Trouble with Fresnel and realistic lighting.

Unity Engine
1

So I was playing Star Wars: The Force Unleashed 2, and was amazed by how real the environments looked, and I want to replicate it as much as I can. My objects have always been pretty unimpressive, and even seeing plain surfaces in UDK looks more impressive than what I’ve thrown together. The objects have a dynamic to their light that I’m missing.

I recently read a bit on Fresnel and how it affects all surfaces, and I think this might be where I’m missing stuff.

As I understand it, Fresnel light shows up when the camera and light are at highly obtuse angles, making the surface appear brighter. Viewing the same surface from a more direct angle would make the surface appear more plain, with more vibrant colors.
I understand that this angle is related to the angle of reflection for water and wet surfaces.

But doesn’t this relate to specularity in some way? Does it override specularity, or is it perhaps added alongside it? And how are reflections related to both?

I suppose I’m really just so lost at this that I’m not even sure what to ask. Here’s a video with some good examples of the graphics I’m looking at, and I really want to understand what’s going on here: https://www.youtube.com/watch?v=2Hw2loyvGfg

2

It’s a multiplier for specularity.

The code for Schlick’s Approximation of Fresnel is this;

float base = 1.0 - dot( V, H );
float exponential = pow( base, 5.0 );  
float fresnel = exponential + _Fresnel * ( 1.0 - exponential );

Where;
V = viewDir
H = halfDir ( which is normalize ( view + s.Normal ) )
_Fresnel = the Fresnel reflectance value of the surface - generally very low numbers, skin is 0.028 for example, most non-metallic surfaces are less than 0.05.

So you’d multiply your specular value by the fresnel variable.

*edit: By specular value, I mean the specular highlight result from your regular specular calcuation - not the spec value from your spec texture :slight_smile:

3

Ah, thanks a bunch! I figured they’d have to be directly related, but it’s so often treated as a separate topic.

4

Bump with update. I’ve managed to make a decent Fresnel effect. Would it be appropriate to have it on a slider between a full Fresnel effect and Blinn-Phong? This is how it appears to me, and I’m trying to understand some of the math involved.

Apart from that, I do wonder how water reflection and specularity works. Is it simply a Fresnel effect as well? I’m searching for some explanations of water on the interwebs.

Addendum: The link to Unity’s default shaders seems to be broken, and the lighting shader examples don’t seem to be working right for me.

5

There’s no need for a slider. Setting your material’s _Fresnel value to 1.0 means the result is the same as your regular spec (however you’re working it out - Blinn-Phong by the sounds of it).

6

Hey dudes. could someone provide a fresnel example? i am trying to add farfarer’s fresnel code to my water shader, but i have no idea where to put it!

EDIT: ok, i am giving integration a shot. what are the H and V for?

7

I said, right beneath the code snippet…

V is the view direction.

H is the half vector, which is view direction and surface normal added together and normalised.
float3 H = normalize(viewDir + s.Normal);

8

Re-read your post, facepalm sorry about that! Them n00b moments are really getting on me… :roll_eyes:

EDIT: got a fresnel effect, but there is a black band through my water! What have i done wrong?