Dome Light Parameters not available

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According to the docs(19.5) there is a FallOff and FallOff Gamma parameter for shadows.

However I'm using 19.5.368 and those parameters are not available.

Is there another parameter that needs to be active in order for these two to be made available,
or has SF just got ahead of the curve and has these docs posted before the feature is actually available in a build?

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Karma Missing Parameters Dome Light.png (157.7 KB)

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I think that's a bug in the documentation. Those parameters aren't even implemented on the Light LOP (although they're present, they don't seem to do anything), and I'm not sure they'd make sense on a dome light.
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BryanRay
and I'm not sure they'd make sense on a dome light.

No? I was doing a setup with just a dome light and wanted to quickly avoid setting up other lights to get what I wanted.

With just the dome light there was a shadow cast and I wanted to increase the shadow strength (darken) a bit.

The Falloff Gamma parameter as described in the docs seems like it would do precisely what I wanted.

So in such a case, it's makes perfect sense to me.
Edited by BabaJ - 2022年10月4日 10:05:46
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that control doesn't do what you've described. It's a non-physical control for disabling shadows by distance with the falloff controlling the blend over distance.
to get the affect you describe, you would need to color correct the image in post.
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jsmack
that control doesn't do what you've described

Yet that's what the docs says it controls as I described.

jsmack
It's a non-physical control for disabling shadows by distance

Yet the docs says that's what the 'Distance' parameter is for, not the 'Falloff Gamma' as you imply here.

jsmack
to get the affect you describe, you would need to color correct the image in post.

That would not work in my case as the object being shadowed has other parts that are just as dark with same colors due to having an color image texture; Unless I make some 'Shadow Mat'. However what does work and the least amount of work other than hoping the Falloff Gamma parameter would work as described in the docs is to just use additional lights with the light linker.
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If I understand the parameters as they're supposed to work (and again, they're not actually implemented for Karma, so this is speculative), Distance controls the absolute distance from the light (I think from the light; that's what my intuition suggests) at which shadows will appear. Falloff, as jsmack says, should allow you to blend between full shadow and the clipped end of the shadow, so they fade out instead of abruptly disappearing when they hit the distance limit. Falloff gamma would control the shape of that falloff ramp. It would never be able to darken the existing shadow—only the portion of it that was being faded out by the Distance and Falloff controls. If it worked.

I still don't think it makes sense for either a Dome or Distance light because those lights aren't at any particular distance from the geometry.
Edited by BryanRay - 2022年10月4日 12:16:29
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Ok...even in my response to jsmack, I'm seeing what's happening is that I'm on a different page as to what both falloff and distance as used in the docs is referring too( It can be interpretted in more than one way, but since you guys have more experience and have seen 'falloff' used in other contexts; Your way is the 'correct' way to look at it. So no use in me making some diagram to explain how I interpreted what falloff and distance was referring too, so that I would think the falloff gamma would do as I thought.)
Aside from the fact it's not available but only in docs makes the discussion moot.

BryanRay
I still don't think it makes sense for either a Dome or Distance light because those lights aren't at any particular distance from the geometry.
No, but there is a distance from the object casting the shadow to the object receiving the shadow, so in terms of 'making sense'; Yes it makes perfect sense if it was implemented, as yes I did have a use for it.

Now whether or not I wish it would be a feature is another topic and I really don't care to for it to be implemented so I am not going to send in an RFE. I simply saw it in the docs and was wondering why it's not on the node itself; Thought perhaps I just need to 'turn' something else on to make it available, which was the point of the post. That's all.

Seems like you say it is a doc 'bug' and doesn't really belong there.
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For what it's worth, the USD docs don't really shed any light (pun very much intended) on what the distance is supposed to be, either. Our lead Karma dev agrees with you: he thinks it's supposed to be the distance between the shadow caster and the shadow receiver geo. But we'll probably have to investigate whatever Renderman is doing with it to find out what Pixar intended.
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BabaJ
No, but there is a distance from the object casting the shadow to the object receiving the shadow, so in terms of 'making sense'; Yes it makes perfect sense if it was implemented, as yes I did have a use for it.

Shadows are not cast, lights are either occluded or not. The distance between one blocker and another doesn't enter into any of the lighting calculations. These shadow distance controls only consider the distance between the light source and the surface being illuminated.

BryanRay
If I understand the parameters as they're supposed to work (and again, they're not actually implemented for Karma, so this is speculative), Distance controls the absolute distance from the light (I think from the light; that's what my intuition suggests) at which shadows will appear. Falloff, as jsmack says, should allow you to blend between full shadow and the clipped end of the shadow, so they fade out instead of abruptly disappearing when they hit the distance limit. Falloff gamma would control the shape of that falloff ramp. It would never be able to darken the existing shadow—only the portion of it that was being faded out by the Distance and Falloff controls. If it worked.

This is how I understood it from the description given. It's something like
Of = select(isshadowray(), pow(fit(distance(L, P), falloff, distance, 1, 0), falloffgamma), Of)
Edited by jsmack - 2022年10月5日 14:25:15
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jsmack
Shadows are not cast, lights are either occluded or not. The distance between one blocker and another doesn't enter into any of the lighting calculations. These shadow distance controls only consider the distance between the light source and the surface being illuminated.

My response to BryonRay was not meant to say anything that would contradict what you just said here.
My point was that it is a 'piece' of information that could be used in relation/addition too, how the actual shadow gets rendered.
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