public static extern void cdo_render_sink(cdo_int_rclbck_t rclbck,
     CDOH handle, IntPtr opaque, ref CDORenderRequest request);
 internal static CDORenderRequest toNative(RenderOptions options)
 {
     CDORenderRequest result = new CDORenderRequest();
     result.sinkId = StringHelper.toNative(options.sinkId);
     result.mirror = options.mirror;
     result.filter = StringHelper.toNative(options.filter.StringValue);
     result.opaque = IntPtr.Zero;
     return result;
 }