Glossiness/Roughness for Schlick - How to do it?

Ace-Angel · Oct 2012

Hey to all,

I was wondering if there is any way you could move the Specular Highlight additively from the light Vector for a Schlick?

An example of what I mean:

The white is the object, the Grey is the traditional spec from the Light Vector position. I would like to achieve something like Yellow, in which I essentially 'compress' or tighten the term.

Any tips? Cheers!

Drew++ · Oct 2012

What kind of specular model are you using this Schlick fresnel with?

"standard", it's

float base = 1.0 - dot(V, H);
float exponent = pow(base, 5.0);              
float fresnel = exponent + F0 * ( 1 - exponent );

You might try to divide that last bit by a value, to get a 'roll off'

Here's a Kelemen Szirmay-Kalos brdf/specular w/ schlick

float Specular( float3 V, float3 N, float3 L, float4 eccentricity, float rollOff, float4 weight )
{
   float spec = 0;
   
   float cosne = dot( V, N );
   float cosln = dot( N, L );
   
   if( cosln > 0 )
   {
      float3 h = L + V;
      float3 H = normalize( h );
   
      float coseh = dot( H, V );
      float cosnh = dot( H, N );
      
      float cosnhPow2 = cosnh * cosnh;
      float ta = sqrt( 1 - cosnhPow2 ) / cosnh;

   
      float cosnhPow4 = cosnhPow2*cosnhPow2;
      float4 eccPow2 = eccentricity * eccentricity;
      
      float4 pH = exp( -( ta * ta )  / ( eccPow2 ) ) / ( eccPow2 * cosnhPow4 );
      
      // This Schlick Fresnel is a bit different than a standard Schlick imo...
      float cosehPow = pow( 1 - coseh, 5.0 );
               
      float Ff = cosehPow + ( 1 - cosehPow ) / rollOff; // Rolloff might be what you need ;)
      
      float4 specCoeff = max ( ( pH * Ff ) / dot( h, h ), 0 );
      
      spec = saturate( cosln ) * dot( specCoeff, weight );
               
   }
   
   
   return spec;
}

Ace-Angel · Oct 2012

Cheers Drew, you're awesome as always

Will Faucher · Oct 2012

Sorry. I had to.

equil · Oct 2012

and no one laughed.

- - - -

i wonder if you want behaviour like this?

i think that's just using a szirmay-kalos geometry/masking term ( dot(L+V,L+V) ).

Ace-Angel · Oct 2012

Actually Equil, that would be very useful indeed, however, the only way I was able to get that effect (the one in the second row column) is my Multiplying a Phong Specular by a Schlick and clamping it by a Lambert, with a really high constant value to bring back the 'brightness'.

I tried sampling the May-Kalo shader and it's terms, but none of them seem to behave the way that way.

Glossiness/Roughness for Schlick - How to do it?

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