3D Realms has released the first dev blog on the upcoming old-school first-person shooter Ion Maiden. While not describing the process of designing the game itself, it is meant to showcase how games made in the venerable Build engine work. It is a 2.5D engine instead of pure 3D, so this article demystifies some bits of "smoke and mirrors" that create the illusion of a three-dimensional space. Here is an excerpt:
When approaching 3D in Build, you could split it in to following parts:
Sectors - Create rooms, stairs, balconies for enemies etc... could even be sofas, tables or cars! With sloping you can do much more believable objects than many engines of the time.
Sprites - No longer just player facing objects but also as wall or floor aligned flat objects. By combining these you can create rudimentary 3D shapes with with few unfortunate drawbacks. You can combine these with sectors to enhance the visuals.
Shading is very flexible and any floor/wall/slope/sprite can be individually shaded or palette swapped to create numerous variations and make objects really pop out.
Voxels (Volumetric pixels) Available only on later versions, these are essentially 3D sprites.
So what makes Build so special ? The biggest "3D" was that finally you could do overlapping sectors, which resulted in intersecting paths and overlapping areas referred to as SOS (Sector Over Sector). Still, there was one severe limitation: These sectors could never see each other at the same time! This did still allow vertical branching paths for the first time, you could submerge underwater, have sprite based platforms that could form solid looking floating objects that the player could jump on, air ducts, and staircases.
So if you're interested in behind-the-scenes info, love games like Duke Nukem 3D, Blood, and the original Shadow Warrior, and/or are just that hyped for Ion Maiden itself, you can read the whole article right here.