[techtalk] GUI's

Jeff Dike jdike at karaya.com
Wed Oct 20 16:22:19 EST 1999


coolian at thecia.net said:
> >Do they layer on top of the X-windows environment? What is their use?
> >Is there someplace someone could direct me to learn more about this?

> Tell me about it. I still don't get it.

There is a set of layers that looks like this (usually):

	Sessions
	Applications
	Toolkits
	Xlib
	....
	X server

The X server is something that sits out on the net controlling a display.  Its 
main functions are to deal with windows and draw things in them and send user 
input back to the applications(but there are a whole lot of complications 
having to do with keeping network round-trips to a minimum, which helps 
performance).

Xlib is on the other side (the application side) of the network connection.  
Its job is mainly to turn X API calls into the wire protocol and send them to 
the X server.

X Toolkits provide the basic building blocks of an application.  A toolkit 
usually provides interfaces to create a coherent (visually and behaviorally) 
UI.  This includes things like menus, workareas, dialog boxes, etc.  It also 
includes protocols for behavior that all applications are expected to support, 
like cut-and-paste, and drag-and-drop.  Examples include Qt (the KDE toolkit), 
gtk (Gnome), Xt (the original X toolkit), dwt (DECWindows), ol (OpenLook).

Applications are the things that provide some kind of useful (usually) 
function.
Window managers are a specialized application, but there's nothing 
particularly special about them.

Sessions are a group of applications and their state.  A session manager may 
do things like start up a particular set of apps, and shut them all down again 
after telling them to save their state.

Gnome and KDE are overarching projects which encompass a toolkit, a set of 
applications, and a session manager.

				Jeff



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