UDK - Diffuse-Power Slot - What does it exactly do?

Ace-Angel

Hey to all,

I was wondering if anyone knew what exactly Diffuse power was used for in UDK's material.

From what I was able to read up on, it essentially Specular-Power/Glossiness, but for the diffuse only...which really doesn't make sense for me in my head.

I tried playing around with it, but the effects were really weird, and I couldn't exactly understand what I was looking for in terms of visual difference.

Anyone mind giving me a quick idea?

glynnsmith

I thought it was how much your lightmass bake takes coloured bounce lighting from the diffuse.

I could be totally wrong, though. It's been a while.

Ace-Angel

Hey, don't ask me, I'm the one who's asking ;p

Jokes aside, from what I was able to see, it gives my some kind of glossiness effect, it turned for example, a deep blue material, which had an Orange Spec map, almost orange like even in the diffuse.

Gave it a nice 'rough' orange look. I'm thinking maybe it can be adjusted as 'roughness' if ones heart desires and use a large scale noise map? Although, from light hit angles, it looks more like glossiness, but again, it doesn't make sense on why you would want to TWO Gloss like slots to be used, since it would only become heavier.

I also took into consideration the bakes, as you said. Gave it a whirl. Simple dominant light, and didn't really see a surface change on my model. Could it be obsolete?

glynnsmith

Ack. Diffuse boost is the value that affects Lightmass bounce lighting.

Diffuse Boost - A multiplier for the amount of influence the diffuse component of the material has on static lighting.

Just had a quick look through the UDN, and it looks like EPIC have yet to write up what Diffuse Power means :P

Diffuse Power
TODO

With that clarified, I can't say I've ever used it, or seen it being used specifically.

Ace-Angel

Ah, bollocks...silly Epic.

Vailias

If the diffuse is calculated as a phong or lambertisn term (like it probably is) then diffuse power should have the same effect on model lighting as spec power does on specular lighting. Ie make it More directional and less diffused.

Just slap a constant medium grey into the diffuse slot, then put a scalar into the diff power slot and see what the effect is.

Sandro

Ahh, haven't noticed this slot before. Seems like roughness parameter to me. Super snazzy for certain types of concrete and clothing. Would be cool to attempt awesome shading style Leyendecker had, with super sharp cores and abrupt light to dark transitions.

equil

right, it's just a (seemingly normalized) power function. maybe something like pow(NdotL, diffusepower) * diffusepower, and then that's multiplied together with the diffuse texture.

in layman's terms you'd probably call it diffuse falloff instead. any values above 1 makes the diffuse term softer, and any value below 1 makes it harder.

Ace-Angel

Yeah, UDK uses a Phong based material by default, also, I see what you guys mean now.

It looks extremely weird, and I'm confused as to how one would get the most benefit out of it, although something struck me as abit off in the video I used as an example.

[ame="http://www.youtube.com/watch?v=-x5fgnoQfbU"]UDK - Diffuse Power - Test - YouTube[/ame]

I just realized on how similar it is to something else I was studying a few week ago:
http://filmicgames.com/archives/557

I was trying to implement a fresnel, based upon directional based specular like material, which could be, through certain vectors, be displayed to give the mesh it's own 'shade' but a la specular style without being dependent on gloss or specular limitations.

So I'm thinking of putting it under 'Roughness', since I just tried (not displayed in video) a quick Carbon based material, and alongside the Specular, it seems more of a pop for my Diffuse which out be otherwise a nightmare to try and achieve through floating normal maps.

If anyone of you guys (and anyone else) has more feedback in that regard, please do share, it would be much appreciated.