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A New Animation Framework: X-Sharp

Listings 52.1 through 52.10 shown earlier represent not merely faster animation in library form, but also a nearly complete, extensible, data-driven animation framework. Whereas much of the earlier animation code I’ve presented in this book was hardwired to demonstrate certain concepts, this chapter’s code is intended to serve as the basis for a solid animation package. Objects are stored, in their entirety, in customizable structures; new structures can be devised for new sorts of objects. Drawing, preparing for drawing, and moving are all vectored functions, so that variations such as shading or texturing, or even radically different sorts of graphics objects, such as scaled bitmaps, could be supported. The cube initialization is entirely data driven; more or different cubes, or other sorts of convex polyhedrons, could be added by simply changing the initialization data in Listing 52.8.

Somewhere along the way in writing the material that became this section of the book, I realized that I had a generally useful animation package by the tail and gave it a name: X-Sharp. (X for Mode X, sharp because good animation looks sharp, and, well, who would want a flat animation package?)

Note that the X-Sharp library as presented in this chapter (and, indeed, in this book) is not a fully complete 3-D library. Movement is supported only along the Z axis in this chapter’s version, and then in a non-general fashion. More interesting movement isn’t supported at this point because of one of the two missing features in X-Sharp: hidden-surface removal. (The other missing feature is general 3-D clipping.) Without hidden surface removal, nothing can safely overlap. It would actually be easy enough to perform hidden-surface removal by keeping the cubes in different Z bands and drawing them back to front, but this gets into sorting and list issues, and is not a complete solution—and I’ve crammed as much as will fit into one chapter’s code, anyway.

I’m working toward a goal in this last section of the book, and there are many lessons to be learned and stories to be told along the way. So as X-Sharp grows, you’ll find its evolving implementations in the chapter subdirectories on the listings diskette. This chapter’s subdirectory, for example, contains the self-extracting archive file XSHARP14.EXE, (to extract its contents you simply run it as though it were a program) and the code in that archive is the code I’m speaking of specifically in this chapter, with all the limitations mentioned above. Chapter 53’s subdirectory, however, contains the file XSHARP15.EXE, which is the next step in the evolution of X-Sharp, and it is the version that I’ll be specifically talking about in that chapter. Later chapters will have their own implementations in their respective chapter subdirectories, in files of the form XSHARPxx.EXE, where xx is an ascending number indicating the version. The final and most recent X-Sharp version will be present in its own subdirectory called XSHARP22. If you’re intending to use X-Sharp in a real project, use the most recent version to be sure that you avail yourself of all new features and bug fixes.

Three Keys to Realtime Animation Performance

As of the previous chapter, we were at the point where we could rotate, move, and draw a solid cube in real time. Not too shabby...but the code I’m presenting in this chapter goes a bit further, rotating 12 solid cubes at an update rate of about 15 frames per second (fps) on a 20 MHz 386 with a slow VGA. That’s 12 transformation matrices, 72 polygons, and 96 vertices being handled in real time; not Star Wars, granted, but a giant step beyond a single cube. Run the program if you get a chance; you may be surprised at just how effective this level of animation is. I’d like to point out, in case anyone missed it, that this is fully general 3-D. I’m not using any shortcuts or tricks, like prestoring coordinates or pregenerating bitmaps; if you were to feed in different rotations or vertices, the animation would change accordingly.


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Graphics Programming Black Book © 2001 Michael Abrash