#include "luminance.glsllib"

#ifndef scatter_reflect
#define scatter_reflect           0
#define scatter_transmit          1
#define scatter_reflect_transmit  2
#endif

vec4 specularBSDF(in vec3 N, in vec3 L, in vec3 viewDir, in vec3 lightSpecular,
                  in float ior, in float shininess, in vec3 tint, int mode)
{
    vec4 rgba = vec4( 0.0, 0.0, 0.0, 1.0 );
    float cosTheta = dot( N, L );
    if ( 0.0 < cosTheta )
    {
        if ( ( mode == scatter_reflect ) || ( mode == scatter_reflect_transmit ) )
        {
            vec3 R = reflect( -L, N );
            float cosAlpha = max( 0.0, dot( R, viewDir ) );
            float shine = pow( cosAlpha, shininess );
            rgba.rgb = shine * lightSpecular;
        }
    }
    if ( ( mode == scatter_transmit ) || ( mode == scatter_reflect_transmit ) )
    {
        // check against total reflection
        vec3 R = refract( -viewDir, N, ior );
        if ( R == vec3( 0.0, 0.0, 0.0 ) )
        {
            rgba.a = 1.0;
        }
        else if ( mode == scatter_transmit )
        {
            rgba.a = 0.0;
        }
        else
        {
            rgba.a = 1.0 - luminance( tint );
        }
    }
    return( rgba );
}