Volumetric lighting in H13

[TomRaynor]

Heya,

 

I have searched the forums for threads on volumetric lighting in Houdini but the majority of the posts seem to be years old.

I am doing a stadium and will need maybe a hundred or so lights producing a volumetric lighting effect, preferably with the lights using IES profiles.

 

I was wondering in this day and age of Houdini 13 what the best, cheapest and most efficient method might be for volumetric lighting?

 

Methods I am currently looking into are:

 

- The atmosphere SOP

- Volume shaders generally (such as the vex lit fog shader, which I believe is used in the atmosphere node)

- Normal lights using IES profiles shining light into true (VDB) volumes.

 

I have attached a couple of reference images to show the kind of thing I am going for.

 

Any thoughts or suggestions would be much appreciated!

 

Thanks,

Tom

[Jordan Walsh]

Have you tried the Uniform Volume shader? Apply it to a watertight mesh (a cube!) and put some lights in the middle and render with PBR.

[TomRaynor]

Are you talking about this guy (the uniform fog shader)?

 

http://www.sidefx.com/docs/houdini13.0/nodes/shop/v_uniform

 

Are you any better off using this than a standard volume or vdb in a geometry node in Houdini?

Also there seems to be relatively limited control with this node. There is a "fog colour" parameter and a "fog density" and that is all.

[Jordan Walsh]

I was talking about this one: http://www.sidefx.com/docs/houdini13.0/gallery/shop/vopmaterial/uniformvolume Get it from the shop gallery.

I havent really played with it too much so cant comment but you should only need a uniform density then do all your work with the lights.

[Serg]

We normally just make a volume box big enough to encompass the scene and let it rip with most of the lights (including the env light). The trick to render this fast is to exclude the volume itself from shadows, seems quite happy to receive shadows from other objects at very decent speeds. Because it is normally so transparent you don't miss the self shadowing at all.

 

cheers

Sergio

AXIS

[TomRaynor]

I'll give that a go Serg, thanks! I take it you are using vdb volumes?
You think this should still hold up at decent speeds with up to 100-ish lights and using light instancing?

 

Thanks again,

Tom

[Jordan Walsh]

No need to use volumes with the uniform volume shader, just add it to a watertight mesh and the shader will do the rest.

[TomRaynor]

Just testing both this morning and it as an initial observation the render seems to be much cleaner and free of noise if I use a true volume instead of using the uniform volume shader (even with volume samples set at 100)

[slamfunk]

How about the atmosphere sop in combination with the lit fog shader? I remember the lit fog shader has quite a few more parameters to tweak and was pretty fast with micropoly rendering...

[TomRaynor]

I did try that, but it seemed to get pretty damn slow when the number of lights increased.

I'm not sure how legacy/redundant that node is? Seems to have been around for a long time...

[slamfunk]

Yeah last time I used it was in H11 so I'm not sure.. But the lit fog shader seemed a step up from the uniform volume if you were gonna go down that route..

[Serg]

I meant as in a regular volume. In sops we just make a regular volume primitive and scale it up to fit the scene, the voxel res resolution can be 10x10x10 doesnt really matter. Sometimes we ramp the volume density in Y or something simple like a radial falloff. If we need to break the volume up to add texture we just do that in the volume shader.

You might want to set the active radius on your lights with the attenuation ramp to feather the edge, otherwise you might have a tiny little light on one corner of the stadium influencing the the shading at the other corner of the stadium by an infinitesimally small amount.

Hope this helps.

S

[Guest tar]

You might want to set the active radius on your lights with the attenuation ramp to feather the edge, otherwise you might have a tiny little light on one corner of the stadium influencing the the shading at the other corner of the stadium by an infinitesimally small amount.

Hope this helps.

S

 

Very, very good tip! Active Radius is super important. Without it you're sampling so much more. You can see it in the IPR buckets and when you gamma up that up.

ActiveRadius.hip