struct T_BPMaterial
{
	vec3 cAlbedo, cSpecular;
	float specPower , ambient;
};


vec3 BP_Shade(
		in T_BPMaterial material ,
		in vec3 rayDir ,
		in vec3 normal ,
		in vec3 lightDir )
{
	const vec3 halfVec = normalize( rayDir + lightDir );
	const float nDotL = dot( normal , lightDir ) ,
		nDotH = dot( normal , halfVec ) ,
		si = pow( clamp( nDotH , 0 , 1 ) , material.specPower ) ,
		di = material.ambient + ( 1 - material.ambient )
			* clamp( nDotL , 0 , 1 );
	return mix( material.cAlbedo * di , material.cSpecular , si );
}