demotool/shaders/lib/shading-pbr.glsl

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2017-10-04 19:06:50 +02:00
//! type library
//! include lib/utils.glsl
struct T_PBRMaterial
{
vec3 cAlbedo;
float roughness;
float metallic;
float subsurface;
float anisotropy;
float specular; // Specular strengh for non-metals
float specularTint; // Albedo color% in specular tint (non-metals)
};
// -----------------------------------------------------------------------------
float PBR_SchlickFresnel(
in float u )
{
const float m = clamp( 1 - u , 0 , 1 ) ,
m2 = m * m;
return m2 * m2 * m;
}
float PBR_GTR2Aniso(
in float nDotH ,
in float hDotX ,
in float hDotY ,
in float ax ,
in float ay )
{
float x = hDotX / ax , y = hDotY / ay ,
p = x * x + y * y + nDotH * nDotH;
return 1 / ( PI * ax * ay * p * p );
}
float PBR_SmithGGXAniso(
in float nDotV ,
in float vDotX ,
in float vDotY ,
in float ax ,
in float ay )
{
float x = vDotX * ax , y = vDotY * ay;
return 1 / ( nDotV + sqrt( x * x + y * y + nDotV * nDotV ) );
}
vec3 PBR_Shade(
in T_PBRMaterial material ,
in vec3 camDir ,
in vec3 normal ,
in vec3 lightDir )
{
float nDotL = dot( normal , lightDir ) ,
nDotV = dot( normal , camDir );
if ( nDotL < 0 || nDotV < 0 ) {
return vec3( 0 );
}
vec3 tangent = cross( vec3( 0 , 1 , 0 ) , normal );
if ( length( tangent ) == 0 ) {
tangent = cross( vec3( 1 , 0 , 0 ) , normal );
}
tangent = normalize( tangent );
vec3 bitangent = normalize( cross( normal , tangent ) );
vec3 halfVec = normalize( lightDir + camDir ) ,
tint = M_NormalizeColor( material.cAlbedo ) ,
cSpecular = mix( material.specular * .08 * mix(
vec3( 1 ) , tint , material.specularTint ) ,
material.cAlbedo , material.metallic );
//vec3 Csheen = mix(vec3(1), Ctint, sheenTint);
float nDotH = dot( normal , halfVec ) ,
lDotH = dot( lightDir , halfVec ) ,
// Diffuse fresnel - go from 1 at normal incidence to .5 at grazing
// and mix in diffuse retro-reflection based on roughness
FL = PBR_SchlickFresnel( nDotL ) ,
FV = PBR_SchlickFresnel( nDotV ) ,
Fd90 = 0.5 + 2 * lDotH * lDotH * material.roughness ,
Fd = mix( 1 , Fd90 , FL ) * mix( 1 , Fd90 , FV ) ,
// Based on Hanrahan-Krueger brdf approximation of isotropic bssrdf
// 1.25 scale is used to (roughly) preserve albedo
// Fss90 used to "flatten" retroreflection based on roughness
Fss90 = lDotH * lDotH * material.roughness ,
Fss = mix( 1 , Fss90 , FL ) * mix( 1 , Fss90 , FV ) ,
ss = 1.25 * ( Fss * ( 1 / ( nDotL + nDotV ) - .5 ) + .5 ) ,
// Specular
aspect = sqrt( 1 - material.anisotropy * .9 ) ,
rsqr = material.roughness * material.roughness ,
ax = max( .001, rsqr / aspect ) ,
ay = max( .001, rsqr * aspect ) ,
Ds = PBR_GTR2Aniso( nDotH , dot( halfVec , tangent ) ,
dot( halfVec , bitangent ) , ax , ay ) ,
FH = PBR_SchlickFresnel( lDotH ) ,
Gs = PBR_SmithGGXAniso( nDotL , dot( lightDir , tangent ) ,
dot( lightDir , bitangent ) , ax , ay )
* PBR_SmithGGXAniso( nDotV , dot( camDir , tangent ) ,
dot( camDir , bitangent ) , ax , ay );
vec3 Fs = mix( cSpecular , vec3(1) , FH );
return nDotL * ( ( ( 1 / PI )
* mix( Fd , ss , material.subsurface )
* material.cAlbedo /* + Fsheen */)
* pow( 1 - material.metallic , 3 )
+ clamp( Gs , 0 , 1 ) * Fs * Ds );
}