Cubemaps
A cubemap is a texture that represents a three-dimensional rendering of an area. The Source Engine uses env_cubemap entities as sampling points for generating these textures, which are then saved into the map file. Once built, cubemaps will be reflected on surfaces that use the $envmap parameter with env_cubemap as its value.
Building cubemaps
Building cubemaps is the process of generating their textures for reflective effects. For technical reasons, this process is not automated and should be done by the user; until then, env_cubemaps will remain unused and the map, depending on the game, will display either generic or "missing" textures on reflections due to non-existent cubemaps.
Warning:Your game's resolution must be at least 4 times higher than the highest size of an env_cubemap in a map, or else attempting to build them will either fail or even cause the game to crash. For example: if an env_cubemap sizes 128x128, you'll need a resolution of at least 512x512 (128 × 4 = 512 -> 720x576 or higher).
Note:It's necessary to relaunch the game after building cubemaps in order to display them.
Tip:Maxing out your game's visual settings prior to building cubemaps will generate their textures in the best-possible quality (based on the env_cubemaps' size).
Before building
Counter-Strike: Source maps are among the known ones to include pre-built, blank cubemaps on compile; they're built even if there are no env_cubemaps in the map, and it is recommended to delete them first as explained here.
LDR
Note:This step doesn't apply to 
Counter-Strike: Global Offensive as its maps are compiled in HDR only.A map compiled in LDR (Low Dynamic Range) will build only that mode's cubemaps, regardless of your game's current HDR (High Dynamic Range) setting. Submit the following commands into the game's console:
| Command | Description |
|---|---|
mat_specular 0 |
Disables specularity. Required to properly build cubemaps |
map <the map's filename> |
Loads the map (e.g., map cs_mymap)
|
sv_cheats 1 |
Enables the use of cheat commands. Required to build cubemaps |
buildcubemaps |
Starts building cubemaps |
disconnect |
Unloads the map, returning you to the main menu |
mat_specular 1 |
Enables specularity. Required to see reflections |
quit |
(optional) Closes the game. Required to see reflections after building cubemaps |
HDR
A map compiled with HDR support will need its cubemaps built twice; once for each mode (HDR and LDR). As opposed to a LDR map's case, your game's HDR setting must be set to "None" to build LDR cubemaps, and to "Full" to build HDR ones. Submit the following commands into the game's console:
| Command | Description |
|---|---|
mat_specular 0 |
Disables specularity. Required to properly build cubemaps |
map <the map's filename> |
Loads the map (e.g., map cs_mymap)
|
sv_cheats 1 |
Enables the use of cheat commands. Required to build cubemaps |
buildcubemaps |
Starts building cubemaps |
sv_cheats 0 |
Disables cheat commands. Prevents command mat_reloadallmaterials from self-executing and briefly freezing the game unnecessarily
|
disconnect |
Unloads the map, returning you to the main menu |
mat_hdr_level 0 |
Switches to LDR mode (from HDR). Submit mat_hdr_level 2 instead if LDR cubemaps were built first
|
map <the map's filename> |
Loads the map again to build cubemaps for the new mode |
sv_cheats 1 |
|
buildcubemaps |
Starts building cubemaps for the new mode |
disconnect |
|
mat_specular 1 |
Enables specularity. Required to see reflections |
mat_hdr_level 0/1/2 |
If necessary, switches back to the mode it was before having submitted mat_hdr_level 0/2
|
quit |
(optional) Closes the game. Required to see reflections after building cubemaps |
Half-Life: Source
Bug:Cubemaps in 
Half-Life: Source currently don't build properly as their textures, despite being generated, aren't saved into the map file afterward. [todo tested in ?]
Workaround:Move the BSP file into the "maps" folder of a game of the same engine branch (such as 
Half-Life 2), build the cubemaps in that game, then move the file back into Half-Life: Source's.
Source Filmmaker
Bug:In 
Source Filmmaker, loading a map whose cubemaps were built in another game will display weird artifacts on reflections due to a sixth cubemap face that it doesn't seem to recognize (it uses only five of them). Rebuilding the cubemaps would fix the issue, but Source Filmmaker currently doesn't properly build cubemaps as their textures are generated blank. [todo tested in ?]- Workaround:Move the BSP file into
Alien Swarm's "maps" folder, build the cubemaps in said game, then move the file back into Source Filmmaker's.- Note:For this procedure, Alien Swarm's "gameinfo.txt" file will need to be edited to have access to assets from the mod directories within Source Filmmaker not to build cubemaps with missing textures/models. The file's "SearchPath" section should look like this:
"SearchPaths"
{
"Game" "|gameinfo_path|."
"Game" "swarm_base"
"Game" "platform"
"Game" "..\SourceFilmmaker\game\hl2"
"Game" "..\SourceFilmmaker\game\tf"
"Game" "..\SourceFilmmaker\game\tf_movies"
"Game" "..\SourceFilmmaker\game\usermod"
}
Deleting cubemaps
Deleting cubemaps gets rid of unnecessary or outdated ones and their associated files. Out of all other capable tools, BSPZIP is the safest way for doing so without potentially corrupting the map; from the "maps" folder (where the BSP file should be located), execute the following command:
..\..\bin\bspzip -deletecubemaps mapname.bsp
Note:Replace "mapname" with the map's actual filename.Warning:Cubemaps should be deleted before embedding texture (".vtf") files into the map file as this procedure actually deletes all of its embedded textures.Extracting cubemaps
In cases where a map needs to be updated (recompiled) with minor changes and its built cubemaps vanish as a result, extracting said cubemaps beforehand will make it not necessary to go through the whole cubemap-building process again until it actually becomes so. Create a folder that will contain the extracted cubemaps within the "maps" folder and execute the following command:
..\..\bin\bspzip -extractcubemaps mapname.bsp "foldername"
Note:Replace "mapname" with the map's actual filename, and "foldername" with the actual name of the folder to extract cubemaps into.
Embedding cubemaps
To make a map use extracted cubemaps, create a text file within the BSP file's location that will include paths to the cubemap textures to embed into it with the use of BSPZIP. Here's how such a file should look like:
materials/maps/mapname/c0_416_64.hdr.vtf foldername\materials\maps\mapname\c0_416_64.hdr.vtf materials/maps/mapname/c0_416_64.vtf foldername\materials\maps\mapname\c0_416_64.vtf materials/maps/mapname/c416_0_64.hdr.vtf foldername\materials\maps\mapname\c416_0_64.hdr.vtf materials/maps/mapname/c-416_0_64.hdr.vtf foldername\materials\maps\mapname\c-416_0_64.hdr.vtf materials/maps/mapname/c416_0_64.vtf foldername\materials\maps\mapname\c416_0_64.vtf materials/maps/mapname/c-416_0_64.vtf foldername\materials\maps\mapname\c-416_0_64.vtf materials/maps/mapname/cubemapdefault.vtf foldername\materials\maps\mapname\cubemapdefault.vtf
Note:Replace "mapname" with the map's actual filename, and "foldername" with the actual name of the folder that contains the extracted cubemaps.Two lines (paths) are required per file; the first line represents the directory structure that the file will take within the map file, while the second one is the actual path to the file to find and embed. In this example, the second lines use a relative path (considering that the text file is in the same directory as the folder with extracted cubemaps), though it can also be absolute. Once the text file is ready, execute the following comand:
..\..\bin\bspzip -addlist mapname.bsp textfile.txt newmapname.bsp
Note:Replace "mapname" with the map's actual filename, "textfile" with the text file's actual filename, and "newmapname" with the map's actual filename to override it (or type in a different one to generate an additional BSP file without overwriting the original).Renaming a map
The map's name is used for the directory where built cubemaps are saved into within the file; changing its name will cause the cubemaps not to load alongside the map, and therefore it will act as if there were none. To correct that, either delete and then rebuild the cubemaps, or extract and then repack (embed) them with the cubemaps' directory matching the map's new name.