[SDL] Sharing a surface

[Brian Edmond]

Is there a way for 2 applications (distinct processes) to share a surface.  So 
can I do something like the following:

App 1 creates a surface and renders to it.
App 2 creates a surface and renders to it.
App 3 then takes both of the above surface and blits them together with a 
blend to the main display, composites the apps together.

This means App 3 needs to reference the surfaces in the other apps.  These 
would be HW surfaces.

Thanks,
Brian