70 lines
2.2 KiB
C++
70 lines
2.2 KiB
C++
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#ifndef COOK_TORRANCE_TERM
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#define COOK_TORRANCE_TERM
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float4 cook_torrance(
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in float3 normal,
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in float3 viewer,
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in float3 light, float roughness_value, float ref_at_norm_incidence, float3 cSpecular, float3 cDiffuse)
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{
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// Compute any aliases and intermediary values
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// -------------------------------------------
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float3 half_vector = normalize( light + viewer );
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float NdotL = saturate( dot( normal, light ) );
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float NdotH = max( dot( normal, half_vector ) , 1.0e-7);
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float NdotV = saturate( dot( normal, viewer ) );
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float VdotH = saturate( dot( viewer, half_vector ) );
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float r_sq = roughness_value * roughness_value;
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// Evaluate the geometric term
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// --------------------------------
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float geo_numerator = 2.0f * NdotH;
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float geo_denominator = VdotH;
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float geo_b = (geo_numerator * NdotV ) / geo_denominator;
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float geo_c = (geo_numerator * NdotL ) / geo_denominator;
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float geo = min( 1.0f, min( geo_b, geo_c ) );
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// Now evaluate the roughness term
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// -------------------------------
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float roughness;
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float roughness_a = 1.0f / ( 4.0f * r_sq * pow( NdotH, 4 ) );
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float roughness_b = NdotH * NdotH - 1.0f;
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float roughness_c = r_sq * NdotH * NdotH;
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roughness = roughness_a * exp( roughness_b / roughness_c );
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// Next evaluate the Fresnel value
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// -------------------------------
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float fresnel = pow( 1.0f - VdotH, 5.0f );
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fresnel *= ( 1.0f - ref_at_norm_incidence );
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fresnel += ref_at_norm_incidence;
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// Put all the terms together to compute
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// the specular term in the equation
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// -------------------------------------
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float3 Rs_numerator = ( fresnel * geo * roughness );
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float Rs_denominator = max(1.0e-7, NdotV * NdotL);
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float3 Rs = Rs_numerator/ Rs_denominator;
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// Put all the parts together to generate
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// the final colour
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// --------------------------------------
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Rs = max(0, Rs);
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float3 final = max(0.0f, NdotL) *cDiffuse + (1 * Rs );
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// Return the result
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// -----------------
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return float4( final, 1.0f );
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}
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#endif
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