Shader - Fresnel Warp

Ace-Angel · Nov 2012

Heya people, how you doing?

I was taking a gander on some materials from the Source engine, and came across this line:

$FRESNELWARP "fresnelranges"

From what I understood, it's basically a textures that wraps around the model, but with a Fresnel as it's feed? Although I'm not too sure about it.

I also tried looking for the written shaders, but cannot find them, so if anyone has any idea what I need to do, that would be grand.

Drew++ · Nov 2012

hmm, it might be something like this.

float3 vReflect = reflect( -vEyeDir, vWorldNormal );                // Reflect view through normal
float LdotR = saturate(dot( vReflect, vLightDir ));                    // L.R    (use half-angle instead?)
specularLighting = pow( LdotR, fSpecularExponent );                    // Raise to specular exponent

// Optionally warp as function of scalar specular and fresnel
if ( bDoSpecularWarp )
specularLighting *= tex2D( specularWarpSampler, float2(specularLighting.x, fFresnel) ); // Sample at { (L.R)^k, fresnel }

specularLighting *= saturate(dot( vWorldNormal, vLightDir ));        // Mask with N.L
specularLighting *= color;                                            // Modulate with light color

I'm not 100% sure though. Test it out!

Ace-Angel · Nov 2012

Hey Drew, cheers for the snippet, it looks good on my end (just had to change a few things around to compensate for Max :P ) Looking back on the documents and Source shader, it seems like there is some extra magic going on?

Here is what I mean:

Just to be clear, you code worked perfectly fine with the Fresnel Warping lookup texture, so much kudos for that.

In the document, it's also talking about a warp color texture, which is supposed to be related to the Fresnel Warp, but I have no idea what it is and my google-fu in said terms is coming up empty.

If you (or anyone else) have hints on what it could be, that would be very much appreciated, because I'm honestly lost on what a 3D Texture which looks like a UV Map is supposed to be or if I'm reading too much into it and it's infact a simple XYZ projection.

Cheers!

Drew++ · Nov 2012

Yeah it's basically the same thing, but for diffuse light & using a tex1D

// fResult is a saturated dot(N, L); 
// Don't forget half lambert, if needed! saturate(NDotL * 0.5 + 0.5);   
 
if ( bDoLightingWarp )
{
   fResult = 2.0f * tex1D( lightWarpSampler, fResult );
}

*edit* a buddy if mine has a cool implementation of this, has a neat trick for smoothing it out. http://blog.legend286.co.uk/lightwarps/

Drew++ · Nov 2012

Oh, another thing if you're doing it half-lambert, it needs to be squared.

here's how the code should be all-together

float3 DiffuseTerm( float3 worldNormal, float3 lightDir)
{
    float fResult;

    float NDotL = dot( worldNormal, lightDir );    // Unsaturated dot (-1 to 1 range)

    if ( bHalfLambert )
    {
        fResult = saturate(NDotL * 0.5 + 0.5); // Scale and bias to 0 to 1 range

        if ( !bDoLightingWarp )
        {
            fResult *= fResult;    // Square
        }
    }
    else
    {
        fResult = saturate( NDotL ); // Saturate pure Lambertian term
    }

    float3 fOut = float3( fResult, fResult, fResult );
    
    if ( bDoLightingWarp )
    {
        fOut = 2.0f * tex1D( lightWarpSampler, fResult );
    }

    return fOut;
}

Ace-Angel · Nov 2012

Cheers Drew, much appreciated

kodde · Nov 2012

Sorry if I missed this, but what do the 3 axises in the 3D-texture represent? The direction of the surface normal in camera space?

Ashaman73 · Nov 2012

In the document, it's also talking about a warp color texture, which is supposed to be related to the Fresnel Warp

From this doc I would say, that it is very similar to a color correction LUT (lookup table). That is you map the present RGB color to new RGB color (therefore a 3d texture). Instead of applying it to the whole scene (=>color correction post processing) you can apply it to the source texture. Either completely (fresnel mask=0) or at the silhouette of the model (fresnel term & mask).

The effect is most likely an artistic accentuation of the silhouette. The mask seems to support both effects, the light warp and the color fresnel term.

Ashaman73 · Nov 2012

Pseudo shader code(color fresnel warp):
vec3 textureColor = tex2d(modelTexture, uv);
float fresnelMask = tex2d(fresnelTexture,uv);
vec3 warpedColor = tex3d(warpTexture, textureColor.rgb);
float fresnelTerm = calculateFresnelTerm(viewVector,normalVector);
float alpha = fresnelTerm * fresnelMask ;
vec3 finalColor = alpha * warpedColor + (1-alpha) * textureColor;

Hazardous · Nov 2012

kodde wrote: »

Sorry if I missed this, but what do the 3 axises in the 3D-texture represent? The direction of the surface normal in camera space?

Exact same question I had.

Is it basically to drive the color of the fresnel?

EDIT: Duh... just read valve's pic. lol

proceed.....

Shader - Fresnel Warp

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