Drawing Engines

A drawing engine is a plug-in software module that accepts drawing commands and produces a rasterized image. QuickDraw 3D RAVE is designed to make it easy for you to add drawing engines to those already available. When you register a drawing engine, it thereby becomes available for use by any application or system software running on a Macintosh computer.

QuickDraw 3D RAVE expects that a drawing engine will have a certain minimum set of required features and possibly one or more optional features. Every drawing engine must provide these features:

hidden surface removal (usually accomplished using z buffering with at least 16 bits per pixel)
point and line drawing, with application-specifiable point and line widths
drawing of Gouraud-shaded triangles
drawing of bitmaps having depths of 1, 16, or 32 bits per pixel
support for double buffering

In addition to the required features, a drawing engine may support one or more of these optional features:

high-precision hidden surface removal (using z buffering with at least 24 bits per pixel)
perspective-corrected hidden surface removal
texture mapping
triangle meshes (a memory and time optimization that allows rendered triangles to share vertices)
transparency blending, with or without an alpha channel
antialiasing
z-sorted rendering of non-opaque objects
support for OpenGL features (such as scissoring, multiple blending modes, area and line stipple patterns, and so forth)

The interactive renderer supplied as part of QuickDraw 3D uses a software-only drawing engine that can draw to any available device. In addition to the required features listed earlier, the drawing engine supplied with the interactive renderer supports these optional features:

z buffering with 16 or 32 bits per pixel
direct rendering at 16 or 32 bits per pixel (rendering at fewer than 16 bits per pixel is also supported, but with lower performance)
perspective-corrected texture mapping

It's important to keep in mind that a drawing engine is a low-level 3D driver and hence does not support some features found in higher-level interfaces. The current programming interfaces to drawing engines do not support any of these features:

transformations, shading, or clipping
I/O support (such as reading and writing 3D metafiles)
high-level primitives (such as curved surfaces)
support for drawing to windows that straddle two or more devices

Because of these limitations, most applications should not use QuickDraw 3D RAVE directly. Instead, you should use the high-level programming interfaces provided by QuickDraw 3D or other system software that provides 3D capabilities.

QuickDraw 3D RAVE does not require that a drawing engine be capable of drawing to all devices available on a particular computer. Rather, a particular drawing engine may support only a single output device. For example, a drawing engine that uses a frame buffer's built-in 3D acceleration hardware may be incapable of rendering to any other device. As a result, QuickDraw 3D RAVE won't allow some other device to be associated with that drawing engine. This means that QuickDraw 3D RAVE does not provide automatic support for drawing into windows that cross multiple devices. Instead, it is the application's responsibility to determine when a window does straddle devices and to construct multiple draw contexts (described next) for the output image.

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