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Software to code Doom almost entirely in C, freeing the developers to think at a higher level and implement more features more rapidly.
Chapter 3 is entirely new because id Software used an entirely different development environment for Doom. Instead of developing everything on unstable DOS PCs, they took the chance on using expensive NeXT workstations. Even a fairly basic NeXTstation cost $4,995 in 1991, and a NeXTcube ran $12,395! It turned out to be worth it, though, because these workstations were rock-solid and allowed John Carmack and the other developers to make incredible progress instead of constantly fighting with crashing machines and a poor development environment. This chapter did a great job going through the architecture and benefits of the NeXT systems, and how id Software used them to full effect.
The next chapter was about the team and tools, like chapter 3 in the Wolfenstein 3D book. Things had changed dramatically, with the team moving to Dallas, TX and growing to fourteen people by the end of development. The tools were evolving, too, with some of the character sprites and animation done using stop motion capture, and the map editor (DoomED) taking on new features to support the multitude of new capabilities in the game engine. Walls in the game no longer needed to be orthogonal, although they still had to be vertical for rendering to be fast enough. Floors and ceilings could change height to create steps, platforms, and other environmental features. Various kinds of traps and ambushes were also possible now. It's quite amazing how many features were added to idTech 1 when compared to the Wolf3D engine. These new features, especially the non-orthogonal walls and varying heights, required a more efficient data structure for the maps, and the BSP (Binary Space Partitioning) node tree was commandeered for the job
Nearly half of the book is taken up by chapter 5 on the idTech 1 game engine. This chapter is just a monster of awesome information about the engine. It goes through every detail from the game tic design and use of fixed-point arithmetic to sound propagation and enemy AI. The section on the 3D renderer was especially interesting and detailed. There are great explanations on how the environment was drawn with its additional complexity, texture mapping with perspective correction, sprite clipping and animation, and diminished lighting to give the game its intense horror movie feel. This renderer section in particular was so interesting that it made me want to go implement a bunch of the algorithms myself just to be able to recreate them and see them in action. It looks like it would be immensely satisfying.
The last chapter described in fairly good detail how a number of ports of Doom were done on other game consoles. The console ports included the Atari Jaguar, Sega 32X, Super Nintendo, Sony PlayStation, 3DO, and Sega Saturn, and both the system architectures and Doom engine implementations are described. I was in high school during this era of the great console wars, although I never played Doom on any of them, just the excellent experience of the PC. I had forgotten how different these console architectures were, and some of the design decisions that went into those systems were truly remarkable...and strange. The sections on the Super Nintendo and PlayStation ports were my favorites. The Super Nintendo would have never been able to run Doom on its own, but with the extra power of the SuperFX chip that was used in Star Fox and a few other games, it was able to pull it off reasonably well. The PlayStation port was the most faithful of the ports, and even added some cool new features like colored ambient lighting. Of all of these systems, the PlayStation was exceptionally powerful for making great games. Even though other systems might have looked more powerful on paper, they all had disadvantages and unfortunate design decisions that handicapped them while the PlayStation was so easy to develop for that its potential could consistently be achieved in practice.
I enjoyed this book as much, if not more than the Wolf3D Black Book. From the beautiful full-color pictures to the detailed explanations of technical feature implementations to the well-chosen code listings sprinkled throughout the book, this was an incredibly fun guided tour of a legendary game engine. I devoured this book, and through it all, I wanted to do two things: go back and play through Doom again and re-implement some of those rendering algorithms for myself. I can't think of higher praise for a book, so if you've ever played Doom and want to know how it works, you need to go treat yourself to this book and the Wolfenstein 3D Black Book, too.
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