Intro(D4nfb)

Intro -- X Link Kit data structures and files

Description

This section describes the X Link kit data structures and files. X resources are data structures inside the server. Client applications create and manipulate these structures according to the rules established by the X protocol. Clients refer to these objects or resources with resource IDs which are 32 bit integers. Within the server they are C structures and are referred to by pointers.

The SCO X Server Link Kit eliminates the need to understand how clients establish connections with the server or how they access resources in the server. Instead, developers only need to concern themselves with the server's resource data structures and the pointers that provide access to them.

DDX

The DDX (Device Dependant X) layer has several kinds of resources, including windows, pixmaps, screens, devices, colormaps, fonts, cursors, and graphics contexts. The type names of the more important server structures usually end in ``Rec'' (short for record, for example, DeviceRec); the pointer types usually end in ``Ptr'', (for example, DevicePtr).

The structures and important defined constants are declared in header files that have names that suggest the name of the object. For example, there are two header files for windows. windows.h defines the minimal amount of information needed to use windows resources; windowstr.h defines the structures with all of their components in great detail for those who need it.

Most of the header files referred to in this section are found in:

../xlink/Xserver/include
../xlink/Xserver/hw/sco/ports

This directory structure assumes that ../xlink is the root of the X Link Kit filesystem.

These structures have three types of members:

attribute fields (structure fields that contain values)
pointers to procedures that operate on the object
a private field (or two) used by your DDX code to keep private data (typically, a pointer to another data structure).

DIX

DIX (Device Independent X) makes calls through pointers to procedures to do its tasks. These procedures are set either directly or indirectly by DDX procedures. Most of the procedures described in section D3nfb are accessed through one of these structures.

For example, the procedure to create a pixmap is attached to a ScreenRec(D4nfb) structure and can be called by the expression:

(* pScreen->CreatePixmap) (pScreen, width, height, depth);

NOTE: All procedure pointers must be set to some routine unless otherwise noted; a NULL pointer has unfortunate consequences. The SCO Server Link Kit supplies the NoopDDA(D3nfb) no-op procedure that you can assign to procedure pointers when they are not used.

Procedure routines are indicated in this documentation by this convention:

   void pScreen->MyScreenRoutine(arg0, arg1 ...)

A free routine (meaning it is not in a data structure) looks like this:

   void MyFreeRoutine(arg0, arg1, ...)

The attribute fields are mostly set by the DIX layer; the DDX should not modify them unless otherwise noted.