[PATCH wayland 1/2 v2] protocol: Add resize from center flag.

[Bill Spitzak]

Scott Moreau wrote:

> Now that you mention it, I believe I have seen this used somewhere too 
> and it makes sense. As a side note, the algorithm is always the same for 
> resize-from-center regardless if it's horizontal, vertical or both.

I was imagining "resize from center horizontal" would only move the left 
and right edges, and "resize from center vertical" would only move the 
top and bottom edges.

Not sure if it is useful but it seems consistent.