BRDFLafortuneFitting.Program.std_coords_to_half_diff_coords C# (CSharp) Method

        static void std_coords_to_half_diff_coords( double _ThetaIn, double _PhiIn, double _ThetaOut, double _PhiOut,
													out double _ThetaHalf, out double _PhiHalf, out double _ThetaDiff, out double _PhiDiff )
        {
            // compute in vector
            double in_vec_z = Math.Cos(_ThetaIn);
            double proj_in_vec = Math.Sin(_ThetaIn);
            double in_vec_x = proj_in_vec*Math.Cos(_PhiIn);
            double in_vec_y = proj_in_vec*Math.Sin(_PhiIn);
            In.Set( in_vec_x, in_vec_y, in_vec_z );

            // compute out vector
            double out_vec_z = Math.Cos(_ThetaOut);
            double proj_out_vec = Math.Sin(_ThetaOut);
            double out_vec_x = proj_out_vec*Math.Cos(_PhiOut);
            double out_vec_y = proj_out_vec*Math.Sin(_PhiOut);
            Out.Set( out_vec_x, out_vec_y, out_vec_z );

            // compute halfway vector
            Half.Set( in_vec_x + out_vec_x, in_vec_y + out_vec_y, in_vec_z + out_vec_z );
            Half.Normalize();

            // compute  _ThetaHalf, _PhiHalf
            _ThetaHalf = Math.Acos( Half.z );
            _PhiHalf = Math.Atan2( Half.y, Half.x );

            // Compute diff vector
            In.Rotate( ref Normal, -_PhiHalf, out Temp );
            Temp.Rotate( ref BiTangent, -_ThetaHalf, out Diff );

            // Compute _ThetaDiff, _PhiDiff
            _ThetaDiff = Math.Acos( Diff.z );
            _PhiDiff = Math.Atan2( Diff.y, Diff.x );
        }