[PATCH v2 wayland 1/2] protocol: Add a request and event to identify the visible area for a surface

[Bill Spitzak]

Scott Moreau wrote:

> Wouldn't a client then be able to compute its absolute position in 
> global coordinates using this protocol and the output information?

Not if the compositor returns something other than the output's bounds 
for the clipping, for instance it could remove the area covered by a 
panel or other popups.

> In 
> any case, I'm not sure this makes sense as a whole. It seems there would 
> be a tendency for clients to use the probe request repeatedly to find 
> the information it wants. Is there a problem communicating the type of 
> surface so the compositor can place it?

Because the method for computing a new position for the popup can be 
arbitrarily complex and this would require the client to send an entire 
program to the compositor.

For example: popup a menu in a position so that all submenus (even 
though they are not yet displayed) will not be clipped. The relative 
positions of submenus to the parent menu will be altered depending on 
what fits, too (for instance if the entire cascade does not fit, some 
will be placed on the opposite side of their parent to make a zig-zag 
cascade).