LightMix bug

[marobaro]

Hi
There is a BUG in the way LightMix includes other, unintended light sources in the Environment only LightSelect element.
The problem is only activated when "occlude other lights" tick box (in CoronaLightMtl or CoronaLight) is un-checked, and
 "emit light" is ON.
No other light's, or LightMtl's parameters combinations affect the behavior. I need the "occlude other lights" unchecked on the material assigned to the fake lights above road, otherwise it is visible blocking out the Environment. So far the only way I know how to circumnavigate this problem is to switch off all other light sources and render Environment on its own. But this mean no joy in interactive LightMix. Only in photoshop. Kinda sucks.. Any ideas?
Thanks,
Marek

[TomG]

Can confirm this happens for me, but for LightMtls and CoronaLights - if Occlude is checked, then it casts a shadow in the Env LightSelect pass; if Occlude is unchecked then it casts light in the Env LightSelect pass. Not sure if that is a bug though, or just some limitation on what LightMix can do though, the developers would have to speak to that.

[maru]

If this is the same case as:

There is an object with Corona Light mtl, and this mtl uses transparency. After setting up Light Mix:
-the transparent part of the light mtl will be affected by the environment color
-only the opaque part of light mtl will be affected by its lightmix value

Then currently this is a limitation and it works like this by design. It may be fixed in the future, but currently there is no timeframe when exactly we could expect it.

[marobaro]

Well, it clearly needs re-designing now, don't it?
;)

[TomG]

I think my case may be different from that known limitation :) Sample results attached

Scene is one plane, one Corona light, some environment lighting (solid color), and basic LightMix. So no LightMtl used, and no transparency used.

- Occlude On, results are as expected. The Corona Light casts a shadow from the environment lighting, since it is occluding it. There is no illumination from the Corona Light in the Env LightSelect pass.

- Occlude Off, not sure this is expected (though could still be a current limitation) - now the Corona Light is casting some illumination in the Environment LightSelect pass (though the light is not included in that pass).

I get the same results with a CoronaLightMtl too, again without using any Transparency.

[marobaro]

Hi TomG

The same story as in my scenario. I, of course, ran tests with all types of Corona Lights and Light Materials. As soon as "occlude other lights" is un-checked the weired, unituitive behavior starts; the light (or the light material object) will impart some not needed and illogical glow to the Environment part of the LightMix element.

I trust the Corona team can see that this is hardly a desirable behavior, and fix it.

[TomG]

BTW it's not new, same results from 1.6.1 too.

It might be expected, as part of how the layers will be combined to give the beauty pass, so we will have to see if it is a bug or limitation :)

[PROH]

Hi. No these problems are definitely not new. I've reported similar (mis-)behavior a couple of times before, and no matter if it's a bug or "by design", I really hope the devs will take a look at it ASAP after 1.7.

Best Regards

[marobaro]

BTW it's not new, same results from 1.6.1 too.

It might be expected, as part of how the layers will be combined to give the beauty pass, so we will have to see if it is a bug or limitation :)

TomG
Bottom line is, with this behavior (or bug) you cannot render a "clean" LightMix element for Environment ONLY. There will always be some light contamination in Environment LightMix element coming form other light sources when the sources:
1) emit light
and
2) don't occlude other lights

..which is common scenario when I light up areas like streets, plazas, etc. Which makes it a bug in my book.