Apple's Implementation

OpenGL itself is a hardware-independent API that provides no support for windowing tasks or obtaining user input. Apple's implementation provides four APIs for working with OpenGL:

• NSGL, for use with the object-oriented Cocoa application environment

• the AppleGL Library (AGL), for use with the procedural Carbon application environment

• CGL (the core OpenGL API), for use with full-screen graphics applications only

• the OpenGL Utility Toolkit (GLUT), for use with legacy GLUT code

Since you are porting your C or procedural C++ code to Mac OS X, you will probably want to investigate the AGL API. It is a higher-level API that enables you to do graphics rendering inside a window. AGL automatically loads the necessary libraries for the routines that your application uses, as well as enabling you to choose the best renderer for a given pixel format. If you wish, you can select specific renderers or specify criteria by which the renderer is chosen. AGL also handles the choosing of renderers when a graphics image spans multiple monitors.

Porting Notes

Be aware that OpenGL does not allow direct access to any of its frame buffers. Instead, you must use the appropriate OpenGL functions, such as glReadPixels, to read the frame buffer into system memory. Apple has optimized the routines that access and work with OpenGL, and these routines provide higher performance than most programmers could achieve even if they had direct access to the OpenGL frame buffers.

OpenGL is a cross-platform standard, but be aware that not all hardware renderers support all the OpenGL extensions. At run time, applications must check the OpenGL version or extensions string for the current renderer to determine what features the current renderer supports.

Mac OS X version 10.2 (Jaguar) supports 33 new OpenGL extensions and includes a number of other improvements. You may want to require customers to have Mac OS X version 10.2 or later to run your application.

Since you are making your application cross-platform, consider using QuickTime to simplify your Win32 and Mac OS X code bases. QuickTime includes functions that enable you to open files in dozens of graphics formats. You can simplify your code on both platforms by using QuickTime to open texture files.

For Further Information

OpenGL is an open graphic standard implemented on Windows, Mac OS, Linux, and other platforms. The best web site for documentation, links, and other resources is the OpenGL web site, at http://www.opengl.org. In addition, you should use the resources listed below to get started with OpenGL on Mac OS X.