Shader - Fresnel Warp

Ace-Angel

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++

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

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++

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++

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

Cheers Drew, much appreciated

kodde

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

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

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

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.....