3D Graphics Programming with QuickDraw 3D 1.5.4

Extending QuickDraw 3D

QuickDraw 3D is designed to be easily extensible, so that you can, if necessary, add capabilities that are not part of the basic QuickDraw 3D feature set. For instance, you've already seen that QuickDraw 3D supplies two types of renderers, the wireframe and interactive renderers. The wireframe renderer creates line renderings of models, as illustrated in Figure 2 .

Figure 2 A model rendered by the wireframe renderer

The interactive renderer uses a more complex rendering algorithm that allows illumination and shading effects to be produced. Figure 3 shows the same teapot model rendered by the interactive renderer.

Figure 3 A model rendered by the interactive renderer

It's possible that some applications require even more complex rendering algorithms to render images adequately from a 3D model. For example, you might want to define a ray tracing renderer to support additional lighting effects such as reflection and refraction. In those cases, the application can define and register a custom renderer with QuickDraw 3D and then use that renderer in exactly the same way it would use any standard QuickDraw 3D renderer.

QuickDraw 3D is extensible in several ways:

You can define custom object types to augment the standard QuickDraw 3D object types.
You can define custom attributes and assign them to shapes or sets.
You can define custom shaders to create special shading effects or to handle any custom attributes you've defined. (The shaders that QuickDraw 3D supplies can handle all the predefined attribute types.)
You can define custom renderers to support other rendering algorithms.

In addition, QuickDraw 3D is designed to be portable to other software platforms and to support a variety of hardware accelerators:

QuickDraw 3D is cross-platform. It is available for the PowerPC version of the Mac OS and for the Microsoft Win32 API (running on either Windows 95 or on the Intel processor version of Windows NT 3.51 and later). This portability to other window systems is accomplished by isolating all window system-specific information into a layer called a draw context, which is associated with a view. QuickDraw 3D automatically handles system-dependent issues such as byte ordering.
QuickDraw 3D renderers can take advantage of hardware accelerators, if available.

Finally, QuickDraw 3D defines a platform-independent metafile (that is, a file format) for storing and interchanging 3D data. This metafile is intended to provide a standard format according to which applications can read and write 3D data, even applications that use 3D graphics systems other than QuickDraw 3D. QuickDraw 3D itself includes routines that you can use to read and write data in the metafile format. Apple Computer, Inc. also supplies a parser that you can use to read and write metafile data on operating systems that do not support QuickDraw 3D.

For further information about the metafile format, see 3D Metafile 1.5 Reference. This document is available online in the QuickDraw 3D 1.5 SDK.

Figure 4 shows the functional components of QuickDraw 3D.

Figure 4 The parts of QuickDraw 3D