It therefore focuses on those parts of the format necessary to perform map decompilation (conversion of the BSP file back into a VMF file which can be loaded by the Hammer map editor). This document is an extension of notes made by Rof during the writing of their Half-Life 2 BSP file decompiler, VMEX. Because of this, Max McGuire's article, Quake 2 BSP File Format is also of invaluable help in understanding the overall structure of the format and the parts of it that have remained the same or similar to its predecessors. The format is similar but not identical to the BSP file formats of the Half-Life 1 engine (GoldSrc), which is in turn based on the Quake, Quake II and QuakeWorld file formats, plus that of the later Quake III Arena. This document describes the structure of the BSP file format used by the Source engine.
