Wolfenstein 3D IS technically possible on stock A500 shocker!

[commodorejohn]

Yeah, it's frankly amazing that anybody got 3D games running on the Genesis at all - it pushes tiles and sprites beautifully, but tile-oriented 3D rendering is at least as terrible as planar 3D rendering. I don't doubt that it's possible to run Wolf3D on a 500 (given sufficient RAM,) but it would take a smart coder who knows more than just how to re-jigger the source code into compiling for the 68K - you're not going to get acceptable performance running a renderer written for chunky bitmaps on planar hardware.

[commodorejohn]

There's also Duke3d for the megadrive. It's more of an homage than a port, but it's still pretty impressive considering the hardware.

And it's also approximately equivalent to Wolfenstein 3D, tech-wise. (Don't know if it uses the vertical-mirroring trick discussed in that Bloodshot interview, though.)

[commodorejohn]

Eh, mode X isn't planar so much as a strange hack to use the planar memory mapping hardware in chunky mode (the advantage being that it gives you access to all the video RAM, which you don't get from the BIOS-supplied linear-framebuffer chunky mode.) Actual VGA planar modes are the 16-color high-res modes and the EGA-compatibility modes.

[commodorejohn]

The documentation I provided that showed exactly what mode x was and why it was so fast. It is a planar mode, it is much faster, and it was present in even the earliest vga systems. You could call it a hack, but it was used so extensively in games, and programming books; it was a very well known, well documented, well used hack.

Well, I don't mean to imply anything negative when I call it a "hack" - it's definitely a useful mode, if a bit difficult to wrap your head around at first. I just mean that it's not a planar mode in the usual sense, where the bits of a pixel are spread across multiple linear bitmaps - each pixel is contained in one byte, it's just that the bytes for consecutive pixels are strangely interleaved by the VGA's normal planar hardware.
 

I never tire of reading this book:
http://www.drdobbs.com/high-performance-computing/184404919;jsessionid=14VZ5MDXC5NHRQE1GHPSKH4ATMY32JVN

Yes. Michael Abrash is a terrific writer, and his stuff is well worth the read even if you're never going to touch 80x86 programming or low-level EGA/VGA programming. His stuff did more to help me understand code optimization than anything else I'd read on the subject.

[commodorejohn]

In fact, it might even be the case that it would take less logic to implement a chunky HAM system than a planar one.

Given that HAM is by necessity fixed at a certain bit-depth, there's certainly no advantage to its being planar (besides the relevant one for OCS, that it allows reuse of the existing planar hardware.)