OpenGL Interface in Windows NT 3.5

• Microsoft Windows NT Workstation version 3.5
• Microsoft Windows NT Server version 3.5

SUMMARY

This article defines and explains the OpenGL interface that is available and can be implemented in Windows NT version 3.5. The following topics are covered in this article:

• Definition of OpenGL
• Standards Organization
• Architectural Overview
• New API Functions
• Platform Compatibility

MORE INFORMATION

Definition of OpenGL

OpenGL is a software interface that allows graphics programmers to create high-quality three-dimensional color images with graphic effects such as shading, lighting, texture mapping and matrix transformations. OpenGL branched from the powerful IRIS GL graphics interface that runs on Silicon Graphics' IRIS GL workstations. While IRIS GL is platform- specific, OpenGL is an open standard designed to run on a variety of computers and a variety of operating systems.

Standards Organization

The OpenGL standard is maintained by an independent group called the Architectural Review Board (ARB), which meets on a quarterly basis and includes representatives from DEC, IBM, Intel, Silicon Graphics and Microsoft. The ARB governs both the features and conformance testing of OpenGL.

Architectural Overview

In Windows NT, GDI functions initiated from a graphics application are processed by the dynamic link library (DLL) GDI32.DLL on the client side. The GDI request is then transmitted to WINSRV.DLL on the server side. This in turn dispatches the requests to the video display driver through the device driver interface (DDI) layer called Win32 DDI.

OpenGL functions are processed the same way as GDI functions with a few additions. The functions are sent to OPENGL32.DLL on the client side for graphics processing. OpenGL requests are packaged and transmitted to WINSRV.DLL on the server side. The OpenGL requests are then dispatched to the video display driver through the hardware- specific DDI layer. The hardware-specific DDI resides alongside the Win32 DDI and can be obtained through a vendor that manufactures an OpenGL accelerator. If the accelerator is obtained, an additional software module known as the OpenGL Installable Client Driver is provided, which resides between OPENGL32.DLL and WINSRV.DLL.

New API Functions

OpenGL is basically a library of API functions for performing three- dimensional drawing and rendering. OpenGL adds five new categories of API functions to Windows NT. They are as follows:

• 115 OpenGL functions (prefixed with the letters GL)
• 43 utility functions (OpenGL utility library prefixed with GLU)
• 31 auxiliary functions (OpenGL auxiliary library prefixed with AUX)
• 6 WGL functions (prefixed with the letters WGL)
• 5 new Win32 API functions (no prefix)

Platform Compatibility

OpenGL functions are completely portable from one platform to another. However, porting an OpenGL application from one implementation to another involves some rewriting to accommodate differences in each platform running Windows NT version 3.5. In other words, OpenGL programs are not compatible at the binary level but are compatible at the source code level. Therefore these programs written and tested in one platform must be recompiled in others for it to run properly. Currently, OpenGL for Windows NT runs on Intel, Alpha, and MIPS platforms.

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