x-windowsp.k.k.thambi the x window system module 5

X-WindowsP.K.K.Thambi

The X Window System

Module 5


X Window System

The X Window system was developed as part of Project Athena at MIT. In 1987, X Version 11 is released. X is now controlled and maintained by the Open Group.

The X Windows System, also referred to as ‘X’ or “X11”, is the standard graphical engine for Unix , Linux and Sun workstations.

It is largely OS and hardware independent, it is network-transparent, and it supports many different desktops.


The Graphic User Interface in X

X Window uses a bit-mapped display where each pixel can be manipulated individually.

The entire display is known as the root window, and individual applications are displayed as windows on this root window.

X is started with the startx or xinit commands. – X can also be invoked during system startup


X-window Screen


Client / Server Architecture

Separate programs that talks together for a specific aim.

Server will be the program that supplies the services and the client is who make the requests.


X Window Clients and Servers

Although you can easily use the X Window system to run programs stored on your local computer, you can also run applications over the network

X Window uses a client/server model in which a program can run on one computer but display its output on another

The desktop system from which you run a program is called the X server, the system that hosts and executes the program is called the X client (this is opposite of normal networking)


X Protocol

Based on TCP/IP stackThe X Protocol provides a client-server architecture at the application level:

The X client is the processing part of the application and often runs on a remote machine.

The X server is the display and interaction system.


X Protocol cont’d

The X Protocol is also divided into device dependent and device independent layers.


X architecture

The client-server nature of the X Protocol allows a single X server to support many clients (applications) on several hosts.


Client-Server Window System

Application 1 Application 2 Application nClient ApplicationPrograms

Virtualdisplay 1

Virtualdisplay n

Resourceallocator

Devicedriver

Window2 Window

n

Window1

MouseKeyboard

(After Fig 10.2, Dix, Finlay, Abowd and Beale)

Virtualdisplay 2

Server

Devices

Device-independent abstraction level

Translates abstraction into reality:one per terminal type

Could beWindowManager


X Server Design Device Dependent Layer

– It is this layer that is responsible for localizing the X server to the native environment, be it Windows NT or Solaris.

– This layer swaps bytes of data from machines with differing byte ordering. Byte ordering (MSB and LSB) is noted in each X request.

– This layer hides the architectural differences in hardware and operating systems.

– Maintains device driver dependencies for keyboard, mouse and video.


X Server

The X server therefore: displays drawing requests on the screen. replies to information requests. reports an error in a request. Manages the keyboard, mouse and display

device. – Multiplexes keyboard and mouse input onto the

network (or via local IPC) to the respective X clients. (X events)

creates, maps and destroys windows. – writes and draws in windows


X Client

• sends requests to the server. • receives events from server. • receives errors from the server


X Protocol

X client communicate with X server using the X protocol.

Data is exchanged in an asynchronous manner over a two-way communication path that enables transmission of a stream of 8 –bit bytes.

X protocol is the machine language for the X Window system


X Protocol messages

Requests – client sends requests to the server (e.g. create window)

Replies – server response to client requests

Events – server forwards events (such as mouse clicks or keyboard entry) to the client

Errors – server reports errors to the client


Protocol Messages - Requests

Requests X clients make requests to the X server for a

certain action to take place. i.e.: Create Window To enhance performance, the X client normally

does not expect nor wait for a response. The request is typically left to the reliable network layer to deliver.


Protocol Messages - Replies

Replies The X Server will respond to certain X client

requests that require a reply. As noted, not all requests require a reply.


Protocol Messages - Events

Events The X server will forward to the X client an event

that the application is expecting. This could include keyboard or mouse input. To minimize network traffic, only expected events are sent to X clients.

X events are 32 bytes


Protocol Messages - Errors

Errors The X server will report errors in requests to the X

client. Errors are like an event but are handled differently.

X errors are the same size as events to simplify their handling. They are sent to the error handling routine of the X client.


Xlib: The Assemble language of X

A set of C library of X window system Xlib gives you access to the X protocol through

more than 300 utility routines. It is the The Assemble language of X Window

System.


X Toolkit: The High level language of X

XToolkit Intrinsic (Xt Intrinsic) – an object- oriented approach to implement the basic

building blocks called widgets


Structure of an X application

X application

X toolkit

Xt intrinsic

Xlib

X protocol

X Server

Device- dependent Layer

X protocol

Network Interface

User

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