Clients reading their surface position on screen

[Christopher James Halse Rogers]

On Tue, Aug 12, 2014 at 12:33 PM, Daniel van Vugt 
<daniel.van.vugt at canonical.com> wrote:
> There is a 5th option which would satisfy more (not all) of the 
> people mentioned:
> 
> 5. Shell mediates if a client has permission to ask for surface 
> coordinates. The API is restricted by default. The API _does_not_ 
> return the top-left corner of the surface. Instead it maps a local 
> surface coordinate (x,y) to screen coordinates (x',y'). This way we 
> can still map correct coordinates for arbitrary 3D transformations 
> (if we want to, but don't need to initially).

Again, this assumes that there exists a function whose domain is 
surface coordinates and range is screen coordinates. This function does 
not necessarily exist.

There *is* a unique mapping from screen coordinates to {surfaces} × 
(ℚ × ℚ), but (a) I don't think that's what AP is after - although 
it could implement it - and (b) it would require us to make all 
surfaces visible in some way to all clients.