Server Architecture

Figure 2-1 illustrates the structure of the server. This diagram is an expansion of the OpenWindows Server architecture component in Figure 1-1 on page 2.

Figure 2-1

X11R5 Server

The X11R5 sample server from MIT was designed and implemented to be portable; it hides differences in the underlying hardware from applications, or clients. The server handles all drawing, interfaces with device drivers to receive input, and manages off-screen memory, fonts, cursors, and colormaps. The sample server contains the following parts, or layers:

• Device-Independent Layer (DIX)

  The DIX layer contains functions that do not depend on graphics hardware, input devices, or the host operating system--these functions are portable from one implementation to another. It dispatches client requests, manages the event queue, distributes events to clients, and manages visible data structures.

• Device-Dependent Layer (DDX)

  The DDX layer contains routines that depend on graphics hardware and input devices the server must accommodate. This layer is a major portion of the OpenWindows server, Sun's value-added product. This layer includes creating and manipulating pixmaps, clipping regions, colormaps, screens, fonts, and graphics contexts. In addition, the DDX layer collects events from input devices and relays them to the DIX layer.

• Operating System Layer (OS)

  The OS layer contains functions that depend on the host operating system. This layer is another part of Sun's value-added product. The OS layer manages client connections and connection authorization schemes, and provides routines for memory allocation and deallocation.

• Font Management Library

  The font management library enables the server to use font files of different formats and to load fonts from the X font server. The font features of the OpenWindows server are described in detail in Chapter 5, "Font Support."

MIT X Extensions

The X Window System is extensible; that is, new features and technology can be added easily. The OpenWindows server supports six X extensions as defined (or proposed) by the MIT X Consortium. For more information on the standard X Extension Mechanism, see The X Window System Server and the Xlib Programming Manual.

The OpenWindows server supports the following MIT extensions:

• XInput
• MBX (Multi-Buffering)
• SHAPE
• MIT-SHM (Shared Memory)

• XTEST
• MIT-SUNDRY-STANDARD

See "MIT X Extensions Supported" on page 21 for more information on these extensions.

DPS Extension

The DPS extension is implemented as an extension to the server. Clients send PostScript to the server via wraps. Data can be returned from the server to the client by specifying output arguments. The DPS client library implements DPS client-server communication transparently using the X protocol.

Applications that use the DPS extension create one or more contexts. A context can be thought of as a virtual printer, with its own stacks, input/output facilities, and memory space.

The interpreter schedules context execution. Each context has access to its private VM (virtual memory space). An additional common portion of VM space, called shared VM, is shared among all contexts and contains system fonts and other shared resources. Private VM can contain fonts private to the context.

See Chapter 4, "DPS Features and Enhancements" for more information on this extension.

Applications That Run With the Server

You can run the following kinds of applications with the server:

• Applications written with the following toolkits:

  · OpenWindows 3.3 toolkits: OLIT and XView

  · Motif toolkit

  · Xt toolkit

• Applications written for the X protocol
• Applications written for the DPS interface
• SPARC OpenWindows Version 3 X11 applications compiled under SunOS 4.x

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Note - The OpenWindows Version 3 X11 applications must adhere to the system Binary Compatibility Package. See the Solaris Binary Compatibility Guide for more information.

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• x86 Applications from Interactive Unix.

Applications written with the following interfaces are not supported:

• TNT, NeWS, and XVPS
• SunView, SunWindows, and Pixrect