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GameDatakey must be present in gameinfo.txt pointing to the game's FGD file. Only Left 4 Dead 2 and later, along with Team Fortress 2, include this by default. Instances can be enabled in other games by adding this, or using a pre-compiler as described below.
Instances are helpful in many ways:
- They provide a more dynamic alternative to prefabs, as any changes to the instanced map will be reflected in all instances of it.
- They provide an alternative to visgroups, as they can be used to divide a large, unwieldy map into several smaller, manageable ones (that can even be worked on by multiple authors simultaneously).
- They provide a simple way to edit portions of a map that needs to be at a non-orthogonal angle. (Build the map on-grid inside a separate map, and then instance it into another map through a func_instance rotated at the correct angle.
- They provide a way for maps to work on multiple platforms, such as Left 4 Dead and Left 4 Dead 2 versions of the same map.
In Left 4 Dead 2 and later, instances can send and receive inputs and outputs. To use this functionality, a
func_instance_io_proxy entity named
proxy must be present and properly configured in the instance. To send an input to an entity within the instance, the following output would be used:
To receive an output from an entity in the instance, this output would be used on the
In older branches
Pre-L4D2 engine branches do not support the instance I/O system, so workarounds are needed to send and receive inputs and outputs in instances. For inputs, the fixed up entity name can be referenced directly.
Instances can be taken a step further with manifests. A manifest splits all of the contents of a map into special instances known as "sub-maps". Unlike regular instances, Hammer can seamlessly switch between sub-maps without having to open the VMFs separately. Sub-maps are treated as extensions of the map itself and cannot use name fixup or have any offset, although sub-maps are capable of being used in multiple manifests simultaneously.
Manifests can be helpful in many ways:
- They allow multiple people to work on a map at the same time.
- They help protect a map against corruption, as problems with a VMF are limited to a single sub-map.
- They can be used to assign user-friendly names to different areas of a map.
- They can make a map's source files easier to track in version control software like Git.
A manifest can be created in the "Instancing" menu.
Metapyziks wrote a program that merges instances into the main VMF before each compile. This was originally created to enable instance support in older engine branches, but the
GameData method has since rendered it mostly obsolete. However, it would theoretically be possible for someone to fork the program to add additional functionality, such as instance I/O support or the ability to toggle VisGroups with a fixup variable.
- L4D2 Level Design/VMF Instances - A Valve tutorial on how to use instances in Left 4 Dead 2.
- Working with instances - A tutorial on how to use instances in Portal 2.