[Dev] Display servers (was Cynara)

Carsten Haitzler (The Rasterman) tizen at rasterman.com
Sat Apr 12 03:21:44 GMT 2014


On Fri, 11 Apr 2014 16:01:11 +0300 Jussi Laako <jussi.laako at linux.intel.com>
said:

> Speaking of display server's I find it hilarious that keyboard, touch, 
> mouse and video output somehow belong together, but audio is always 
> outside the picture.

historical artifact, and actually ncd  back in the 90's merged them - look up
NAS. they added audio protocol to their x11 terminals because they now added
the hardware. before that xterminals and pcs at most did beeps. that's all the
hw did. beep controls are actually embedded in x11 protocol, so this was added.
it didn't catch on though. so it's a historical artifact and also just that the
graphics guys did input but didn't do audio - they just never were audio people.

> Does Siri voice input in iOS go through display server? I don't think so.
> 
> Why would audio be somehow special compared to touch, mouse, keyboard or 
> video? How about haptic feedback or accelerometers?

it isn't. it's just a historical artifact we live with. if the display server
is determining things like location of window, visibility of it, etc. i would
imagine it should also have a say in audio routing - eg audio of an app is
muted if it is hidden (unless app request a grab on audio ala grab on keys).
that volume of audio from that app should vary with window stacking maybe?
above == louder ... etc.

> In Tizen, pulseaudio is audio equivalent of the display server. Why 
> doesn't pulseaudio hook into all keyboard, mouse and touch events?

because it doesn't need them. the display server does.

> Better to keep all those separate and not create "all encompassing" mega 
> notreally-display -server that would be security and privacy disaster.

too late. input is tied to its visual representation and that representation is
decided by the display server, so it decided input transforms and routing.
pulse audio doesnt need input because it doesnt auto control audio via input
devices, it doesnt provide input feedback to pluse audio clients. a display
server does. a display server lets you share the keyboard, mouse etc. and the
screen.

-- 
Carsten Haitzler (The Rasterman) <tizen at rasterman.com>


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