Subsurface support, or delegated compositing

Christopher James Halse Rogers raof at
Mon Nov 25 23:40:07 UTC 2013

On Mon, 2013-11-25 at 15:00 +0800, Daniel van Vugt wrote:
> (a) What's the use-case for needing to synchronize parent/child 
> rendering? I'm thinking most use-cases don't need synchronization 
> between the two clients. The server already ensures there's always being 
> a buffer to render (without blocking) and without tearing.

Most usecases I can think of, yes.

Off the top of my head, having a frame-accurate count overlay on top of
video would be one use-case.

Another, probably more common, one would be animations involving the
parent/child interface - think expanding the size of the embedded area.

> (b) Why wouldn't we just deliver input to whatever is on top and 
> handling input? Any events not handled by the child/subsurface can work 
> down the stack (to the parent and beyond). Although I don't think we 
> have the client API ability yet to designate an "input area" or to tell 
> the server to replay events to the lower level.

Right. We wouldn't do this now because we don't have any ability to do
this now :).

And this obviously only works if the model *is* a stack, which I don't
believe it will be in general; it'll be a tree. An obvious example is a
browser window with two different pieces of flash embedded.
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