblend as follow:

Absorption: this parameter defines how "foggy" the scene is. Increase the values if you want to reduce how far you can see and vice versa;

Scattering: this parameter define how much the light is scattered around. If you want a more dramatic "blade of light" effect, increase the values (or vice versa);

Enable volume rendering by selecting "simple" integrator in the Render tab:

Stepsize: This value will have a huge impact on the rendering time. It defines the length of the ray marching steps. It can be used to tune how precise will be the result of the volume rendering (i.e. + or - noise). Cut in half the value and the result will be about 2 times more accurate but it will double the rendering times too. If you are going to use a lot of samples per pixel (i.e 1000 or more) in the final rendering, I suggest to use large steps in order to speedup the rendering (i.e 1.0 or more).

And you are ready for the rendering:

P.S. if you use volume rendering, be ready for looooong rendering time

[Atom]

Thanks for the test scene!

[Juschu]

Thanks a lot for the interesting explication of the parameters!

I've tested some simpler scenes before with different parameters, it has never worked so far...I also used portals...but i'll go on trying. Could it be that the fog emerges not until some significant render time?
But in the premade scene I got from the other forum first you could see immediately the light rays.

[jeanphi]

Hi,

Currently volume rendering doesn't work with all integrators, it most noticeably doesn't work at all with bidirectional.
It should work with direct lighting and path.

Jeanphi

[david]

Hello:

I've been playing with the volumetric lights. This feature offers a fantastic results.
But I don't know how works the emission channel, or what is the meaning of it.

Thank you

[jeanphi]

Hi,

This to to make a volumetric light: the volume itself emits light.

Jeanphi