Pom's Lights

[Bliz]

Pomfried, about the 'exit portal'. Could you please explain how that would be used? Is it similar to the the portal lights in Mental Ray 3.6 and above?

[Pomfried]

Since I haven't used Mental Ray I can't say anything about that.
But you would place the exit portal wherever light would usually pass through (e.g. windows) and if you are using GI you would then go ahead and make these transparent objects opaque for radiosity rays (can be done via the node editor and spot info nodes) so that GI isn't affected by your background image, but only by the exit portal. If you haven't got a background image yet, you would either add one that fits your scene, or you could go ahead and just apply a spherical map inside the light's properties.
That should be pretty much all you have to do, because the default settings most likely will be the right ones already.

[Bliz]

Thanks for the info Pomfried. I'll have to try and have a go with a test scene to fully understand it but I think I get what you're saying.

[MooseDog]

Originally Posted by Pomfried

....you would then go ahead and make these transparent objects opaque for radiosity rays (can be done via the node editor and spot info nodes) so that GI isn't affected by your background image, but only by the exit portal. ....

[3DGFXStudios]

Originally Posted by MooseDog

[Pomfried]

Originally Posted by MooseDog

Well if you don't make transparent objects opaque for radiosity rays, all surfaces will be affected by the light AND background radiosity, which for me seems kind of pointless? Not only would the illumination be a lot brighter, but would also render the exit portal kind of useless. Or am I forgetting something here ?

[MooseDog]

Originally Posted by MooseDog

sorry should have been less opaque

while i think i have a fairly firm grasp of the node system, i know it defintly falls apart when folks start talking about using it to tweak how the under-the-hood stuff for the render engine works. i'm humbled by people's understanding of that.

would it be possible to post a quick image of the node network you described? i think i understand what you're talking about concerning doubling up on illumination, but like i said, tweaking the underlying render engine with nodes like you described escapes me.

these lights are fantastic btw, thx a ton

[Pomfried]

Yeah sure, actually it's pretty easy to do:

You take the spot info node and check if the incoming ray is a radiosity ray or a preprocessing ray by just adding both output values and then pumping the result into the logic node, which then checks if the sum is 0. In that case we are not dealing with any preprocessing or radiosity, so we are safe to use our transparency gradient output, or whatever value you wish.
But if the sum actually is a non-zero value, we have to make our object 0% transparent, otherwise the background will illuminate our room in addition to the light (and might decrease lighting quality, because many radiosity samples are needed to actually find a way through holes in walls. The light however will ALWAYS be evaluated be the radiosity engine, as a consequence a lot more lighting information is available without needing to use a high sample setting for radiosity).

[MooseDog]

they say there's art in coding, and that's as clear as an example as one can find. brilliant. i'm going to give it a quick run right now.

[Pomfried]

Ok here it is. The UB version for all of you Mac users

Thanks Mike!

[Phil]

Thanks, Mike and Pomfried!

[3dworks]

Originally Posted by Pomfried

Ok here it is. The UB version for all of you Mac users

Thanks Mike!

yeah! thanks again!!!

[Iaian7]

Awesome!!

[RonGC]

Thank you both for the UB version.

Ron