The author dives into a detailed explanation of Quake’s visibility system, focusing on base visibility and portal culling to reduce overdraw in 3D games. The article delves into the concept of portals and potentially visible sets (PVS), discussing how Quake’s map tooling connects leaves with portals. The author also provides insight into the Quake map tool vis, which precomputes a leaf-to-leaf visibility matrix in three steps. Surprisingly, the article reveals that portals are arranged as a cell-and-portal graph, each having a directed edge and a normal vector for visibility determination. The main data structures of vis.py, including the Portal and Leaf classes, are explained in code.
https://30fps.net/pages/pvs-portals-and-quake/