X Window System, Version 11 (X11)

The X Window System, Version 11 (X11), developed by the Massachusetts Institute of Technology (MIT) X Consortium includes the following specifications: the Xlib C Language Interface (Xlib), the X Toolkit Intrinsics C Language Interface (Xt), and the Bitmap Distribution Format 2.1 (BDF).

X11 is a network-based protocol. A client application can run on the same or different system from the server that controls the display. In this server-client model, the application (which may run on one machine) is referred to as the window client. The system on which the user-interface is displayed may be a different machine and is referred to as the display host or window server.

Window systems are usually based on a pixel imaging model or a stencil/paint imaging model. The imaging model layer of the windows architecture controls how the window system accesses the display. X11 uses a pixel-based (raster) model in which images are viewed as rectangular areas of device-dependent pixels.

The Xlib library routines communicate with the X11 server via the X protocol. Xlib is the lowest-level C language application programming interface (API) to the X protocol.

The main task of Xlib is to translate C data structures and procedures into X protocol events; it sends them off and receives protocol packets in return that are unpacked into C data structures. Xlib provides full access to the capabilities of the X protocol but does little to make programming easier. It handles the interface between an application and the network and includes some optimizations that encourage efficient network usage.

Because application development at the Xlib level can be tedious, MIT developed the X toolkit, Xt. The designers of Xt were aware that the toolkit would need to support a variety of graphical user interface standards. For this reason, Xt was divided into two portions. The first portion is a prebuilt set of user interface components known as widgets. The second portion is the programmer interface for manipulating widgets, known as intrinsics.

Although it is device-independent, X11 allows an application to tailor itself to the hardware on which it is run.

PostScript Language

The PostScript^(TM) language, from Adobe Systems Inc., is the modern standard for electronic printing. The first edition of the PostScript Language Reference Manual, published in 1985 by Addison and Wesley, established PostScript Level One. Today, PostScript is supported as a standard by all major computer, printer and imagesetter vendors.

Numerous extensions were requested by the industry, so, in 1990, the second edition of the reference manual was published. It describes three major extensions to PostScript Level One: (1) An extension to deal with color output, (2) A composite font model, mainly used for very large fonts (for example, Asian languages) and (3) A set of extensions for screen output, called the Display PostScript^(TM) system, or DPS. DPS displays graphical information on the computer screen with the same imaging model and PostScript language that are the standards for printers and typesetters.

These major extensions and a large number of minor ones comprise PostScript Level Two, often referred to as PS2 or PSL2.

Solaris Compliance With X11

OpenWindows consists of the OpenWindows server, the Display PostScript^(TM) (DPS) extension support, the OpenFonts^(TM) Technology, the OPEN LOOK window manager (olwm), the XView Toolkit, the OPEN LOOK Intrinsics Toolkit (OLIT), the DeskSet^(TM) tools, and demonstration applications.

The OpenWindows server and the associated X libraries, which include Xlib and Xt, are compliant with X11, Release 5.

The OPEN LOOK Intrinsics Toolkit API is an implementation of MIT's Xt toolkit with an OPEN LOOK widget set. AT&T created the OPEN LOOK Intrinsics Toolkit by building a set of widgets for Xt that conform to the OPEN LOOK GUI specification.

The XView toolkit (X Window System-based Visual/Integrated Environment for Workstations) is a C-language toolkit providing a rich set of components for building applications. Like the Intrinsics, XView is built on Xlib. SunSoft has made the source code to the XView Toolkit freely available. It is shipped as part of the standard MIT X distribution and with UNIX System V Release 4.

OpenWindows, through the OPEN LOOK window manager, fully supports the X11 Inter-Client Communications Conventions (ICCC) as defined in X11 Release 5. The ICCC manual provides basic policy intentionally omitted from X itself, such as rules for transferring data between applications, transfer of keyboard focus, layout schemes, colormap installation and other features.

Solaris Compliance with PostScript

The OpenWindows server is a complete implementation of PostScript Level Two. The Display PostScript system is implemented as an extension to the X Window System and includes the following enhancements:

• Support for F3 Latin and Asian fonts
• Support for obtaining prescaled bitmap font formats from X11 font code

X11 Specification and Related Publications

The first publication listed below defines the X11 protocol specification; it is also defined in subsequent supplements supplied with X11 Release 5.

• X Window System Third Edition, Schiefler & Gettys, Digital Press, 1992

• XView Programming Manual, O'Reilly & Associates, Inc., 1989
• XView Reference Manual, O'Reilly & Associates, Inc.
• PostScript Language Reference Manual, Second Edition, Addison-Wesley
• XView Developer's Notes, Sun Microsystems, Inc.
• OpenWindows Reference Manual, Sun Microsystems, Inc.
• Desktop Integration Guide, Sun Microsystems, Inc.