I would like to pre-render horizon of large landscape to texture and than paste it as cylindrical screen around the camera (to accelerate rendering of distant details)
Easiest would be make 8-gon screen uv-mapped to 4096x512 pixel frambuffer texture and render from 8 angles of camera with frustum 360/8=45 degrees wide (each angle mapped to different tile of framebuffer texture).
But as far as I know output framebuffer texture is always mapped to whole framebuffer i.e. to whole camera frustrum. Is that right? Is there a way how to choose mapping for frambuffer output texture?