But can the client in HTTP/2 send more data to the server after it has received something, without having to send a full HTTP request? If not, I don't see how s

But can the client in HTTP/2 send more data to the server after it has received something, without having to send a full HTTP request? If not, I don't see how something like agar.io, which requires constant updates to the server on every mouse movement, can work without tremendous header overhead.