Thanks pq. It is helpful for me. I will have a try with your idea. :)

-----Original Message-----
From: Pekka Paalanen [mailto:[email protected]] 
Sent: Saturday, February 08, 2014 5:56 PM
To: Wang, Quanxian
Cc: [email protected]
Subject: Re: Is there any way to let compositor set the data in client space 
and then return back to client?

On Sat, 8 Feb 2014 08:19:06 +0000
"Wang, Quanxian" <[email protected]> wrote:

> Hi, All
> 
> I want to allocate some space in client, and let compositor set some 
> data in this space and then return back to client.
> 
> It seems like user data mechanism.
> 
> Any way to implement that?

Not really, it's nothing like user data.

You have to make the client bind to a new protocol interface you designed, and 
then use events to pass the data to the client.

If you need to pass significant amounts of data, you can use a mechanism 
similar to passing XKB keymaps, see wl_keyboard.keymap event. There the 
compositor creates the shm file. If you want the shm file created by the 
client, you pass the file descriptor in the other direction, similar to 
wl_shm.create_pool, have the server fill out the memory, and then send an event 
to say it's done or rely on a wl_display.sync roundtrip.


Thanks,
pq
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