LCA: The ways of Wayland

Posted Feb 14, 2013 16:55 UTC (Thu) by raven667 (subscriber, #5198)
In reply to: LCA: The ways of Wayland by nix
Parent article: LCA: The ways of Wayland

It seems that for the scrolling window case that there are several techniques which could be employed that would be faster than the degenerate case of repainting the whole buffer every frame such as detecting the motion and only sending changed portions or since "every frame is perfect" you could just throttle the number of frame updates sent by a fast changing window while still being completely responsive and without corrupting the output. This is the same kind of special case as redirecting compressed video streams straight through and decoding on the display side, implementing compression and acceleration techniques that are already known.

LCA: The ways of Wayland

Posted Feb 14, 2013 17:57 UTC (Thu) by nix (subscriber, #2304) [Link] (3 responses)

Have you ever tried to do interactive scrolling on a window with throttled updates? I have (while debugging Emacs scrolling). It is intolerable, very like driving with a variable lag in the steering.

Scrolling text efficiently is not best solved as a problem in general video compression: we know a lot about the nature of a scrolling window and can come up with very much better examples. (Proof by example: core text X scrolling back in the day, or X scrolling with XRender objects now that glyph cache defragmentation is implemented. It moves so fast that all you can see is a blur. I would consider it a very serious regression if it only updated a few times a second! Perhaps this doesn't matter much for xterms but it certainly matters for text editors. And I spend my whole day in one of those.)

LCA: The ways of Wayland

Posted Feb 14, 2013 18:33 UTC (Thu) by raven667 (subscriber, #5198) [Link] (1 responses)

What about capturing the PTY and redirecting it to a local terminal emulator? That should be the most performant, yes?

LCA: The ways of Wayland

Posted Feb 15, 2013 17:56 UTC (Fri) by nix (subscriber, #2304) [Link]

Hm, yeah, that would work. Feels like a disgusting kludge to have to start all connections locally and ssh out though, which is basically what you're suggesting. And if I want to start something graphical while I'm on the remote system, I'm SOL, which is a strict loss of functionality over today.

LCA: The ways of Wayland

Posted Feb 19, 2013 23:38 UTC (Tue) by raven667 (subscriber, #5198) [Link]

I was thinking about this and just did some very informal testing with the VNC implementation that comes with stock Mac OS X Screen Sharing and was able to remote a large terminal running "find /" to my laptop over wireless at home with very acceptable performance. There was at most 100ms of latency from hitting ctrl-c and having the output stop and the output was updating very quickly. Looking at my network stats it hit a peak of 2300 packets per second and 3MB/sec, the network latency between the devices is about 20ms. So what current implementation do seems to be OK at least as far as I'm concerned, at least with the latencies and bandwidth I have available at home 8-).