better fresnel for dual lobe

[Alessandro Padovani]

This is related to #555. This is also related to #25 as it is meant to improve the fresnel effect. The fresnel effect is what we perceive as reflection and depends both on the surface roughness and light incidence. Now in my tests it seems the light incidence is treated differently in the uber shader and the pbrskin shader. So we get two fresnel effects.

Please understand that this is a complex matter and these results are intended to be an improvement but they are not a 100% match with iray anyway.

[Alessandro Padovani]

Below it's the setup for the daz fresnel for the uber shader. I just added a power by 2 for the roughness that seems to match better.

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Then a couple tests, first iray, then cycles, then the fix.

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[Alessandro Padovani]

Below it's the setup for the daz fresnel for the pbrskin shader. This time I added a power by 4 for the roughness that seems to match better.

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Then again a couple tests, first iray, then cycles, then the fix.

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[Thomas Larsson]

Implemented in last commit. Actually I only tested the uber case, since I didn’t have any pbrskin asset readily available, but since they only differ by the exponent I hope that should work too.

[Alessandro Padovani]

Commit 1e9a95c doesn’t work as intended. It is my fault since I was not clear enough. The new fresnel is intended for the daz dual lobe group, it is visible in the pictures above but I didn’t mention it. So the simple blender fresnel in the uber dual lobe needs to be replaced.

I’d not change the general fresnel outside dual lobe for now. That is, below it’s G8F that doesn’t use dual lobe and the general daz fresnel group without the power node seems to work fine enough in this case.

Or we may use a more flexible daz fresnel group with a power input that can be 1 or 2 or 4 depending on the case.

# daz fresnel power
general fresnel: power = 1
uber dual lobe: power = 2
pbrskin dual lobe: power = 4

Also changing the title accordingly.

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[Thomas Larsson]

Fixed in last commit.

[Alessandro Padovani]

Commit cdda469 is not good.

The uber dual lobe doesn’t connect the roughness channels. This way the power node is useless if the roughness is not connected.

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The pbrskin dual lobe works fine.

The daz fresnel with no dual lobe works fine.

[Thomas Larsson]

Looks like a line disappeared from the code for some reason. Fixed now.

[Alessandro Padovani]

Commit 24b8685 works great thank you Thomas for the fast fix.