Arnold Caustics and Refracted Shadows

[Tony Cosgrove]

Hi All,

So I've recently been trying out Arnold to extend my rendering knowledge.

And I'm here doing a simple test of recreating a glass object; something that is simple in Vray and even possible in Mental Ray. Yet it seems fairly ambiguous in Arnold to get it going.

Basically I'm looking to have my object cast caustics onto a ground plane, with some realistic shadows (ie a wine glass, jug).

I am getting transparent shadows, yet I find them to be very flat (rather than darker in areas of thicker glass and light in others) and then when I switch "caustics" on, its just an overpowering glow that leaves the shadows with hardly any shading.

I have asked our good friend google and found very little, so I was wondering if any Arnold users out there have a recommended workflow that gets that 'sharp' caustic look. I appreciate Solid Angle have stated on their site that they haven't yet catered for 'hard caustic emanating from bright direct light sources'. But I was wondering if there was a way to fake it.

Cheers,

Tony

[matt estela]

From what I understand Arnold is a unidirectional pathtracer, caustics is one of those worst case scenarios for that; you need to trace photons from the light into the scene, whereas arnold and similar renderers only really trace backwards from the camera into the scene. To get a cohesive set of ray hits to trace out pretty caustic pattern would requite far too many rays to be practical. Mentalray and vray both allow for photon mapping, hence both can achieve this effect at lower cost.

That said, in production I've found I've rarely needed this feature. Unless I was doing jewellery visualisations or the cover of the next pbrt book, I've found it faster to find nice caustic images via google, and map it into a light. All the refractive caustic shiny effects in The Lego Movie were done this way, usually very specifically art directed.

Of course, this is where you say that you're doing a sweet diamond ring images for the next cover of the pbrt book. :)

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[Tony Cosgrove]

Thanks Matt,

Yeah that was going to be my last resort, I did want just to try and get true caustics. But alas it looks like its not going to happen.

No front cover of the pbrt just yet :)

Cheers,