Game Engine Black Book DOOM available for download

[drfrag]

It's a very interesting read on the Doom engine. Seems something has gone wrong with Google Play and the pdf now it's available for free.
I encourage you to donate some amount and support the author, if i could i'd certainly do but i'm a very poor man unfortunately.
http://fabiensanglard.net/gebbdoom/

[drfrag]

And by reading the book now i know why low detail mode was that fast in DOS, it was still a bit faster than high in ZDoom tough.

With direct access to the VGA banks, "low detail mode" is a completely free optimization without the need to write the same pixel column twice, since the VGA mask is set up to write the same pixel to two banks simultaneously.

[Rachael]

There's that, but there's also the fact that it only has to process 160 columns instead of 320. In the software renderer, performance is lost in each vertical line. Widescreen would literally be Doom's curse, were it not for the fact that computers got dramatically faster in the time before widescreen actually became popular. Of course, this mostly applied to walls, and not floors.

[Graf Zahl]

There's that, but there's also the fact that it only has to process 160 columns instead of 320.

If it wasn't for that, low detail mode would make no sense. The tidbit that may be interesting here is that this actually reduced the hardware writes by half as well, not just the software processing.

[Rachael]

True, I wasn't saying that isn't important, I was merely saying there was more to it.

[drfrag]

Of course, also above the paragraph i quoted earlier:

In low resolution mode the engine only renders one out of very two columns but it writes them to the framebuffer twice. Given how the 3D renderer dominates runtime, this resulted in a tremendous performance improvement since fewer pixel values are generated but they also don’t have to transit the bus.

In ZDoom low detail was faster anyway specially without sound on very slow machines but i don't remember how much.
I might add a 3x1 mode BTW.