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LFCS 2012: X and Wayland
Posted Apr 19, 2012 22:00 UTC (Thu) by nybble41 (subscriber, #55106)
What we need is not a remote version of the Wayland protocol, which is inherently _local_ due to the use of shared memory, but general-purpose protocols for remote rendering and input, targeting Wayland for access to the hardware. For now, the X protocol can serve that purpose, as can single-window adaptations of VNC. Future protocols can take similar advantage of Wayland for the low-level hardware interfaces, and concentrate instead on remote rendering.
Posted Apr 22, 2012 16:48 UTC (Sun) by VITTUIX-MAN (guest, #82895)
This does all the things we love in networked X, that is mainly rootlessness is the default and it would allow plugging into a running session, so connection problems would no longer close all open programs.
Posted Apr 22, 2012 17:16 UTC (Sun) by renox (subscriber, #23785)
For LAN yes, but as I said here (http://lwn.net/Articles/493461/), WAN will probably suck unless there are many changes.
In my understanding currently:
- the stock server (Weston) doesn't know when a user moves/resizes a window until the client tells it, so there must be a round trip before any action happen: far from ideal in a WAN.
- Wayland has very limited server rendering, so to be able to have XRender-way to display text, you'd have to change it significantly, until then Wayland will use much more bandwith to display text than X (if the toolkit use the XRender extension of course).
Posted Apr 20, 2012 7:30 UTC (Fri) by renox (subscriber, #23785)
Except that it isn't possible to have network transparency which works well in a WAN with Wayland, without changing radically how Wayland works.
-Wayland developpers prefer CSD decoration: think about what this imply in term of latency when you want to move a window in a WAN vs server side management of windows.
-Also an X client can send an image of each letter only once on the server, cache it there, and then reuse it: very efficient in terms of bandwith usage, but currently Wayland don't provide this and as nybble41 said, it would be a big change to add a remote rendering protocol.
Posted Apr 20, 2012 9:56 UTC (Fri) by cortana (subscriber, #24596)
Posted Apr 20, 2012 11:45 UTC (Fri) by renox (subscriber, #23785)
Posted Apr 20, 2012 12:04 UTC (Fri) by chris.wilson (subscriber, #42619)
In contrast, the core protocol differs in that the server renders the glyph images itself, and so has a fixed concepts of fonts and glyphs and needs to inform the client of the font/glyph metrics, and in the various semantics of the operators and patterns. That the core fonts were only bitmaps and so were easier for hardware to implement and are still faster than compositing glyphs using Render, is an implementation detail.
Posted Apr 20, 2012 18:26 UTC (Fri) by raven667 (subscriber, #5198)
I really doubt that's true, maybe you are unfamiliar with remote rendering protocols other than X?
> Wayland developpers prefer CSD decoration: think about what this imply in term of latency when you want to move a window in a WAN vs server side management of windows.
I don't think client side decorations have anything to do with window management and I can't envision the problem you seem to be describing. I can't see how window move performance would be affected based on which process is drawing the border, in either case you have a rectangle that needs to be moved around. In fact I would expect the client side decorations to be faster because the current X architecture where window management and borders are in the same process requires extra round trips and coordination between the application, X and the window manger to make sure the borders are adjacent and not overlapping the window contents as it is being moved. This architecture also causes a lot of tearing, as the window contents and window border are drawn at different times by different apps.
> Also an X client can send an image of each letter only once on the server, cache it there, and then reuse it
As the people who are designing wayland (primarily a display protocol for local apps) are also the ones who designed the font caching you describe I think they can figure out how to make an efficient remote protocol if they apply themselves to it 8-)
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