[Android target]How to make SDLSurface(java) bg transparent?

Hello, everybody!
I’m writing extention under openfl. This is a haxe lib which has SDL backend in native platforms.
Could you please tell how to make transparent java view(SDLSurface class)background with sdl to have possibility see another android native view under it?
What changes must be done in cpp code(maybe some sdl attributes) and in java android tempate?
l’ll be appreciate for any help:)