Contexts
Each script runs in a context: the environment holding its global variables and functions. Which scripts share a context is decided by the context policy of the scripting plugin. By default each entity-script pair gets its own context, isolated from all other scripts.
Context policies
| Policy | Scripts sharing a context |
|---|---|
ContextPolicy::per_entity_and_script() (default) | None, the most isolated |
ContextPolicy::per_entity() | All scripts attached to the same entity |
ContextPolicy::per_script() | All attachments of the same script, i.e. one script on many entities |
ContextPolicy::shared() | All scripts, there is only one context |
Set the policy on the scripting plugin:
app.add_plugins(LuaScriptingPlugin::default().set_context_policy(
ContextPolicy::shared(),
));Sharing a context makes it easy to share data between scripts, at the cost of scripts being able to interfere with each other.
Warning
In a shared context, scripts overwrite each other’s top level functions when loaded. Use registered callbacks so each callback reaches the right script.
A script’s context is busy while one of its callbacks runs, which limits which scripts it can call immediately.
Custom policies
A policy is a list of rules, tried in order until one applies. per_script() could be written as:
let policy = ContextPolicy {
priorities: vec![Arc::new(ContextRule::Script), Arc::new(ContextRule::Shared)],
};Each rule maps the script’s attachment to a ContextKey, and scripts with the same key share a context:
pub struct ContextKey {
pub entity: Option<Entity>,
pub script: Option<AssetId<ScriptAsset>>,
}So the policy reads: if there is a script, the key is just the script. Failing that, ContextRule::Shared always applies, returning the empty key.
For entirely custom rules, implement ContextKeySelector, or pass a closure Fn(&ScriptAttachment) -> Option<ContextKey>.
To change what is in a context, see Customizing Contexts.