Introduction to data modifications

Reading time: 8 min

Now that you have a basic understanding of how Frostbite data is structured and the terminology surrounding it let's look at how we can use VeniceEXT to use it or modify it. In this guide we'll cover basic modifications and some more advanced use-cases.

Data representation in VeniceEXT

In the Frostbite data basics guide we mentioned partitions and instances. Both of these are represented in VeniceEXT through its type system. More specifically, partitions are represented by the DatabasePartition type and instances by the DataContainer type (and anything that inherits from it). It's pretty common that VeniceEXT will provide you an instance of a specific type as a DataContainer object and then you'll have to cast it to a more specific type. We'll see an example of that below.

Modifying instances

Let's look at how we can modify instances. Every time the engine loads a partition, the Partition:Loaded event gets dispatched with a DatabasePartition object passed to it. As we mentioned, the DatabasePartition type represents a Frostbite partition and the instances contained within it. We can iterate through its instances property to go through all the partitions contained within it and modify the one we want.

Let's look at an example where we modify the height ceiling (the max height vehicles can fly to) for any loaded level:

Events:Subscribe('Partition:Loaded', function(partition)
  for _, instance in pairs(partition.instances) do
    if instance:Is('LevelData') then
      local levelDataInstance = LevelData(instance)

      levelDataInstance.maxVehicleHeight = 999999

Let's walk through what we're doing in the example above. As we mentioned above, every time a partition is loaded, the Partition:Loaded event gets called. We register a handler for that event and when it's called we iterate through all the instances contained within the partition. Every instance is of the DataContainer type so we use the Is method on it to check if it's a more specific type by passing the name of the type we want to check against. In this case, we check if an instance is of the LevelData type, which is the instance type that contains information about a specific level. If it is, then we cast it to that type so we can later modify its properties.

Now, before we can modify it we need to call the MakeWritable method on it. That's because instances loaded from data will by default be read-only (you can also use the isReadOnly property to check but it's not necessary, since MakeWritable will just do nothing if the instance is not read-only). After making it writable, we can then modify the maxVehicleHeight property. In this case we're setting it to 999999, effectively getting rid of the flight ceiling. As calling MakeWritable is quite expensive, you should only call it on instances you plan to modify.

Now, keep in mind that you generally want to do changes like these inside a shared script so changes are applied on both the server and the client. In some cases, if we only modify data on one side then players will be kicked upon joining a server because their data will not match.

Waiting for instances to load

In the example above, we go through every single instance to find the one we need. This can be a bit wasteful at times, so VeniceEXT provides us with a way to notify us when a specific instance has loaded. If you know the Guid of an instance and the Guid of the partition it's in, you can use the ResourceManager:RegisterInstanceLoadHandler and ResourceManager:RegisterInstanceLoadHandlerOnce library methods to have VeniceEXT call a function you provide as soon as said instance is loaded. Let's look at an example:

ResourceManager:RegisterInstanceLoadHandler(Guid('707F4A91-B837-47AC-8BEE-5EB614399714'), Guid('A83D8333-F6D5-43AA-BA65-96122FAE8F7C'), function(instance)
  local levelDataInstance = LevelData(instance)

  levelDataInstance.maxVehicleHeight = 999999

In this example we register a callback for the XP3_Alborz LevelData instance by passing the Guid of the partition its contained in as the first parameter, the Guid of the instance itself as the second parameter, and our callback as the third. When this instance gets loaded our function will be called and we'll modify the instance just like we did in the previous example.

Keep in mind that this callback will remain active until you deregister it (we'll show how to do that below). If you only want the callback to be called the first time an instance loads you can use the RegisterInstanceLoadHandlerOnce method, which will automatically deregister the callback as soon as it's called.

Deregistering callbacks

Calls to the RegisterInstanceLoadHandler and RegisterInstanceLoadHandlerOnce methods return a ContainerCallback object. If you wish for your callback function to no longer get called when the specified instance gets loaded, you can store that object and call the Deregister method on it as seen below:

local ctrCb = ResourceManager:RegisterInstanceLoadHandler(...)

-- At some later point.


Callback user data

Similar to event callbacks, you can pass custom user data to the RegisterInstanceLoadHandler and RegisterInstanceLoadHandlerOnce method to be passed back to your callback function when it's called:

local x = 123

ResourceManager:RegisterInstanceLoadHandler(Guid('707F4A91-B837-47AC-8BEE-5EB614399714'), Guid('A83D8333-F6D5-43AA-BA65-96122FAE8F7C'), x, function(userData, instance)

In the example above we pass the variable x before the callback function. When the callback function is called, its value will be passed as the first parameter to the callback function (in this case named userData) and will be printed (in this case 123 will be printed).

Lazy-loaded instances

Sometimes when trying to cast an instance from the DataContainer type to something more specific, you may get the following error:

cannot cast an instance that's lazy loaded to 'X'

That happens for instances that are referenced by other instances but have not yet been loaded by the engine and will be loaded at some point in the future. We call these “lazy-loaded” instances. You can check if an instance is being lazy-loaded by checking the value of the isLazyLoaded property. Additionally, if you want to be notified when this instance gets loaded, you can use the RegisterLoadHandler and RegisterLoadHandlerOnce methods which work similarly to the ResourceManager methods we demonstrated above:

if someInstance.isLazyLoaded then
    print('Instance has loaded!')
    -- Do something with loadedInstance.

In this example, we assume that the someInstance variable is a DataContainer object and we check if it's being lazy-loaded. If it is, then we register a callback function to be called once after it's loaded, which will print Instance has loaded! as soon as it has.

Searching for instances

Sometimes you might need to find an instance to use for some purpose (eg. creating an entity). Your first instinct might be to register a Partition:Loaded event, and store it as soon as you encounter it to use later. However, VeniceEXT provides some tools to look up instances on demand. We'll look at the different ways you can do that.

Searching by name

Some instances have a name associated to them. These are primarily instances that are of the Asset type (and any of its derivates). You can use the ResourceManager:SearchForDataContainer library method to search for them by their name:

local instance = ResourceManager:SearchForDataContainer('Levels/XP3_Alborz/XP3_Alborz')

In this example, we look up the instance with the name Levels/XP3_Alborz/XP3_Alborz, which is the same LevelData instance we were registering a load handler for before. If you look at the dump of this instance you'll see that its name field has a value of Levels/XP3_Alborz/XP3_Alborz which is what we're using to look it up.

Searching by instance Guid

If you know the Guid of an instance you can use the ResourceManager:SearchForInstanceByGuid library method to look it up by it:

local instance = ResourceManager:SearchForInstanceByGuid(Guid('A83D8333-F6D5-43AA-BA65-96122FAE8F7C'))

Searching by partition & instance Guid

Searching by name or just by instance Guid can be a bit slow. If you know both the partition Guid and the instance Guid you can use the ResourceManager:FindInstanceByGuid library method to look an instance up a lot faster:

local instance = ResourceManager:FindInstanceByGuid(Guid('707F4A91-B837-47AC-8BEE-5EB614399714'), Guid('A83D8333-F6D5-43AA-BA65-96122FAE8F7C'))

Creating new instances

Sometimes you may want to create your own instances for a specific purpose (eg. creating a variation of something that already exists or creating something completely new). There are two ways to do that using VeniceXT that we'll explain below.

Cloning instances

The first and easiest is by cloning an instance that already exists. Cloning essentially creates an exact shallow copy of an instance. Shallow copy is basically the equivalent of creating a new instance of that type and assigning each of its fields to the values of the original instance one-by-one. That means that if you have a field that references another instance, the new instance clone will still point to the same thing instead of cloning the referenced instance as well. You can clone instances by using the Clone method on them, as seen below:

local clonedInstance = someInstance:Clone()

In this example we assume that the someInstance variable holds an instance (DataContainer object). The result of the Clone method call (clonedInstance) will be a new instance with all the same properties as someInstance.

Additionally, you can pass a Guid to the Clone method to associated that Guid with the newly created instance. You can also add it to a partition by using the AddInstance method of the DatabasePartition type. Doing that allows you to later use that Guid to look it up via the methods we mentioned above or make it discoverable for other mods to use.

Creating instances by type

You can also create instances by their type. Every instance type has two constructors: one that takes no arguments and one that takes a Guid as an argument. The latter functions similarly to the Clone method we mentioned above, in that it will associate that Guid with the newly created instance. Let's look at an example:

local data = PointLightEntityData()

data.width = 10
data.color = Vec3(1, 0, 0)
data.radius = 10
data.visible = true

In this example we create a new instance of the PointLightEntityData type and assign some values to some of its properties. We can then use this instance to spawn a point light entity (which we'll cover in the Entities guide).

Next up, see how entities work, how to spawn them, find them, and work with them.

Last modified September 25, 2020: Fix typo in datamod guide (78da1a2)