Light scattering

[michael_g]

How do I make god rays in Octane? I understand how to do it using a volume in Luxrender but so far it`s escaping me in Octane, is some thing to do with the scatter node?

[t_3]

How do I make god rays in Octane? I understand how to do it using a volume in Luxrender but so far it`s escaping me in Octane, is some thing to do with the scatter node?

yes: https://www.youtube.com/watch?v=MqOZp77ZSLg
in addition i found that very helpful: http://render.otoy.com/forum/viewtopic. ... 77#p173977
and a basic explanation of how medium nodes work: http://render.otoy.com/forum/viewtopic.php?f=21&t=9380

the point is to create a volume that contains the whole scene, and to set it up with specular material with a scattering medium node. since the camera needs to be _outside_ of the medium you can either create a volume geometry like shown in the video (of course not really possible with studio alone), or use the trick ROUBAL posted;

the probably hardest part is to get the various values right, might need quite some trial and error...

[michael_g]

Thanks T_3

[t_3]

Thanks T_3

a ps: if you want to use mesh lights, you need to put them inside the fog volume; the "glow" is going to be the better visible the smaller the light source is; and of course a directional light (i.e. light coming out of a tube sort of poor mans spot light) is going to work much better than an omnidirectional light; would be interesting if ies lights produce visible light cones - haven't tested it myself...

[linvanchene]

edited and removed by user

[t_3]

cool thing that it works with ies also; is probably a lot easier to create lamps with a explicit light cone.

about the bubble: negative scale does indeed invert normals, but it maybe doesn't work when octane is creating new normals; here is a sphere with positive scale and inward normals:

FogBubble.rar

(16.75 KiB) Downloaded 184 times

the size of the sphere can imo range from clipping distance to whatever fits - it just defines in which distance to the camera the fog volume begins; will imo affect the visible dense, and should of course cover all light sources or the areas where godrays should be visible.

btw you only need to parent the sphere object to the active camera (and reset all translations of the sphere of course) to have it exactly where needed and make it move with the camera...

[michael_g]

Greta info thanks.

[DrHemulen]

Awesome What's the perfomance hit for this kind of stuff?

[michael_g]

Awesome What's the performance hit for this kind of stuff?

I guess it depends on your hardware but during tests I did this morning I had to lower the eye depth and keep the res at 720x480. It`s a lot harder for the render kernel to project the light rays through a volume.

My hardware is a 770gtx and a 650ti.

[t_3]

Awesome What's the perfomance hit for this kind of stuff?

hard to tell. normally there won't be much drop in ms/sec speed, but it will need quite some time more to get the image to the desired (low) noise level; 50% longer, twice as long - depends on the scene...