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Rendering with Arnold in Houdini and Solaris using the HtoA plug-in.
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Lightsource seen through glass in reflection

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Message 1 of 6
mail
195 Views, 5 Replies

Lightsource seen through glass in reflection

I have an error that I could reproduce in a fresh scene with the following setup:

 

A vertical plane with a mirror shader (all 0 except for spec 1) - a little offset (in normal direction) parallel another plane with a rough glass shader (all 0 except for transmission, and rough set to 1). Further in that direction there is a light source. Sandwiched in between the first and second plane is the camera, looking towards the mirror.

 

Imagine the camera looking into the bathroom mirror, seeing the frosted glass shower (behind the camera). Inside the frosted glass shower is a light source.

 

However no matter how rough I set the (frosted) glass shader the reflection of the glass and lightsource (through the glass) is always crisp sharp. It feels like there is some optimization going on that I can't turn off.

 

In ray speak: The camera ray gets reflected on the mirror surface, travels through the (rough) glass surface and eventually lands on the lightsource. However the (rough) glass surface always acts like a perfect smooth surface - I can't get it to diffuse the light source behind it.

 

Any suggestions? (I'm behind a no-machine network so I can't share even a simple scene).

5 REPLIES 5
Message 2 of 6
lee_griggs
in reply to: mail

Can you share an image?

Lee Griggs
Arnold rendering specialist
AUTODESK
Message 3 of 6
mail
in reply to: mail

I attached a screenshot.
M is the mirror (single wall) - I put two checkerboards on it so in the render it is visible. In the black stripes it shows the 100% spec shader (in the grey areas the checkerboards - ignore those)
G is the glass pane (single wall) - you can see the shader on the right side

L is a disc light. I started with a meshlight, but the effect also shows beautifully with an arnold light

C is the camera looking towards the mirror (-> ray is reflected off the mirror, through the glass onto the lightsource)



On the bottom there's the render (again, ignore the grey checkerboard areas). The reflection of the lightsource is crispy sharp with a slight halo. If I turn Specular to 0 on the light source I get what I would expect: a blurry bright orb. However I don't want to turn Specular to 0 in my scene. And either way the crispy reflection seems odd from a physical/real world standpoint.

 

mail_0-1680083123960.png

 

Message 4 of 6
thiago.ize
in reply to: mail

My quick guess is that what you want to see is a caustic (light bending through glass) and Arnold by default disables that since usually that results in large amounts of noise. What happens if you enable caustics in your standard surface shaders?

Message 5 of 6
Stephen.Blair
in reply to: thiago.ize


@thiago.ize wrote:

My quick guess is that what you want to see is a caustic (light bending through glass) and Arnold by default disables that since usually that results in large amounts of noise. What happens if you enable caustics in your standard surface shaders?


I didn't see any diff when I tried that. This came up back in 2017 too and I don't think we handle this situation...if memory serves...no way to enable it



// Stephen Blair
// Arnold Renderer Support
Message 6 of 6
thiago.ize
in reply to: mail

Right Stephen, you might also need to force the glass to not be transparent to shadow rays since you now want caustics to take over that task. You can do that by using a ray switch for the glass shader connected to everything except shadow rays

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