Structure

• Graphics drivers should be written in the C Programming Language.

• Use static variables rather than extern variables as much as possible. Any externally visible driver symbols, including global variables and structure names should be prefixed with the driver's name prefix. This makes them easier to identify and greatly reduces the risk of having two entities with the same name from different drivers.

• Do not depend on static data.

• Never use global variables for data that your driver needs to access from several routines. Instead, use Screen Privates. See ``Screen Private''.

• Use the NFB API for as much of the driver implementation as possible. In addition to simplifying the work, this increases the portability of the driver to future operating system platforms.

• Use #define values instead of hard-coded values as much as possible. In most cases, these should be defined in a driver-specific header file rather than in the driver code itself. Be sure include comments explaining each #define value in the header file.

• Driver source and the resulting binary code must have no external product dependencies other than the base operating system, development system, and the Hardware/Driver Developer's Kit.

• Define macros for drawing, clipping, and similar operations.

• For SVR5 and SCO OpenServer 5 NFB drivers, adapter-specific code belongs in a grafinfo(DSP/4dsp) file and not in the graphics driver itself. Graphics drivers should support the features of the chip set and use the grafquery(D3nfb) functions to read the grafinfo file for adapter-specific information.

  AIX 5L NFB drivers must code much of the adapter-specific information directly in the driver because they do not use a true grafinfo file. Instead, AIX 5L drivers use NFB_GRAFINFO driver definitions that are added to the ODM database. See ``Adding driver configuration parameters to the AIX 5L ODM database'' for more information about setting this up.

• For SVR5 and SCO OpenServer 5 NFB drivers, use the video BIOS implementation if available. Most graphics hardware for Intel machines comes with a video BIOS. Using this video BIOS to initialize the graphics card alleviates one of the most difficult tasks involved in getting your driver to run.