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Code Review of Doom For the iPhone
Developer Fabien Sanglard has written a code review for id Software's iPhone port of Doom. It's an interesting look into how the original 1993 game (which he also reviewed to understand its rendering process) was adapted to a modern platform.
"Just like Wolfenstein 3D, Doom was rendering a screenframe pixel per pixel. The only way to do this on iPhone with an acceptable framerate would be to use CoreSurface/CoreSurface.h framework. But it is unfortunately restricted and using it would prevent distribution on the AppStore. The only solution is to use OpenGL, but this comes with a few challenges: Doom was faking 3D with a 2D map. OpenGL needs real 3D vertices. More than 3D vertices, OpenGL needs data to be sent as triangles (among other things because they are easy to rasterize). But Doom sectors were made of arbitrary forms. Doom 1993's perspective was also faked, it was actually closer to an orthogonal projection than a perspective projection. Doom was using VGA palette indexing to perform special effect (red for damage, silver for invulnerable...)."
I remember playing Doom in the mid-90's on my friend's Gateway 2000 Pentium 100Mhz. I still play it to this day from time to time (openGL port on Linux). It's mindless, self-indulging, gory, non-challenging (now, not then!), and it's becoming one of timeless those FPS games that won't die because it's story line is simple and not drug out, you're thrown right into the mix and you can keep your objective as simple as you want: Make it to the end of the map.