In 1998, Looking Glass Studios released the stealth game Thief: The Dark Project. The game utilized a purely software-rendered engine due to the limitations of hardware at the time. Sean Barrett, the primary author of the core rendering technology, recently discussed the technical details behind the game's visuals. The engine's design was inspired by Quake, but with unique approaches to visibility and overdraw.

Before Thief, Looking Glass games used grid-based worlds. The new engine, however, employed a portal-and-cell system for visibility, inspired by Seth Teller's PhD work. This method allowed for free-form level design. The system divided open areas into convex polyhedra known as cells, with portals marking adjacency. The engine conducted a breadth-first traversal to determine what needed rendering.

To manage overdraw, Thief used polygon clipping and back-to-front drawing. This helped minimize unnecessary pixel calculations. The article details how the use of bounding octagons further optimized visibility calculations. The techniques used were never formally documented until now. This provides a fascinating look at the ingenuity needed to create immersive 3D worlds before the widespread adoption of hardware acceleration.

The insights from Barrett offer a valuable glimpse into the development challenges of the late 90s. The game's engine was later adapted for System Shock 2 and Thief 2. Understanding these software rendering techniques provides context for the evolution of graphics technology. It also shows the importance of efficient rendering methods before powerful GPUs were commonplace.