L4D Campaign Add-On Tutorial
There are five basic steps to creating your own custom campaign Add-ons for Left 4 Dead:
- Make an Add-on folder and content sub-folders.
- Create game assets and place them in the proper sub-folder.
- Create metadata files and place them in the proper sub-folder.
- Pack the contents of the Add-on folder into a VPK file.
- Create a homepage for the add-on where it can be downloaded by players.
Install the Authoring Tools
In order to author content for Left 4 Dead, you will need to install the Left 4 Dead Authoring Tools. This provides you with the applications and utilities you will need to create game content. Mainly, you will be using the Hammer application to create levels, and the other utilities to create custom textures and models.
A description of how to create these assets is beyond the scope of this tutorial, but you can find useful information in the L4D Level Design Basics Tutorial. Because the focus of this article is how to assemble the assets into a campaign Add-on, we will assume that you have already learned how to successfully create these assets from this point forward.
The Authoring Tools provides an example Add-on campaign called Dead Line that has source examples.
Create an Add-On Folder
To begin, navigate to theaddonsfolder of your Left 4 Dead game install location. For most users, this will be similar to:
C:\Program Files\Steam\steamapps\common\left 4 dead\left4dead\addons
Note:If you have a folder with a hyphen, i.e., "add-ons," make sure it's empty and go ahead and delete it. The correct folder has no hyphen: "addons." Make a new folder inside the "addons" directory, and give it an appropriate name. This new folder will be the name of the VPK file you'll ultimately create and distribute, so it's good practice to avoid spaces and use all lowercase letters. You may also include the game in the title, to differentiate it from add-ons for other titles, and optionally a version number. We'll use "deadline" instead of "l4d_deadline" for our example for the sake of readability.
…\left4dead\addons\deadline
Conceptually, this add-on folder will serve as the base “game” folder for your assets, and will mirror the layout in the shipped VPK files as we shall see below.
Create Primary Game Assets
The assets you create will essentially append those shipped with the game. For a campaign, the primary assets are the BSP and NAV files for your map levels.
Make a folder called maps inside your add-on project folder:
…\left4dead\addons\deadline\maps
Into this maps folder, copy the BSP and NAV files you're using for your maps. For this Dead Line tutorial example, there are three map file.bsp/.navpairs:
| File | Description |
|---|---|
l4d_deadline01
|
Minimal starting map for co-op |
l4d_deadline02
|
Final map for co-op, survival |
l4d_deadline02_vs
|
A variation of the above map that includes modifications designed for with versus mode |
The advantage of having a single map function for multiple game modes is size reduction, which can be worth the additional authoring complexity.
You may also optionally create custom VTF texture images, custom VMT material description files, and custom MDL models which your maps can utilize. In order to keep the size of your add-on small, it's advisable to use as many textures and models from the game as possible.
Additional VMT and VTF materials (see Creating a Material) should go under this folder:
…\left4dead\addons\deadline\materials
MDL and related model files (see exporting and compiling a model) should go under here:
…\left4dead\addons\deadline\models
And materials for your models should go under here:
…\left4dead\addons\deadline\materials\models
It should be noted that L4D treats the/deadlinefolder much the same way as the/left4deadfolder, so any folders you use inside the materials and models that you employ must also be present in your campaign's folder.
Create Secondary Game Assets
Secondary assets such as poster and thumbnail images are not strictly required, but they can give your campaigns an extra level of polish. (Besides, the poster/concept art was likely the first thing you created, wasn't it?) If you haven't already, go ahead and make amaterialsfolder and avguifolder inside of it:
...\left4dead\addons\deadline\materials\vgui
Campaign Poster
Inside thevguifolder, you'll want to place at least two VTF files, along with VMTs that reference them:
LoadingScreen_DeadLine.vtf- This is a poster image that is displayed while your campaign loads. Standard size is 1024 x 1024 pixels with an alpha channel for transparency.
OutroTitle_DeadLine.vtf- This is a title image that appears behind the end credits/stats. Standard size is 1024 x 256 pixels. Your design should look good against a black background and also allow white text in the foreground to be readable.
Map Thumbnail Previews
In addition to these two, you'll also want to make thumbnail images for each map in your campaign. These serve to provide a visual reinforcement indication for users while they're selecting map "chapters" in the UI.
To do so, create a new folder namedmapsunder thevguifolder:
…\left4dead\addons\deadline\materials\vgui\maps
In this folder, you'll want to create a VTF/VMT pair for each map you wish to create. They should each be 256 by 128 pixels. If appropriate, you may use a single thumbnail image to represent multiple BSP maps, such as when you have a versus or survival variant of the same level.
VMT files which are used for interface elements such as posters, thumbnails, etc. (i.e., those typically found in thematerials/vguifolder,), often need to specify an UnlitGeneric material. See Deadline vgui .VMT File for an example.
Create Metadata Files
There are a few more files that you will make in order to allow your add-on content to function in game.
addoninfo.txt
The first is theaddoninfo.txtfile. This allows your content to be recognized by the game. It should go inside your add-on root folder, which was the first one we created way back at the top:
…\left4dead\addons\deadline\addoninfo.txt
This file is used by the game in the Extras > Add-ons screen. It describes your add-on in general and what it provides. The example Deadline AddonInfo File includes full comments and instructions for using it as a template for your own add-on.
addonimage.jpg
Another file you can create in the root folder is an image named 
addonimage.jpg. This serves as an icon/thumbnail to help differentiate your add-on and is displayed when an add-on is selected in the UI along with add-on details listed in the addoninfo.txt. Some JPG files may not work, depending on which application they are saved from (such as 
Adobe Photoshop). If you're having trouble getting your JPG to work, try importing and exporting it from VTFEdit. It is recommended (but not required) that the image is in widescreen resolution.
Mission File
The second required file is the mission file. This describes the structure and content of your campaign and is used by the campaign selection UI, matchmaking, and the game server. This should be a TXT file with a unique name in the missions folder, which you will also need to make:
...\left4dead\addons\deadline\missions\deadline.txt
The example Deadline Mission File includes full comments and instructions for using it as a template for your own mission.
Test It Out
At this point, your add-on should be fully functional. You should be able to launch the game, go to Extras->Add-ons, and enable your add-on. If you type path into the console, you should see the root directory of your add-on near the bottom. This means that the game will search your add-on folder for files that it cannot find in the standard game VPK files. You can continue tweaking your content in folder form until you're ready for that magical moment: Release into the wild.
Packaging and Shipping
The final remaining step is to package your add-on into a VPK for distribution.
The VPK serves as a convenient, one file method for others to install your add-on folder. They need simply put the .VPK in their own add-on folder. Or, assuming they, like most non-authoring players, haven't associated the .VPK extension with something else, they can double click on it and it will install itself in the correct place.
Every VPK file contains a unique ID that allows the game to ensure everyone is running the same content. If you've put in meta-data properly, the game will also prompt users to download a newer version if it is required to play.
Navigate to this folder:
C:\Program Files\Steam\steamapps\common\left 4 dead\bin\
Locate the vpk.exe packaging utility and make a shortcut to it on your desktop. Drag your add-on root folder and drop it onto the shortcut. The utility should make a new VPK next to your original folder. By default it will not include source files such as VMF, TGA, SMD, QC, etc., and it will always strip out executable binaries. Remove the folder version of the add-on (or move it to a safe location) so that the VPK is alone and test it out. The VPK should function exactly as the add-on folder does. If it works, you're ready to upload it to a location you specified in the metadata files and from which it is available.
Ideally, you'll want an add-on "homepage" that includes ratings, screenshots, and player comments. A simple example can be found here.
Compression
Since full Left 4 Dead campaigns can be very large, it is advisable to compress them before uploading to file sharing sites for distribution. The open-source Windows utility 7-zip supports compressing files in the 7z format/LZMA algorithm, which provide a very high compression ratio. The bulk of a campaigns size comes from the.bspmap files, which are highly compressible, so a.vpkcan be reduced to 25% or less of its original size. For example, an unofficial version of Death Aboard was packaged up by a fan; the.vpk was 267MB uncompressed, 92MB zipped, and 55MB with 7z.
Final Testing
At this point, you should test out the download prompt. Start a lobby with a local server, and invite a friend to join. When they accept, they should be prompted to download the necessary add-on, after which a browser window will opened to your add-on homepage. They should be able to download and install the add-on without having to restart the game, and then join your lobby.