public Helix.Material CreateMaterial(IGeometryMaterial mat, out bool isTransparent)
        {
            var diffuseTexture = ReadTexture(mat);

            if (diffuseTexture == null)
            {
                isTransparent = false;
                return(ErrorMaterial);
            }

            var material = new Helix.DiffuseMaterial
            {
                DiffuseMap = diffuseTexture
            };

            material.Freeze();
            isTransparent = mat.Flags.HasFlag(MaterialFlags.Transparent);
            return(material);
        }