Ru/BSP (Source)

Эта статья основана на статье пользователя Rof "The Source Engine BSP File Format" от Октября 2005, взятой с сервиса Geocities перед тем как он был закрыт. Зеркало на оригинальную статью можно найти тут.
== Введение ==
Этот документ описывает структуру файлового формата используемого движком Source. Формат схож, но не идентичен фаловым форматам BSP используемых движком , которые в свою очередь основыны на файловых форматах используемых в , и QuakeWorld, плюс к этому и в поздних версиях . Поэтому статья пользователя Max McGuire, Quake 2 BSP File Format также является бесценной помощью в понимании общей структуры данного формата и его отдельных частей, которые остались в прежнем виде или схожи с их предшественниками.
Данный документ является расширением записок сделаных пользователем Rof во время написания своего декомпилятора файлов BSP для Half-Life 2, под названием . Поэтому основное внимание в этих записках уделяется тем частям формата, которые необходимы для (процесс преобразования BSP файла обратно в файл, который может быть загружен в редактор карт Hammer).
Большая часть информации, которая содержится в данном документе, происходит из статьи пользователя Max McGuire (о которой упоминалось выше), из исходного кода включенного в Source SDK (в частности заголовочный файл C public/bspfile.h), и из собственных эксперементов пользователя Rof в то время как он писал свой декомпилятор карт, VMEX.
Со стороны читателя предпологается некоторое знакомство с языками программирования C/C++, геометрией, и терминами Source маппинга. Исходный код (в большинтсве своем структуры C), который приводится в данном документе, написан моноширным шрифтом. Иногда, в угоду ясности и последовательности, структуры приводятся в виде, отличном от их фактических определений содержащихся в заголовочнх файлах SDK.
== Беглый обзор ==
В файле формата BSP содержится подавляющее большинство информации, которая необходима движку Source для рендеринга и проигрывания карты. Эта информация включает в себя геометрию всех полигонов на уровне; ссылки на имена и ориентации текстур, которые нужно нанести на полигоны; данные используемые для симуляции физического поведения игрока и других объектов во время игры; расположение и свойства всех сущностей (объектов) на карте, таких как brush-based, model (prop) based и невидимые (логические) сущности; BSP дерево и таблицу видимости используемые для определения расположения игрока в контексте геометрии карты и для рендеринга видимой части карты настолько эффективно, насколько это возможно. Файлы карты также могут содержать в себе любые другие кастомные текстуры и модели использованные на уровне, встроенные внутри Pakfile lump карты (смотреть ниже).
Информация хранящаяся не в BSP файле, включает в себя описание карты отображаемое в многопользовательских играх (таких как или ) после загрузки карты (хранится в файле под названием mapname.txt) и файл навигации ИИ используемый неигровыми персонажами (NPC), которым необходимо перемещаться по карте (хранится в файле mapname.nav). Благодаря тому как работает файловая система движка Source, эти внешние файлы также могут быть встроены в Pakfile lump BSP файла, однако зачастую это не используется.
Файлы оффициальных карт хранятся в формате, и доступны игровому движку через файловую систему Steam. Они могут быть извлечены из GCF файла для рассмотрения вне Steam с помощью утилиты, написаной пользователем Nemesis, . В более новых играх, в которых используется формат файлов , файлы карт зачастую хранятся прямо в файловой системе операционной системы.
Данные внутри BSP файлов могут хранится как в little-endian ("остроконечный") формате для PC/Mac, так и в big-endian ("тупоконечный") для PS3/X360. Смена порядка байтов (Byte-swapping) требуется когда загрузка little-endian файла выполняется на big-endian платформе, таких как Java и наоборот.
== Заголовок BSP файла ==
Файл BSP начинатся с заголовка. Это структура содержащая несколько полей, сначала идет поле, которое идентифицирует файл как Valve Source Engine BSP файл, далее поле определяющее версию формата, затем следует поле содержащее информацию о списке директорий местоположения файла, длину и версию всех подсекций файла (в количестве 64-x штук), известных как lumps, в которых хранятся разные части данных карты. Наконец, в последнем поле структуры содержится информация о ревизии карты.
Структура заголовка приведена в заголовочном файле public/bspfile.h, который входит в состав SDK, ссылки на этот файл будут широко использоваться на протяжении всего документа. В общем длина заголовка составляет 1036 байт:
 В Alien Swarm, эта структура была переименована в BSPHeader_t.
struct dheader_t
{
	int	ident; // BSP file identifier
	int	version; // BSP file version
	lump_t	lumps[HEADER_LUMPS]; // lump directory array
	int	mapRevision; // the map's revision (iteration, version) number
};
Где ident это 4-байтовое магическое число определенное как:
// little-endian "VBSP" 0x50534256
#define IDBSPHEADER	(('P'<<24)+('S'<<16)+('B'<<8)+'V')
Таким образом первые 4 байта файла BSP это всегда VBSP (в ASCII коде). Эти байты идентифицируют файл как BSP файл; другие форматы файлов BSP используют другие магические числа (так, например, в играх на движке Quake от id Software, файлы BSP начинаются с числа IBSP). BSP формат используемый движком и вовсе не использовал какие либо магические числа. Порядок в котором записано это магическое число также может быть использован для опрделения порядка следования байтов (endianness) в файле: VBSP используется для little-endian и PSBV для big-endian.
Второй integer (4-х байтовое число) это версия файлового формата BSP (BSPVERSION); для игр на движке Source, число находится в диапозоне от 19 до 21, за исключением VTMB (Vampire: The Masquerade – Bloodlines), которая использует более раннюю версию формата, 17 (смотреть таблицу ниже). Стоит отметить, что в файловых форматах BSP для других движков (HL1, Quake series, и т.д.) используются совершенно разные диапозоны номеров версий.
=== Версии ===
В этой таблице содержится информация о различных версиях BSP формата используемых в некоторых играх основаных на движке Source.
Версия	Игра 	Примечание
17 	Vampire: The Masquerade – Bloodlines	изменения: dface_t
17-18 	 	утекшая бета
19 	 	
19-20 	 	19 на момент релиза, частично 20 с момента обновления Source 2007/2009
19-20 	 	19 на момент релиза, частично 20 с момента обновления Source 2007/2009
19-20 	 	19 на момент релиза, частично 20 с момента обновления Source 2007/2009
19-20 	 	19 на момент релиза, частично 20 с момента обновления Source 2007/2009
20 	 	
20 	 	
20 	 	
20 	 	
20 	 	изменения ( newly compiled maps ): StaticPropLump_t ( version = 10 ), LZMA compressed game lumps, entity info and PAK files
20 	 	
20 	 	изменения: StaticPropLump_t ( version = 8 ) and dworldlight_t
20 	 	изменения: StaticPropLump_t ( version = 7 )
20 	 	изменения: dheader_t, StaticPropLump_t, texinfo_t, dgamelump_t, dmodel_t
20 	Vindictus 	many modified structs
20 	 	изменения: StaticPropLump_t
20 	 	изменения: StaticPropLump_t
21 	 	изменения: lump_t, old dbrushside_t
21 	 	
21 	 	изменения: StaticPropLump_t ( version = 9 ), dbrushside_t and other structs
21 	 	изменения: StaticPropLump_t ( version = 10 )
21 	(коммерческий релиз) 	изменения: StaticPropLump_t
21 	(коммерческий релиз) 	
21 	 	256-bit XOR encryption
22 	 	ранние бета версии, изменения: dbrushside_t, ddispinfo_t
23 	 	изменения: dbrushside_t, ddispinfo_t, doverlay_t
27 	 	
29 	 	сильно изменен
За большим количеством деталей относящимся к специфичным, для конкретных игр, форматам BSP, обращаться к .
=== Структура Lump ===
Затем следует массив из 16-байтных структур lump_t. Константа HEADER_LUMPS определена как 64, поэтому массив состоит из 64-х элементов. Однока, в зависимости от игры и версии формата, некоторые lump'ы могут быть не определены или пусты.
Cтруктура lump_t определена в заголовочном файле файле bspfile.h: 
struct lump_t
{
	int	fileofs;	// offset into file (bytes)
	int	filelen;	// length of lump (bytes)
	int	version;	// lump format version
	char	fourCC[4];	// lump ident code
};
Первые два integer'а содержат отступ в байтах (от начала BSP файла) и длину в байтах, которую имеет блок данных lump'а; далее integer определяющий номер версии формата данного lump'а (обычно нуль), и затем четырех байтовый идентификатор (массив из 4-х char, каждый из которых занимает 1 байт), который обычно равен { 0, 0, 0, 0 }. Для сжатых lump'ов, fourCC (последнее поле) содержит несжатый размер данных lump'а в форме integer'а form (детали смотреть в секции Сжатие Lump'ов ). У неиспользуемых членов массива lump_t (у которых нет даннх на которые бы они ссылались) все элементы (поля) установлены в нуль.
Сдвиги lump'ов (и им соответствующие данные) всегда округляются до ближайшей 4-байтовой границы, хотя lump и вовсе может не иметь длины.
=== Типы Lump ===
Тип данных, на которые указывает массив lump_t определяется его положением в массиве; например, первый lump в массиве (Lump 0) это всегда данные сущностей (entity) BSP файла (смотреть ниже). Фактическое местонахождение данных в BSP файле определяется сдвигом и длиной записи этого lump'а, и они не находятся в какои-либо кокретном порядке; например, данные сущности (entity data) обычно хранятся по направлению к концу BSP файла несмотря на то, что являются первыми в lump массиве. Таким образом, массив заголовков lump_t это директория где фактически находятся lump данные, которые могут быть расположены где-нибудь в другом месте внутри файла.
Порядок в lump массиве определен следующим образом:
Индекс	Движок	Имя 	Назначение
0 	 	LUMP_ENTITIES 	Энтити карты
1 	 	LUMP_PLANES 	Массив плоскостей
2 	 	LUMP_TEXDATA 	Указатели на имена текстур
3 	 	LUMP_VERTEXES 	Массив вершин
4 	 	LUMP_VISIBILITY 	Массив битов со сжатой видимостью
5 	 	LUMP_NODES 	Узлы дерева BSP
6 	 	LUMP_TEXINFO 	Массив текстур на поверхностях
7 	 	LUMP_FACES 	Массив на поверхностях
8 	 	LUMP_LIGHTING 	Образцы карты освещённости
9 	 	LUMP_OCCLUSION 	Перегороженные полигоны и вершины
10 	 	LUMP_LEAFS 	Узлы-листья BSP дерева
11 	 	LUMP_FACEIDS 	Корреляция между d-поверхностями и ID-поверхностями Хаммера. Также используется как случайный источник для размещения .
12 	 	LUMP_EDGES 	Массив граней
13 	 	LUMP_SURFEDGES 	Индекс граней
14 	 	LUMP_MODELS 	Брашевые модели (геометрия брашевых энтить)
15 	 	LUMP_WORLDLIGHTS 	Внутреннее освещение карты, преобразованное в lump-энтитю
16 	 	LUMP_LEAFFACES 	Индекс граней в каждом листе
17 	 	LUMP_LEAFBRUSHES 	Индекс брашей в каждом листе
18 	 	LUMP_BRUSHES 	Массив брашей
19 	 	LUMP_BRUSHSIDES 	Brushside массив
20 	 	LUMP_AREAS 	Area массив
21 	 	LUMP_AREAPORTALS 	Порталы между зонами
22 	 	LUMP_PORTALS 	
22 	 	LUMP_UNUSED0 	Не используется
22 	 	LUMP_PROPCOLLISION 	Список статичных выпуклых пропов
23 	 	LUMP_CLUSTERS 	Leaves that are enterable by the player
23 	 	LUMP_UNUSED1 	Не используется
23 	 	LUMP_PROPHULLS 	Static prop convex hulls
24 	 	LUMP_PORTALVERTS 	Vertices of portal polygons
24 	 	LUMP_UNUSED2 	Unused
24 	 	LUMP_PROPHULLVERTS 	Static prop collision vertices
25 	 	LUMP_CLUSTERPORTALS 	
25 	 	LUMP_UNUSED3 	Unused
25 	 	LUMP_PROPTRIS 	Static prop per hull triangle index start/count
26 	 	LUMP_DISPINFO 	Displacement surface array
27 	 	LUMP_ORIGINALFACES 	Brush faces array before splitting
28 	 	LUMP_PHYSDISP 	Displacement physics collision data
29 	 	LUMP_PHYSCOLLIDE 	Physics collision data
30 	 	LUMP_VERTNORMALS 	Face plane normals
31 	 	LUMP_VERTNORMALINDICES 	Face plane normal index array
32 	 	LUMP_DISP_LIGHTMAP_ALPHAS 	Displacement lightmap alphas (unused/empty since Source 2006)
33 	 	LUMP_DISP_VERTS 	Vertices of displacement surface meshes
34 	 	LUMP_DISP_LIGHTMAP_SAMPLE_POSITIONS	Displacement lightmap sample positions
35 	 	LUMP_GAME_LUMP 	Game-specific data lump
36 	 	LUMP_LEAFWATERDATA 	Data for leaf nodes that are inside water
37 	 	LUMP_PRIMITIVES 	Water polygon data
38 	 	LUMP_PRIMVERTS 	Water polygon vertices
39 	 	LUMP_PRIMINDICES 	Water polygon vertex index array
40 	 	LUMP_PAKFILE 	Embedded uncompressed Zip-format file
41 	 	LUMP_CLIPPORTALVERTS 	Clipped portal polygon vertices
42 	 	LUMP_CUBEMAPS 	env_cubemap location array
43 	 	LUMP_TEXDATA_STRING_DATA 	Texture name data
44 	 	LUMP_TEXDATA_STRING_TABLE 	Index array into texdata string data
45 	 	LUMP_OVERLAYS 	info_overlay data array
46 	 	LUMP_LEAFMINDISTTOWATER 	Distance from leaves to water
47 	 	LUMP_FACE_MACRO_TEXTURE_INFO 	Macro texture info for faces
48 	 	LUMP_DISP_TRIS 	Displacement surface triangles
49 	 	LUMP_PHYSCOLLIDESURFACE 	Compressed win32-specific Havok terrain surface collision data. Deprecated and no longer used.
49 	 	LUMP_PROP_BLOB 	Static prop triangle and string data
50 	 	LUMP_WATEROVERLAYS 	
51 	 	LUMP_LIGHTMAPPAGES 	Alternate lightdata implementation for Xbox
51 	 	LUMP_LEAF_AMBIENT_INDEX_HDR 	Index of LUMP_LEAF_AMBIENT_LIGHTING_HDR
52 	 	LUMP_LIGHTMAPPAGEINFOS 	Alternate lightdata indices for Xbox
52 	 	LUMP_LEAF_AMBIENT_INDEX 	Index of LUMP_LEAF_AMBIENT_LIGHTING
53 	 	LUMP_LIGHTING_HDR 	HDR lightmap samples
54 	 	LUMP_WORLDLIGHTS_HDR 	Internal HDR world lights converted from the entity lump
55 	 	LUMP_LEAF_AMBIENT_LIGHTING_HDR 	
56 	 	LUMP_LEAF_AMBIENT_LIGHTING 	
57 	 	LUMP_XZIPPAKFILE 	XZip version of pak file for Xbox. Deprecated.
58 	 	LUMP_FACES_HDR 	HDR maps may have different face data
59 	 	LUMP_MAP_FLAGS 	Extended level-wide flags. Not present in all levels.
60 	 	LUMP_OVERLAY_FADES 	Fade distances for overlays
61 	 	LUMP_OVERLAY_SYSTEM_LEVELS 	System level settings (min/max CPU & GPU to render this overlay)
62 	 	LUMP_PHYSLEVEL 	
63 	 	LUMP_DISP_MULTIBLEND 	Displacement multiblend info
Имейте в виду, что lump-ы 53-56 используются только в BSP файлах версии 20 и выше. Но lump-ы 22-25 не используются в BSP файлах версии 20.
Структура lump для известных записей описанна ниже. Большинство lump - это обычные массивы структур; Однако, длины переменных зависят от их содержания. Максимальные размеры записей в каждом lump также обозначено в заголовке 'bspfile.h' как MAX_MAP*.
( Ссылка на заголовок bspfile.h - https://github.com/ValveSoftware/source-sdk-2013/blob/master/mp/src/public/bspfile.h#L56 )
И наконец, заголовки заканчиваются цельным числом (не десятичным) содержащее число ревизии карты. Это число основано на ревизии числа *.vmf файла карты (mapversion), который увеличивает каждый раз, когда карта сохраняется в Hammer editor.
Сразу после заголовка идут первые структуры lump-а. Это может быть любой lump в предшествующем листе (для использование после смещения этого lump-а),
хотя в практике первые структуры lump - являются Lump-1, который хранит массив данных плоскости
=== Сжатый lump ===
BSP файлы для консольных платформ (таких как PlayStation 3 и Xbox 360) обычно имеют свои lump с LZMA. В таком случае, структура lump начинается со следующего заголовка ('public/tier1/lzmaDecoder.h'):
(Ссылка на заголовок lzmaDecoder.h - https://github.com/ValveSoftware/source-sdk-2013/blob/master/sp/src/public/tier1/lzmaDecoder.h#L19 )
struct lzma_header_t
{
	unsigned int	id;
	unsigned int	actualSize;		// всегда с прямым порядком байтов
	unsigned int	lzmaSize;		// всегда с прямым порядком байтов
	unsigned char	properties[5];
};
Где id обозначается как:
// little-endian "LZMA"
#define LZMA_ID	(('A'<<24)|('M'<<16)|('Z'<<8)|('L'))
Есть два специальных события для сжатия lump-ов: LUMP_PAKFILE никогда не сжимается и каждый игровой lump в LUMP_GAME_LUMP сжимается индивидуально. Размер сжатия игрового lump-а может быть определён вычитанием текущих игрового lump-го смещения с этим следующим записем.
Именно по этой причине последний игровой lump является пустым, который хранит в себе только запись.
== Lump'ы ==
=== Плоскости ===
Основа геометрии BSP определена плоскостями. которые используются для связывания поверхностей через структуры BSP файла
Lump плоскостей (Lump 1) определён в структуре dplane_t:
struct dplane_t
{
	Vector	normal;	// Обозначает вектор нормали(т.е. единичный отрезок, перпендикулярный самой плоскости)
	float	dist;	// расстояние от центра до ближайшей точки плоскости 
	int	type;	// вспомогательная переменная, используемая для уточнения направления плоскости(т.е. либо плоскость обращена в оси X, либо Y и т.д). Подробнее об этой переменной говориться ниже.
};
Где: - трёхмерный вектор, имеет вид:
struct Vector
{
	float x;
	float y;
	float z;
};
Тип float, как и тип int(в данном случае _int32), имеет размер в 4 байта, поэтому размер структуры составляет 20 байт. Вы можете получить количество плоскостей, разделив размер этого lump'а на размер этой структуры, то есть: 
 int num_planes = Lump[1].filelen/sizeof(dplane_t); 
Плоскость объявляется переменной normal, вектор нормали(единичный вектор, перпендикулярный к плоскости). Также расположение плоскости в пространстве задаётся переменной dist, которая определяет расстояние от центра координат (0,0,0) до ближайшей точки плоскости. 
Плоскость определяется точками (x, y, z), которые удовлетворяют равенству:
Ax + By + Cz = D
Где: A, B, и C - координаты вектора нормали normal.x, normal.y and normal.z соответственно. 
 D - dist(переменная была описана выше).
Каждая плоскость бесконечна и делит всё пространство(игровую карту) на 3 части: На плоскости (F=0) (в данном случае получается двумерное пространство), впереди плоскости(F>0), и позади плоскости (F<0).
Но имейте в виду, плоскости имеют частичную ориентацию в пространстве. Ориентации плоскости может быть перевернута, если одно из значений компонентов A, B, C, и D будет отрицательным(вектор нормали или расстояние может иметь отрицательные значения).
Переменная type указывает, к какой оси она перпендикулярна. Имеет значение в диапазоне [0;5]. Если эта переменная имеет значения 0, 1 или 2, то она обращена(перпендикулярна) оси X, Y или Z соответственно. Другие значения (3,4,5) указывают, что она не перпендикулярна никакой оси и указывать к какой оси нормаль этой плоскости ближе. Обычно это переменная не используется.
На карте может быть до 65536 плоскостей (MAX_MAP_PLANES)
=== Вершины ===
Lump вершины (Lump 3) - массив из координат вершин всей геометрии карты(указывает вершины не только объектов, брашей, но и границы карты). Координата вершины- трёхмерный вектор, состоящий из трёх переменных типа float:
struct Vertex
{
	float x;
	float y;
	float z;
};
Тип float имеет размер 4 байт. Значит структура имеет размерность 3*4=12 байт.
Чтобы получить количество вершин на карте, нужно разделить размер lump'а вершин на размер структуры вершин:
 int num_verts = Lump[3].filelen/sizeof(Vertex); 
Стоит учесть, что, если вершина находится между гранями, она может повторяться в массиве вершин, так как лежит в разных плоскостях.
Также, в целях оптимизации карт, компилятор может добавить дополнительные вершины для разбиения граней. То есть, если была одна грань, состоящая из одного прямоугольника, то в целях оптимизации эта грань может содержать в себе 2-4 прямоугольников.
На карте может быть до 65536 вершин (MAX_MAP_VERTS).
=== Рёбра ===
Lump рёбер (Lump 12) - массив структуры dedge_t:
struct dedge_t
{
	unsigned short	v[2];	// индекс на массив вершин
};
unsigned short имеет размер 2 байта. Значит, чтобы получить количество рёбер на карте, нужно размер lump'а рёбер поделить на размер структуры рёбер:
int num_edges = Lump[12].filelen/sizeof(dedge_t);
Каждое ребро просто связывает две вершины, индекс которых определён в переменной v. Ребро прямую при помощи двух вершин. Индекс рёбер упоминается в массиве Surfedge(Смотрите ниже).
На карте может быть до 256000 рёбер (MAX_MAP_EDGES).
=== Surfedge ===
The Surfedge lump (Lump 13), presumable short for surface edge, is an array of (signed) integers. Surfedges are used to reference the edge array, in a somewhat complex way. The value in the surfedge array can be positive or negative. The absolute value of this number is an index into the edge array: if positive, it means the edge is defined from the first to the second vertex; if negative, from the second to the first vertex.
By this method, the Surfedge array allows edges to be referenced for a particular direction. (See the face lump entry below for more on why this is done).
There is a limit of 512000 (MAX_MAP_SURFEDGES) surfedges per map. Note that the number of surfedges is not necessarily the same as the number of edges in the map.
=== Face and original face ===
The face lump (Lump 7) contains the major geometry of the map, used by the game engine to render the viewpoint of the player. The face lump contains faces after they have undergone the BSP splitting process; they therefore do not directly correspond to the faces of brushes created in Hammer. Faces are always flat, convex polygons, though they can contain edges that are co-linear.
The face lump is one of the more complex structures of the map file. It is an array of dface_t entries, each 56 bytes long:
struct dface_t
{
	unsigned short	planenum;		// the plane number
	byte		side;			// faces opposite to the node's plane direction
	byte		onNode;			// 1 of on node, 0 if in leaf
	int		firstedge;		// index into surfedges
	short		numedges;		// number of surfedges
	short		texinfo;		// texture info
	short		dispinfo;		// displacement info
	short		surfaceFogVolumeID;	// ?
	byte		styles[4];		// switchable lighting info
	int		lightofs;		// offset into lightmap lump
	float		area;			// face area in units^2
	int		LightmapTextureMinsInLuxels[2];	// texture lighting info
	int		LightmapTextureSizeInLuxels[2];	// texture lighting info
	int		origFace;		// original face this was split from
	unsigned short	numPrims;		// primitives
	unsigned short	firstPrimID;
	unsigned int	smoothingGroups;	// lightmap smoothing group
};
The first member planenum is the plane number, i.e., the index into the plane array that corresponds to the plane that is aligned with this face in the world. Side is zero if this plane faces in the same direction as the face (i.e. "out" of the face) or non-zero otherwise.
Firstedge is an index into the Surfedge array; this and the following numedges entries in the surfedge array define the edges of the face. As mentioned above, whether the value in the surfedge array is positive or negative indicates whether the corresponding pair of vertices listed in the Edge array should be traced from the first vertex to the second, or vice versa. The vertices which make up the face are thus referenced in clockwise order; when looking towards the face, each edge is traced in a clockwise direction. This makes rendering the faces easier, and allows quick culling of faces that face away from the viewpoint.
Texinfo is an index into the Texinfo array (see below), and represents the texture to be drawn on the face. Dispinfo is an index into the Dispinfo array is the face is a displacement surface (in which case, the face defines the boundaries of the surface); otherwise, it is -1. SurfaceFogVolumeID appears to be related to drawing fogging when the player's viewpoint is underwater or looking through water.
OrigFace is the index of the original face which was split to produce this face. NumPrims and firstPrimID are related to the drawing of "Non-polygonal primitives" (see below). The other members of the structure are used to reference face-lighting info (see the Lighting lump, below).
The face array is limited to 65536 (MAX_MAP_FACES) entries.
The original face lump (Lump 27) has the same structure as the face lump, but contains the array of faces before the BSP splitting process is done. These faces are therefore closer to the original brush faces present in the precompile map than the face array, and there are less of them. The origFace entry for all original faces is zero. The maximum size of the original face array is also 65536 entries.
Both the face and original face arrays are culled; that is, many faces present before compilation of the map (primarily those that face towards the "void" outside the map) are removed from the array.
=== Браши и брашсайды ===
Lump браша (Lump 18) содержит все исходные браши, когда они ещё не подверглись компиляции. В отличие от граней, браши constructive solid geometry (CSG) определяются плоскостями, а не вершинами и рёбрами. Это и является главным преимуществом брашей и брашсайдов, ведь при помощи них можно легко декомпилировать карту в исходный файл для дальнейших изменений.
Lump структуры брашей имеет размер 12 байт dbrush_t:
struct dbrush_t
{
	int	firstside;	// индекс первой стороны
	int	numsides;	// количество сторон в браши
	int	contents;	// флаги
};
The first integer firstside is an index into the brushside array lump, this and the following numsides brushsides make up all the sides in this brush. The contents entry contains bitflags which determine the contents of this brush. The values are binary-ORed together, and are defined in the public/bspflags.h file:
Name 	Value 	Notes
CONTENTS_EMPTY 	0 	No contents
CONTENTS_SOLID 	0x1 	an eye is never valid in a solid
CONTENTS_WINDOW 	0x2 	translucent, but not watery (glass)
CONTENTS_AUX 	0x4 	
CONTENTS_GRATE 	0x8 	alpha-tested "grate" textures. Bullets/sight pass through, but solids don't
CONTENTS_SLIME 	0x10 	
CONTENTS_WATER 	0x20 	
CONTENTS_MIST 	0x40 	
CONTENTS_OPAQUE 	0x80 	block AI line of sight
CONTENTS_TESTFOGVOLUME 	0x100 	things that cannot be seen through (may be non-solid though)
CONTENTS_UNUSED 	0x200 	unused
CONTENTS_UNUSED6 	0x400 	unused
CONTENTS_TEAM1 	0x800 	per team contents used to differentiate collisions between players and objects on different teams
CONTENTS_TEAM2 	0x1000 	per team contents used to differentiate collisions between players and objects on different teams
CONTENTS_IGNORE_NODRAW_OPAQUE	0x2000 	ignore CONTENTS_OPAQUE on surfaces that have SURF_NODRAW
CONTENTS_MOVEABLE 	0x4000 	hits entities which are MOVETYPE_PUSH (doors, plats, etc.)
CONTENTS_AREAPORTAL 	0x8000 	remaining contents are non-visible, and don't eat brushes
CONTENTS_PLAYERCLIP 	0x10000 	
CONTENTS_MONSTERCLIP 	0x20000 	
CONTENTS_CURRENT_0 	0x40000 	currents can be added to any other contents, and may be mixed
CONTENTS_CURRENT_90 	0x80000 	currents can be added to any other contents, and may be mixed
CONTENTS_CURRENT_180 	0x100000 	currents can be added to any other contents, and may be mixed
CONTENTS_CURRENT_270 	0x200000 	currents can be added to any other contents, and may be mixed
CONTENTS_CURRENT_UP 	0x400000 	currents can be added to any other contents, and may be mixed
CONTENTS_CURRENT_DOWN 	0x800000 	currents can be added to any other contents, and may be mixed
CONTENTS_ORIGIN 	0x1000000 	removed before bsping an entity
CONTENTS_MONSTER 	0x2000000 	should never be on a brush, only in game
CONTENTS_DEBRIS 	0x4000000 	
CONTENTS_DETAIL 	0x8000000 	brushes to be added after vis leafs
CONTENTS_TRANSLUCENT 	0x10000000	auto set if any surface has trans
CONTENTS_LADDER 	0x20000000	
CONTENTS_HITBOX 	0x40000000	use accurate hitboxes on trace
Some of these flags seem to be inherited from previous game engines and are not used in Source maps. They are also used to describe to contents of the map's leaves (see below). The CONTENTS_DETAIL flag is used to mark brushes that were in entities before compiling.
The brush array is limited to 8192 entries (MAX_MAP_BRUSHES).
The brushside lump (Lump 19) is an array of 8-byte structures:
struct dbrushside_t
{
	unsigned short	planenum;	// facing out of the leaf
	short		texinfo;	// texture info
	short		dispinfo;	// displacement info
	short		bevel;		// is the side a bevel plane?
};
Planenum is an index info the plane array, giving the plane corresponding to this brushside. Texinfo and dispinfo are references into the texture and displacement info lumps. Bevel is zero for normal brush sides, but 1 if the side is a bevel plane (which seem to be used for collision detection).
Unlike the face array, brushsides are not culled (removed) where they touch the void. Void-facing sides do however have their texinfo entry changed to the tools/toolsnodraw texture during the compile process. Note there is no direct way of linking brushes and brushsides and the corresponding face array entries which are used to render that brush. Brushsides are used by the engine to calculate all player physics collision with world brushes. (Vphysics objects use lump 29 instead.)
The maximum number of brushsides is 65536 (MAX_MAP_BRUSHSIDES). The maximum number of brushsides on a single brush is 128 (MAX_BRUSH_SIDES).
=== Node and leaf ===
The node array (Lump 5) and leaf array (Lump 10) define the Binary Space Partition (BSP) tree structure of the map. The BSP tree is used by the engine to quickly determine the location of the player's viewpoint with respect to the map geometry, and along with the visibility information (see below), to decide which parts of the map are to be drawn.
The nodes and leaves form a tree structure. Each leaf represents a defined volume of the map, and each node represents the volume which is the sum of all its child nodes and leaves further down the tree.
Each node has exactly two children, which can be either another node or a leaf. A child node has two further children, and so on until all branches of the tree are terminated with leaves, which have no children. Each node also references a plane in the plane array. When determining the player's viewpoint, the engine is trying to find which leaf the viewpoint falls inside. It first compares the coordinates of the point with the plane referenced in the headnode (Node 0). If the point is in front of the plane, it then moves to the first child of the node; otherwise, it moves to the second child. If the child is a leaf, then it has completed its task. If it is another node, it then performs the same check against the plane referenced in this node, and follows the children as before. It therefore traverses the BSP tree until it finds which leaf the viewpoint lies in. The leaves, then, completely divide up the map volume into a set of non-overlapping, convex volumes defined by the planes of their parent nodes.
For more information on how the BSP tree is constructed, see the article "BSP for dummies".
The node array consists of 32-byte structures:
struct dnode_t
{
	int		planenum;	// index into plane array
	int		children[2];	// negative numbers are -(leafs + 1), not nodes
	short		mins[3];	// for frustum culling
	short		maxs[3];
	unsigned short	firstface;	// index into face array
	unsigned short	numfaces;	// counting both sides
	short		area;		// If all leaves below this node are in the same area, then
					// this is the area index. If not, this is -1.
	short		paddding;	// pad to 32 bytes length
};
Planenum is the entry in the plane array. The children[] members are the two children of this node; if positive, they are node indices; if negative, the value (-1-child) is the index into the leaf array (e.g., the value -100 would reference leaf 99).
The members mins[] and maxs[] are coordinates of a rough bounding box surrounding the contents of this node. The firstface and numfaces are indices into the face array that show which map faces are contained in this node, or zero if none are. The area value is the map area of this node (see below). There can be a maximum of 65536 nodes in a map (MAX_MAP_NODES).
The leaf array is an array with 56 bytes per element:
struct dleaf_t
{
	int			contents;		// OR of all brushes (not needed?)
	short			cluster;		// cluster this leaf is in
	short			area:9;			// area this leaf is in
	short			flags:7;		// flags
	short			mins[3];		// for frustum culling
	short			maxs[3];
	unsigned short		firstleafface;		// index into leaffaces
	unsigned short		numleaffaces;
	unsigned short		firstleafbrush;		// index into leafbrushes
	unsigned short		numleafbrushes;
	short			leafWaterDataID;	// -1 for not in water
	//!!! NOTE: for maps of version 19 or lower uncomment this block
	/*
	CompressedLightCube	ambientLighting;	// Precaculated light info for entities.
	short			padding;		// padding to 4-byte boundary
	*/
};
The leaf structure has similar contents to the node structure, except it has no children and no reference plane. Additional entries are the contents flags (see the brush lump, above), which shows the contents of any brushes in the leaf, and the cluster number of the leaf (see below). The area and flags members share a 16-bit bitfield and contain the area number and flags relating to the leaf. Firstleafface and numleaffaces index into the leafface array and show which faces are inside this leaf, if any. Firstleafbrush and numleafbrushes likewise index brushes inside this leaf through the leafbrush array.
The ambientLighting element is related to lighting of objects in the leaf, and consists of a CompressedLightCube structure, which is 24 bytes in length. Version 17 BSP files have a modified dleaf_t structure that omits the ambient lighting data, making the entry for each leaf only 32 bytes in length. The same shortened structure is also used for version 20 BSP files, with the ambient lighting information for LDR and HDR probably contained in the new lumps 55 and 56.
All leaves are convex polyhedra, and are defined by the planes of their parent nodes. They do not overlap. Any point in the coordinate space is in one and only one leaf of the map. A leaf which is not filled with a solid brush and can be entered by the player in the usual course of the game has a cluster number set; this is used in conjunction with the visibility information (below).
There are usually multiple, unconnected BSP trees in a map. Each one corresponds to an entry in model array (see below) and the headnode of each tree is referenced there. The first tree is the worldspawn model, the overall geometry of the level. Successive trees are the models of each brush entity in the map.
The creation of the BSP tree is done by the VBSP program, during the first phase of map compilation. Exactly how the tree is created, and how the map is divided into leaves, can be influenced by the map author by the use of HINT brushes, func_details, and the careful layout of all brushes in the map.
=== LeafFace and LeafBrush ===
The leafface lump (Lump 16) is an array of unsigned shorts which are used to map from faces referenced in the leaf structure to indices in the face array. The leafbrush lump (also an array of unsigned shorts)(Lump 17) does the same thing for brushes referenced in leaves. Their maximum sizes are both 65536 entries (MAX_MAP_LEAFFACES, MAX_MAP_LEAFBRUSHES).
=== Textures ===
The texture information in a map is split across a number of different lumps. The Texinfo lump is the most fundamental, referenced by the face and brushside arrays, and it in turn references the other texture lumps.
==== Texinfo ====
The texinfo lump (Lump 6) contains an array of texinfo_t structures:
struct texinfo_t
{
	float	textureVecs[2][4];	// [s/t][xyz offset]
	float	lightmapVecs[2][4];	// [s/t][xyz offset] - length is in units of texels/area
	int	flags;			// miptex flags	overrides
	int	texdata;		// Pointer to texture name, size, etc.
}
Each texinfo is 72 bytes long.
The first array of floats is in essence two vectors that represent how the texture is orientated and scaled when rendered on the world geometry. The two vectors, s and t, are the mapping of the left-to-right and down-to-up directions in the texture pixel coordinate space, onto the world. Each vector has an x, y, and z component, plus an offset which is the "shift" of the texture in that direction relative to the world. The length of the vectors represent the scaling of the texture in each direction.
The 2D coordinates () of a texture pixel (or ) are mapped to the world coordinates (x, y, z) of a point on a face by:
u = tv0,0 * x + tv0,1 * y + tv0,2 * z + tv0,3
v = tv1,0 * x + tv1,1 * y + tv1,2 * z + tv1,3
(ie. The dot product of the vectors with the vertex plus the offset in that direction. Where tvA,B is textureVecs[A][B].
Furthermore, after calculating (u, v), to convert them to texture coordinates which you would send to your graphics card, divide u and v by the width and height of the texture respectively.
The lightmapVecs float array performs a similar mapping of the lightmap samples of the texture onto the world.
The flags entry contains bitflags which are defined in bspflags.h:
Name 	Value 	Notes
SURF_LIGHT 	0x1 	value will hold the light strength
SURF_SKY2D 	0x2 	don't draw, indicates we should skylight + draw 2d sky but not draw the 3D skybox
SURF_SKY 	0x4 	don't draw, but add to skybox
SURF_WARP 	0x8 	turbulent water warp
SURF_TRANS 	0x10 	
SURF_NOPORTAL 	0x20 	the surface can not have a portal placed on it
SURF_TRIGGER 	0x40 	FIXME: This is an xbox hack to work around elimination of trigger surfaces, which breaks occluders
SURF_NODRAW 	0x80 	don't bother referencing the texture
SURF_HINT 	0x100 	make a primary bsp splitter
SURF_SKIP 	0x200 	completely ignore, allowing non-closed brushes
SURF_NOLIGHT 	0x400 	Don't calculate light
SURF_BUMPLIGHT	0x800 	calculate three lightmaps for the surface for bumpmapping
SURF_NOSHADOWS	0x1000	Don't receive shadows
SURF_NODECALS 	0x2000	Don't receive decals
SURF_NOCHOP 	0x4000	Don't subdivide patches on this surface
SURF_HITBOX 	0x8000	surface is part of a hitbox
The flags seem to be derived from the texture's .vmt file contents, and specify special properties of that texture.
==== Texdata ====
Finally the texdata entry is an index into the Texdata array, and specifies the actual texture.
The index of a Texinfo (referenced from a face or brushside) may be given as -1; this indicates that no texture information is associated with this face. This occurs on compiling brush faces given the SKIP, CLIP, or INVISIBLE type textures in the editor.
The texdata array (Lump 2) consists of the structures:
struct dtexdata_t
{
	Vector	reflectivity;		// RGB reflectivity
	int	nameStringTableID;	// index into TexdataStringTable
	int	width, height;		// source image
	int	view_width, view_height;
};
The reflectivity vector corresponds to the RGB components of the reflectivity of the texture, as derived from the material's .vtf file. This is probably used in radiosity (lighting) calculations of what light bounces from the texture's surface. The nameStringTableID is an index into the TexdataStringTable array (below). The other members relate to the texture's source image.
==== TexdataStringData and TexdataStringTable ====
The TexdataStringTable (Lump 44) is an array of integers which are offsets into the TexdataStringData (lump 43). The TexdataStringData lump consists of concatenated null-terminated strings giving the texture name.
There can be a maximum of 12288 texinfos in a map (MAX_MAP_TEXINFO). There is a limit of 2048 texdatas in the array (MAX_MAP_TEXDATA) and up to 256000 bytes in the TexdataStringData data block (MAX_MAP_TEXDATA_STRING_DATA). Texture name strings are limited to 128 characters (TEXTURE_NAME_LENGTH).
=== Model ===
A Model, in the terminology of the BSP file format, is a collection of brushes and faces, often called a "bmodel". It should not be confused with the prop models used in Hammer, which are usually called "studiomodels" in the SDK source.
The model lump (Lump 14) consists of an array of 24-byte dmodel_t structures:
struct dmodel_t
{
	Vector	mins, maxs;		// bounding box
	Vector	origin;			// for sounds or lights
	int	headnode;		// index into node array
	int	firstface, numfaces;	// index into face array
};
Mins and maxs are the bounding points of the model. Origin is the coordinates of the model in the world, if set. Headnode is the index of the top node in the node array of the BSP tree which describes this model. Firstface and numfaces index into the face array and give the faces which make up this model.
The first model in the array (Model 0) is always "worldspawn", the overall geometry of the whole map excluding entities (but including func_detail brushes). The subsequent models in the array are associated with brush entities, and referenced from the entity lump.
There is a limit of 1024 models in a map (MAX_MAP_MODELS), including the worldspawn model zero.
=== Visibility ===
The visibility lump (Lump 4) is in a somewhat different format to the previously mentioned lumps. To understand it, some discussion of how the Source engine's visibility system works in necessary.
As mentioned in the Node and leaf lumps section above, every point in the map falls into exactly one convex volume called a leaf. All leaves that are on the inside of the map (not touching the void), and that are not covered by a solid brush can potentially have the player's viewpoint inside it during normal gameplay. Each of these enterable leaves (also called ) gets assigned a cluster number. In Source BSP files, each enterable leaf corresponds to just one cluster.
(The terminology is slightly confusing here. According to the "Quake 2 BSP File Format" article, in the Q2 engine there could be multiple adjacent leaves in each cluster - thus the cluster is so called because it is a cluster of leaves. It seems from the SDK source that this situation may also occur during the compilation of Source maps; however, after the compile process is finished these adjacent leaves (and their parent nodes) are merged into a single leaf. In all finished Source maps that have been examined, it seems there is only ever one leaf per cluster. Therefore, in Source BSP files the distinction between clusters and enterable leaves (visleaves) is not meaningful.)
Each cluster, then, is a volume in the map that the player can potentially be in. To render the map quickly, the game engine draws the geometry of only those clusters which are visible from the current cluster. Clusters which are completely occluded from view from the player's cluster need not be drawn. Calculating cluster-to-cluster visibility is the responsibility of the VVIS compile tool, and the resulting data is stored in the Visibility lump.
Once the engine knows a cluster is visible, the leaf data references all faces present in that cluster, allowing the contents of the cluster to be rendered.
The data is stored as an array of bit-vectors; for each cluster, a list of which other clusters are visible from it are stored as individual bits (1 if visible, 0 if occluded) in an array, with the nth bit position corresponding to the nth cluster. This is known as the cluster's . Because of the large size of this data, the bit vectors are compressed by run-length encoding groups of zero bits in each vector.
There is also a array created for each cluster; this marks which clusters can hear sounds occurring in other clusters. The PAS seems to be created by merging the PVS bits of all clusters in current cluster's PVS.
The Visibilty lump is defined as:
struct dvis_t
{
	int	numclusters;
	int	byteofs[numclusters][2]
};
The first integer is the number of clusters in the map. It is followed by an array of integers giving the byte offset from the start of the lump to the start of the PVS bit array for each cluster, followed by the offset to the PAS array. Immediately following the array are the compressed bit vectors.
The decoding of the run-length compression works as follows: To find the PVS of a given cluster, start at the byte given by the offset in the byteofs[] array. If the current byte in the PVS buffer is zero, the following byte multiplied by 8 is the number of clusters to skip that are not visible. If the current byte is non-zero, the bits that are set correspond to clusters that are visible from this cluster. Continue until the number of clusters in the map is reached.
Example C code to decompress the bit vectors can be found in the "Quake 2 BSP File Format" document.
The maximum size of the Visibility lump is 0x1000000 bytes (MAX_MAP_VISIBILITY); that is, 16 Mb.
=== Entity ===
:See also: 
The entity lump (Lump 0) is an ASCII text buffer which stores the entity data in a format very similar to the format of uncompiled files. Its general form is:
{
	"world_maxs" "480 480 480"
	"world_mins" "-480 -480 -224"
	"maxpropscreenwidth" "-1"
	"skyname" "sky_wasteland02"
	"classname" "worldspawn"
}
{
	"origin" "-413.793 -384 -192"
	"angles" "0 0 0"
	"classname" "info_player_start"
}
{
	"model" "*1"
	"targetname" "secret_1"
	"origin" "424 -1536 1800"
	"Solidity" "1"
	"StartDisabled" "0"
	"InputFilter" "0"
	"disablereceiveshadows" "0"
	"disableshadows" "0"
	"rendermode" "0"
	"renderfx" "0"
	"rendercolor" "255 255 255"
	"renderamt" "255"
	"classname" "func_brush"
}
Entities are defined between opening and closing braces ({ and }) and list on each line a pair of key/value properties inside quotation marks. The first entity is always . The classname property gives the entity type, and the property gives the entity's name as defined in Hammer (if it has one). The model property is slightly special if it starts with an asterisk (*), the following number is an index into the model array (see above) which corresponds to a 'model'. Otherwise, the value contains the name of a compiled . Other key/value pairs correspond to the properties of the entity as set in Hammer.
Depending on the Source engine version, the entity lump can contain 4096 (Source 2004) to 16384 (Alien Swarm) entities (MAX_MAP_ENTITIES). These limits are independent from the engine's actual .
Each key can be a maximum of 32 characters (MAX_KEY) and the value up to 1024 characters (MAX_VALUE).
=== Game lump ===
The Game lump (Lump 35) seems to be intended to be used for map data that is specific to a particular game using the Source engine, so that the file format can be extended without altering the previously defined format. It starts with a game lump header:
struct dgamelumpheader_t
{
	int lumpCount;	// number of game lumps
	dgamelump_t gamelump[lumpCount];
};
where the gamelump directory array is defined by:
struct dgamelump_t
{
	int		id;		// gamelump ID
	unsigned short	flags;		// flags
	unsigned short	version;	// gamelump version
	int		fileofs;	// offset to this gamelump
	int		filelen;	// length
};
The gamelump is identified by the 4-byte id member, which defines what data is stored in it, and the byte position of the data and its length is given in fileofs and filelen. Note that fileofs is relative to the beginning of the BSP file, not to the game lump offset. One exception is the console version of Portal 2, where fileofs is relative to the game lump offset, as one would expect.
==== Static props ====
Of interest is the gamelump which is used to store entities, which uses the gamelump ID of 'sprp' ASCII (1936749168 decimal). Unlike most other entities, static props are not stored in the entity lump. The gamelump formats used in Source are defined in the public/gamebspfile.h header file.
The first element of the static prop game lump is the dictionary; this is an integer count followed by the list of model (prop) names used in the map:
struct StaticPropDictLump_t
{
	int	dictEntries;
	char	name[dictEntries];	// model name
};
Each name entry is 128 characters long, null-padded to this length.
Following the dictionary is the leaf array:
struct StaticPropLeafLump_t
{
	int leafEntries;
	unsigned short	leaf[leafEntries];
};
Presumably, this array is used to index into the leaf lump to locate the leaves that each prop static is located in. Note that a prop static may span several leaves.
Next, an integer giving the number of StaticPropLump_t entries, followed by that many structures themselves:
struct StaticPropLump_t
{
	// v4
	Vector		Origin;		 // origin
	QAngle		Angles;		 // orientation (pitch roll yaw)
	unsigned short	PropType;	 // index into model name dictionary
	unsigned short	FirstLeaf;	 // index into leaf array
	unsigned short	LeafCount;
	unsigned char	Solid;		 // solidity type
	unsigned char	Flags;
	int		Skin;		 // model skin numbers
	float		FadeMinDist;
	float		FadeMaxDist;
	Vector		LightingOrigin; // for lighting
	// since v5
	float		ForcedFadeScale; // fade distance scale
	// v6 and v7 only
	unsigned short MinDXLevel; // minimum DirectX version to be visible
	unsigned short MaxDXLevel; // maximum DirectX version to be visible
 // since v8
	unsigned char MinCPULevel;
	unsigned char MaxCPULevel;
	unsigned char MinGPULevel;
	unsigned char MaxGPULevel;
 // since v7
 color32 DiffuseModulation; // per instance color and alpha modulation
 // since v10
 float unknown; 
 // since v9
 bool DisableX360; // if true, don't show on XBox 360
};
The coordinates of the prop are given by the Origin member; its orientation (pitch, roll, yaw) is given by the Angles entry, which is a 3-float vector. The PropType element is an index into the dictionary of prop model names, given above. The other elements correspond to the location of the prop in the BSP structure of the map, its lighting, and other entity properties as set in Hammer. The other elements (ForcedFadeScale, etc.) are only present in the static prop structure if the gamelump's specified version is high enough (see dgamelump_t.version); both version 4 and version 5 static prop gamelumps are used in official HL2 maps. Version 6 has been encountered in TF2. Version 7 is used in some Left 4 Dead maps, and a modified version 7 is present in maps. Version 8 is used predominantly in , and version 9 in . The new version 10 appears in Tactical Intervention.
==== Other ====
Other gamelumps used in Source BSP files are the detail prop gamelump (dprp), and the detail prop lighting lump (dplt for LDR and dplh for HDR). These are used for entities (grass tufts, etc.) automatically emitted by certain textures when placed on displacement surfaces.
There does not seem to be a specified limit on the size of the game lump.
=== Displacements ===
Displacement surfaces are the most complex parts of a BSP file, and only part of their format is covered here. Their data is split over a number of different data lumps in the file, but the fundamental reference to them is through the dispinfo lump (Lump 26). Dispinfos are referenced from the face, original face, and brushside arrays.
==== DispInfo ====
struct ddispinfo_t
{
	Vector			startPosition;		// start position used for orientation
	int			DispVertStart;		// Index into LUMP_DISP_VERTS.
	int			DispTriStart;		// Index into LUMP_DISP_TRIS.
	int			power;			// power - indicates size of surface (2^power	1)
	int			minTess;		// minimum tesselation allowed
	float			smoothingAngle;		// lighting smoothing angle
	int			contents;		// surface contents
	unsigned short		MapFace;		// Which map face this displacement comes from.
	int			LightmapAlphaStart;	// Index into ddisplightmapalpha.
	int			LightmapSamplePositionStart;	// Index into LUMP_DISP_LIGHTMAP_SAMPLE_POSITIONS.
	CDispNeighbor		EdgeNeighbors[4];	// Indexed by NEIGHBOREDGE_ defines.
	CDispCornerNeighbors	CornerNeighbors[4];	// Indexed by CORNER_ defines.
	unsigned int		AllowedVerts[10];	// active verticies
};
The structure is 176 bytes long. The startPosition element is the coordinates of the first corner of the displacement. DispVertStart and DispTriStart are indices into the DispVerts and DispTris lumps. The power entry gives the number of subdivisions in the displacement surface - allowed values are 2, 3 and 4, and these correspond to 4, 8 and 16 subdivisions on each side of the displacement surface. The structure also references any neighbouring displacements on the sides or the corners of this displacement through the EdgeNeighbors and CornerNeighbors members. There are complex rules governing the order that these neighbour displacements are given; see the comments in bspfile.h for more. The MapFace value is an index into the face array and is face that was turned into a displacement surface. This face is used to set the texture and overall physical location and boundaries of the displacement.
==== DispVerts ====
The DispVerts lump (Lump 33) contains the vertex data of the displacements. It is given by:
struct dDispVert
{
	Vector	vec;	// Vector field defining displacement volume.
	float	dist;	// Displacement distances.
	float	alpha;	// "per vertex" alpha values.
};
where vec is the normalized vector of the offset of each displacement vertex from its original (flat) position; dist is the distance the offset has taken place; and alpha is the alpha-blending of the texture at that vertex.
A displacement of power p references (2^p 1)^2 dispverts in the array, starting from the DispVertStart index.
==== DispTris ====
The DispTris lump (Lump 48) contains "triangle tags" or flags related to the properties of a particular triangle in the displacement mesh:
struct dDispTri
{
	unsigned short Tags;	// Displacement triangle tags.
};
where the flags are:
Name 	Value
DISPTRI_TAG_SURFACE 	0x1
DISPTRI_TAG_WALKABLE 	0x2
DISPTRI_TAG_BUILDABLE 	0x4
DISPTRI_FLAG_SURFPROP1	0x8
DISPTRI_FLAG_SURFPROP2	0x10
There are 2x(2^p)^2 DispTri entries for a displacement of power p. They are presumably used to indicate properties for each triangle of the displacement such as whether the surface is walkable at that point (not too steep to climb).
There are a limit of 2048 Dispinfos per map, and the limits of DispVerts and DispTris are such that all 2048 displacements could be of power 4 (maximally subdivided).
Other displacement-related data are the DispLightmapAlphas (Lump 32) and DispLightmapSamplePos (Lump 34) lumps, which seem to relate to lighting of each displacement surface.
=== Pakfile ===
The Pakfile lump (Lump 40) is a special lump that can contains multiple files which are embedded into the bsp file. Usually, they contain special texture (.vtf) and material (.vmt) files which are used to store the reflection maps from env_cubemap entities in the map; these files are built and placed in the Pakfile lump when the buildcubemaps console command is executed. The Pakfile can optionally contain such things as custom textures and prop models used in the map, and are placed into the bsp file by using the program (or alternate programs such as ). These files are integrated into the game engine's file system and will be loaded preferentially before externally located files are used.
The format of the Pakfile lump is identical to that used by the Zip compression utility when no compression is specified (i.e., the individual files are stored in uncompressed format). If the Pakfile lump is extracted and written to a file, it can therefore be opened with WinZip and similar programs.
The header public/zip_uncompressed.h defines the structures present in the Pakfile lump. The last element in the lump is a ZIP_EndOfCentralDirRecord structure. This points to an array of ZIP_FileHeader structures immediately preceeding it, one for each file present in the Pak. Each of these headers then point to ZIP_LocalFileHeader structures that are followed by that file's data.
The Pakfile lump is usually the last element of the bsp file.
=== Cubemap ===
The Cubemap lump (Lump 42) is an array of 16-byte dcubemapsample_t structures:
struct dcubemapsample_t
{
	int		origin[3];	// position of light snapped to the nearest integer
	int	 size;		// resolution of cubemap, 0 - default
};
The dcubemapsample_t structure defines the location of a env_cubemap entity in the map. The origin member contains integer x,y,z coordinates of the cubemap, and the size member is resolution of the cubemap, specified as 2^(size-1) pixels square. If set as 0, the default size of 6 (32x32 pixels) is used. There can be a maximum of 1024 (MAX_MAP_CUBEMAPSAMPLES) cubemaps in a file.
When the "buildcubemaps" console command is performed, six snapshots of the map (one for each direction) are taken at the location of each env_cubemap entity. These snapshots are stored in a multi-frame texture (vtf) file, which is added to the Pakfile lump (see above). The textures are named cX_Y_Z.vtf, where (X,Y,Z) are the (integer) coordinates of the corresponding cubemap.
Faces containing materials that are environment mapped (e.g. shiny textures) reference their assigned cubemap through their material name. A face with a material named (e.g.) walls/shiny.vmt is altered (new Texinfo & Texdata entries are created) to refer to a renamed material maps/mapname/walls/shiny_X_Y_Z.vmt, where (X,Y,Z) are the cubemap coordinates as before. This .vmt file is also stored in the Pakfile, and references the cubemap .vtf file through its $envmap property.
Version 20 files contain extra cX_Y_Z.hdr.vtf files in the Pakfile lump, containing HDR texture files in RGBA16161616F (16-bit per channel) format.
=== Overlay ===
Unlike the simpler decals (infodecal entities), info_overlays are removed from the entity lump and stored separately in the Overlay lump (Lump 45). The structure is reflects the properties of the entity in Hammer almost exactly:
struct doverlay_t
{
	int		Id;
	short		TexInfo;
	unsigned short	FaceCountAndRenderOrder;
	int		Ofaces[OVERLAY_BSP_FACE_COUNT];
	float		U[2];
	float		V[2];
	Vector		UVPoints[4];
	Vector		Origin;
	Vector		BasisNormal;
};
The FaceCountAndRenderOrder member is split into two parts; the lower 14 bits are the number of faces that the overlay appears on, with the top 2 bits being the render order of the overlay (for overlapping decals). The Ofaces array, which is 64 elements in size (OVERLAY_BSP_FACE_COUNT) are the indices into the face array indicating which map faces the overlay should be displayed on. The other elements set the texture, scale, and orientation of the overlay decal. There can be a maximum of 512 overlays per file (MAX_MAP_OVERLAYS). In Dota 2 this limit on the number of overlays is increased significantly.
=== Lighting ===
The lighting lump (Lump 8) is used to store the static lightmap samples of map faces. Each lightmap sample is a colour tint that multiplies the colours of the underlying texture pixels, to produce lighting of varying intensity. These lightmaps are created during the VRAD phase of map compilation and are referenced from the dface_t structure. The current lighting lump version is 1.
Each dface_t may have a up to four lightstyles defined in its styles[] array (which contains 255 to represent no lightstyle). The number of luxels in each direction of the face is given by the two LightmapTextureSizeInLuxels[] members (plus 1), and the total number of luxels per face is thus:
(LightmapTextureSizeInLuxels[0] + 1) * (LightmapTextureSizeInLuxels[1] + 1)
Each face gives a byte offset into the lighting lump in its lightofs member (if no lighting information is used for this face e.g. faces with skybox, nodraw and invisible textures, lightofs is -1.) There are (number of lightstyles)*(number of luxels) lightmap samples for each face, where each sample is a 4-byte ColorRGBExp32 structure:
struct ColorRGBExp32
{
	byte r, g, b;
	signed char exponent;
};
Standard RGB format can be obtained from this by multiplying each colour component by 2^(exponent). For faces with bumpmapped textures, there are four times the usual number of lightmap samples, presumably containing samples used to compute the bumpmapping.
Immediately preceeding the lightofs-referenced sample group, there are single samples containing the average lighting on the face, one for each lightstyle, in reverse order from that given in the styles[] array.
Version 20 BSP files contain a second, identically sized lighting lump (Lump 53). This is presumed to store more accurate (higher-precision) HDR data for each lightmap sample. The format is currently unknown, but is also 32 bits per sample.
The maximum size of the lighting lump is 0x1000000 bytes, i.e. 16 Mb (MAX_MAP_LIGHTING).
=== Occlusion ===
The occlusion lump (Lump 9) contains the polygon geometry and some flags used by entities. Unlike other brush entities, func_occluders don't use the 'model' key in the entity lump. Instead, the brushes are split from the entities during the compile process and numeric occluder keys are assigned as 'occludernum'. Brush sides textured with tools/toolsoccluder or tools/toolstrigger are then stored together with the occluder keys and some additional info in this lump.
The lump is divided into three parts and begins with a integer value with the total number of occluders, followed by an array of doccluderdata_t fields of the same size.
The next part begins with another integer value, this time for the total number of occluder polygons, as well as an array of doccluderpolydata_t fields of equal size. Part three begins with another integer value for the amount of occluder polygon vertices, followed by an array of integer values for the vertex indices, again of the same size.
struct doccluder_t
{
	int			count;
	doccluderdata_t		data[count];
	int			polyDataCount;
	doccluderpolydata_t	polyData[polyDataCount];
	int			vertexIndexCount;
	int			vertexIndices[vertexIndexCount];
};
The doccluderdata_t structure contains flags and dimensions of the occluder, as well as the area where it remains.
firstpoly is the first index into the doccluderpolydata_t with a total of polycount entries.
struct doccluderdata_t
{
	int	flags;
	int	firstpoly;	// index into doccluderpolys
	int	polycount;	// amount of polygons
	Vector	mins;	 // minima of all vertices
	Vector	maxs;	 // maxima of all vertices
	// since v1
	int	area;
};
Occluder polygons are stored in the doccluderpolydata_t structure and contain the firstvertexindex field, which is the first index into the vertex array of the occluder, which are again indices for the vertex array of the vertex lump (Lump 3). The total number of vertex indices is stored in vertexcount.
struct doccluderpolydata_t
{
	int	firstvertexindex;	// index into doccludervertindices
	int	vertexcount;		// amount of vertex indices
	int	planenum;
};
=== Other ===
*The Worldlights lump (Lump 15) contains information on each static light entity in the world, and seems to be used to provide semi-dynamic lighting for moving entities.
*The Areas lump (Lump 20) references the Areaportals lump (Lump 21) and is used with func_areaportal and func_areaportalwindow entities to define sections of the map that can be switched to render or not render.
*The Portals (Lump 22), Clusters (Lump 23), PortalVerts (Lump 24), ClusterPortals (Lump 25), and ClipPortalVerts (Lump 41) lumps are used by the VVIS phase of the compile to ascertain which clusters can see which other clusters. A cluster is a player-enterable leaf volume in the map (see above). A "portal" is a polygon boundary between a cluster or leaf and an adjacent cluster or leaf. Most of this information is also used by the VRAD program to calculate static lighting, and then is removed from the bsp file.
*PhysCollide Lumps (Lump 29) and PhysCollideSurface (Lump 49) lumps seem to be related to the physical simulation of entity collisions in the game engine.
*The VertNormal (Lump 30) and VertNormalIndices (Lump 31) lumps may be related to smoothing of lightmaps on faces.
*The FaceMacroTextureInfo lump (Lump 47) is a short array containing the same number of members as the number of faces in the map. If the entry for a face contains anything other than -1 (0xFFFF), it is an index of a texture name in the TexDataStringTable. In VRAD, the corresponding texture is mapped onto the world extents, and used to modulate the lightmaps of that face. There is also a base macro texture (located at materials/macro/mapname/base.vtf) that is applied to all faces if found. Only maps in VTMB seem to make any use of macro textures.
*LeafWaterData (Lump 36) and LeafMinDistToWater (Lump 46) lumps may be used to determine player position with respect to water volumes.
*The Primitives (Lump 37), PrimVerts (Lump 38) and PrimIndices (Lump 39) lumps are used in reference to "non-polygonal primitives". They are also sometimes called "waterstrips", "waterverts" and "waterindices" in the SDK Source, since they were originally only used to subdivide water meshes. They are now used to prevent the appearance of cracks between adjacent faces, if the face edges contain a "T-junction" (a vertex collinearly between two other vertices). The PrimIndices lump defines a set of triangles between face vertices, that tessellate the face. They are referenced from the Primatives lump, which is in turn referenced by the face lump data. Current maps do not seem to use the PrimVerts lump at all. (Ref.)
*Version 20 files containing HDR lighting information have four extra lumps, the contents of which are currently uncertain. Lump 53 is always the same size as the standard lighting lump (Lump 8) and probably contains higher-precision data for each lightmap sample. Lump 54 is the same size as the worldlight lump (Lump 15) and presumably contains HDR-related data for each light entity. Lumps 55 and 56 both seem to be 24-byte records (possibly CompressedLightCube structures) with the same count as the number of leaves in the map. They are probably thus HDR-related per-leaf lighting information.