[rendering] Bent Normals

[Amaan Akram <xsilist(at)warpedspace.org>]

Hello everyone,

I am just trying to get my head around bent normals in Mental Ray -- 
following is my (mis?)understanding of what they are (please correct me 
if I am wrong)

-a bent normal is a direction vector that is calculated by taking an 
average of all the un-occluded samples fired from around the surface 
normal of an intersection point

-for completely un-occluded areas, a bent normal is the same as the 
surface normal

Based on the above understanding, I run two tests

Test case 1
Take a default primitive grid, plug a Vector State node straight in to 
the Surface port of the Material node and set the Vector State to 
"Normal Vector"

Test case 2
Take a default primitive grid, plug an Ambient occlusion node straight 
in to the Surface port of the Material node and set the ambient 
occlusion output mode to "Return Bent Normals (World Space)"


According to my understanding of bent normals, both the above test cases 
should produce the exact same result--but they don't. The RGB output for 
the shader in both test cases should be:
R: 0
G: 255
B: 0

The above mentioned result is the output of Test Case 1 (with Vector 
State node), but...

in Test Case 2, the RGB output is:
R: 127
G: 255
B: 127


I think the AO node is adding 0.5 to all three XYZ components before 
sending the output to a Vector2Colour node. The question is, why is 0.5 
being added?

Thanks
Amaan
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