# Events.connect() [Events and signals](https://rustic-game-engine.pages.dev/markdown/api/events.md) ## Compatibility **Supported languages:** C, C++, C#, Python, JavaScript, Lua 5.4, Luau, Java, PHP and HTML/inline JavaScript (binding spellings and return shapes differ). Use a compatible native engine build and the language tools required by your binding. This does not establish browser/mobile export or release qualification for every OS. The signature below is the shared reference notation; language examples show the actual binding syntax. Question marks mark optional arguments and explicit defaults are shown where recorded. Do not copy reference notation as a typed declaration. See [Feature status and compatibility](https://rustic-game-engine.pages.dev/markdown/reference/compatibility.md) for API 1.0/1.1 and per-method restrictions. Engine release tags and Docs v0.1 are independent versions. ## Signature `Events.connect(entity, name, callback)` ## Setup and usage These engine-owned services work in Lua 5.4, Luau, JavaScript, Python, C, C++, C#, Java, PHP, and HTML inline JavaScript. Follow [Use gameplay actions](https://rustic-game-engine.pages.dev/markdown/guides/gameplay-actions.md) to create and attach a script, install external toolchains, and choose the correct language binding. PHP and HTML scripts belong under `ui/`; CSS alone runs no gameplay code. The Calls section uses JavaScript signatures. The function examples below include native syntax for all ten script types, including SDK-specific alternatives and limitations. Attach a JavaScript Object Component script to the specified target and press **Play**. Globals are supplied by the engine. Schedule actions from `Start` or a callback, rather than at script top level. Native languages use typed options and their own builder conventions; see the guide's language bindings. ## Parameters Name is the exact signal name. Callback receives payload arguments. Source is an optional stable entity ID or resolvable scene path. Payload supports booleans, finite numbers, strings/IDs, vectors and quaternions, not arbitrary nested objects. ## Return and timing On/once/connect return a connection with disconnect. Emit queues delivery during Update before the user frame callback; it never synchronously enters another language runtime. ## Execution behavior Core write timing differs between immediate Lua host calls, deferred JavaScript/Web commands and external SDK query flushes. Scheduled actions advance with the scene clock; synchronous queries evaluate at the call. Follow [execution rules](https://rustic-game-engine.pages.dev/markdown/guides/scripting.md#when-mutations-take-effect) and the return/timing notes for this category. ## Language examples Choose one snippet at a time and place it inside your language's Start/on_start callback. These are independent examples; each creates its own handles or builders. Follow [Gameplay language bindings](https://rustic-game-engine.pages.dev/markdown/guides/gameplay-actions/language-bindings.md) for imports and callback registration. Python must import the modules used in its snippet from rustic; C# uses using static Rustic; Java examples belong inside a Rustic subclass; PHP callbacks declare global $rustic. HTML snippets go inside an inline script in a ui/ HTML asset. Use an anchored Part for transform and effect examples, an unanchored collidable Part for forces, and a perspective camera named Camera for camera examples. Create Target for follow examples. Audio examples require assets/music.ogg in the Play snapshot. Replace scene paths with those listed by Game.scene.List(). Animation playback and sequence-animation examples require the Reveal fixture on the [Animation page](https://rustic-game-engine.pages.dev/markdown/api/animation.md); marker callbacks also require its Halfway marker. Run clock controls separately; a paused clock cannot advance a timer. C callback examples use these file-scope functions before on_start: ```c static void on_done(void) { rustic.log("info", "done"); } static void on_sample(RusticValue value) { (void)value; rustic.log("info", "sample received"); } static void on_event(const RusticValue *args, size_t count) { (void)args; (void)count; rustic.log("info", "event received"); } ``` ### Lua 5.4 ```lua local connection = Events.connect(rustic.entity_id(), "DoorOpened", function(...) rustic.log("info", "event received") end) ``` ### JavaScript ```javascript const connection = Events.connect(rustic.entity_id(), "DoorOpened", (...args) => rustic.log("info", "event received")); ``` ### Python ```python connection = Events.connect(rustic.entity_id(), "DoorOpened", lambda *args: rustic.log("info", "event received")) ``` ### C++ ```cpp auto connection = Events::connect(rustic.entity_id(), "DoorOpened", [](const RusticValue::Array& args) { rustic.log("info", "event received"); }); ``` ### C# ```csharp var connection = Events.connect(rustic.entity_id(), "DoorOpened", args => rustic.log("info", "event received")); ``` ### Luau ```lua local connection = Events.connect(rustic.entity_id(), "DoorOpened", function(...) rustic.log("info", "event received") end) ``` ### C ```c RusticConnection connection = Events.connect(rustic.entity_id(), "DoorOpened", on_event, false); ``` ### Java ```java var connection = Events.connect(rustic.entity_id(), "DoorOpened", args -> rustic.log("info", "event received")); ``` ### PHP ```php $connection = Events::connect($rustic->entity_id(), "DoorOpened", fn(...$args) => $rustic->log("info", "event received")); ``` ### HTML / inline JS ```javascript const connection = Events.connect(rustic.entity_id(), "DoorOpened", (...args) => rustic.log("info", "event received")); ``` ## Shared Events and signals constraints - Global on/once subscriptions are distinct from object signals. For an object signal use connect(object, name, callback) and emit(name, args, object). - Language instances in the same play scene can communicate; no network or inter-scene transport is implied. - Payload limits are 64 arguments, 4096 bytes per string and 16 KiB combined. The scene retains at most 4096 subscriptions and 4096 callbacks per queue. - Destroying an object removes its scoped connections. Unrelated object destruction does not remove a global script subscription. - Check script attachment, enabled state and the Console when an operation fails. Asynchronous errors also appear in operation state. Callback exceptions disable the owner and clean up its actions. - Owner destruction, disable, successful reload or Stop cleans up owned actions and subscriptions. Failed reload retains the previous behavior's operations. See [Operation handles](https://rustic-game-engine.pages.dev/markdown/api/operation-handles.md) for controls and lifetime details. ## Errors and debugging Read the constraints above and the Console diagnostic. Invalid types, non-finite values, stale targets or unavailable native services can fail validation. A failed callback disables the behavior; a failed source reload keeps the last good instance. Exact error messages depend on the language adapter. See [Troubleshooting](https://rustic-game-engine.pages.dev/markdown/troubleshooting.md). ## Related APIs - [Events.on()](https://rustic-game-engine.pages.dev/markdown/api/events/on.md) - [Events.once()](https://rustic-game-engine.pages.dev/markdown/api/events/once.md) - [Events.emit()](https://rustic-game-engine.pages.dev/markdown/api/events/emit.md) - [connection.disconnect()](https://rustic-game-engine.pages.dev/markdown/api/events/connection-disconnect.md) - [Events.disconnect()](https://rustic-game-engine.pages.dev/markdown/api/events/disconnect.md) [All events APIs](https://rustic-game-engine.pages.dev/markdown/api/events.md)