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View Full Version : bent normals to drive lights in MR?

sharktacos
01-30-2010, 04:34 PM
I was reading here:
http://www.debevec.org/HDRI2004/lan...prodreadyGI.pdf (http://www.debevec.org/HDRI2004/landis-S2002-course16-prodreadyGI.pdf)
How ILM uses bent normals to drive their lights:

"If you take a standard point or spot light, pass it the ”bent normal” rather than the original surface normal and then attenuate it with the occlusion channel, you will get a nice soft fill light source with no additional shadowing necessary"

Would it be possible to do this in Maya MR?
mister3d
01-30-2010, 04:44 PM
That's interesting. Perhaps it uses the surface normal as a radiator, but inversed (i.e. the light is coming around the object's normal).
playmesumch00ns
02-01-2010, 09:01 AM
No it's just using the average unoccluded direction as a normal for lighting calculations instead of the surface normal. A very old, very cheap hack that tends to look like, well, a very old, very cheap hack :)
sharktacos
02-01-2010, 03:50 PM
No it's just using the average unoccluded direction as a normal for lighting calculations instead of the surface normal. A very old, very cheap hack that tends to look like, well, a very old, very cheap hack :)

So how would one do this in Maya?
noizFACTORY
02-01-2010, 04:02 PM
So how would one do this in Maya?

If I remember correctly, wasn't there a bent normals mode for the mental ray occlusion surface shader?

-Sachin
sharktacos
02-01-2010, 10:49 PM
If I remember correctly, wasn't there a bent normals mode for the mental ray occlusion surface shader?

-Sachin

Yes, there is. It outputs RGB values. The question is how one would feed that into a light instead of the object normals. I tried simply putting its output into the mental ray lighting shader slot for the light. Didn't work.
sharktacos
02-07-2010, 02:33 AM
So... anyone out there know how to do this?
playmesumch00ns
02-07-2010, 10:22 AM
A quick google search turned up the following, 4th link from the top:
http://www.mymentalray.com/forum/showthread.php?t=3336

Without writing your own shader it doesn't look like you can do it for point-type lightsources out of the box.

This technique was invented before prman even did raytracing. Things have moved on a lot in the past 7 years and there are better ways of achieving the look described in the paper, like area lights.
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