# Tween.value() [Tween](https://rustic-game-engine.pages.dev/markdown/api/tween.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 `Tween.value(from, to, timing, onUpdate, easing?)` ## 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 | Parameter | Meaning | | --- | --- | | to / from | Finite scalar, three-component vector or nonzero four-component quaternion matching the property. | | timing | Finite non-negative seconds, or an object with exactly one of duration or positive speed. | | easing | An Ease constant; Linear by default. Options can supply easing. | | onUpdate | Receives each interpolated value for script/UI state. | ## Return and timing Entity and value tweens return an [operation handle](https://rustic-game-engine.pages.dev/markdown/api/operation-handles.md). The engine advances it each scene frame and queues completion during Update. No user Update callback is required. ## 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"); } ``` Receives each interpolated scalar in the sample callback. ### Lua 5.4 ```lua Tween.value(0, 1, 2, function(value) rustic.log("info", "sample received") end, Ease.OutCubic) ``` ### JavaScript ```javascript Tween.value(0, 1, 2, (value) => rustic.log("info", "sample received"), Ease.OutCubic); ``` ### Python ```python Tween.value(0, 1, 2, lambda *args: rustic.log("info", "sample received"), Ease.OutCubic) ``` ### C++ ```cpp Tween::value(0, 1, 2, [](RusticValue value) { rustic.log("info", "sample received"); }, Ease::OutCubic); ``` ### C# ```csharp Tween.value(0, 1, 2, args => rustic.log("info", "sample received"), Ease.OutCubic); ``` ### Luau ```lua Tween.value(0, 1, 2, function(value) rustic.log("info", "sample received") end, Ease.OutCubic) ``` ### C ```c Tween.value((RusticValue){.type=RUSTIC_NUMBER,.number=0}, (RusticValue){.type=RUSTIC_NUMBER,.number=1}, 2, Ease.OutCubic, on_sample, NULL); ``` ### Java ```java Tween.value(0, 1, 2, args -> rustic.log("info", "sample received"), Ease.OutCubic); ``` ### PHP ```php Tween::value(0, 1, 2, fn(...$args) => $rustic->log("info", "sample received"), Ease::OutCubic); ``` ### HTML / inline JS ```javascript Tween.value(0, 1, 2, (value) => rustic.log("info", "sample received"), Ease.OutCubic); ``` ## Shared Tween constraints - The start value is captured on first advancement. Zero duration applies the final value on the next advancing frame. - Speed is units/second, or radians/second for rotation. Easing changes instantaneous velocity; speed-based duration uses the total distance. - Transforms are local to the parent. Opacity and Color are bounded; Fov is in radians between zero and pi on perspective cameras. Arbitrary component reflection is not supported; use value callbacks for your state. - Avoid physics or Update writes to the same property. If multiple actions write it, the last-created action writes last. - 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 - [Tween.to()](https://rustic-game-engine.pages.dev/markdown/api/tween/to.md) - [Tween.move()](https://rustic-game-engine.pages.dev/markdown/api/tween/move.md) - [Tween.rotate()](https://rustic-game-engine.pages.dev/markdown/api/tween/rotate.md) - [Tween.scale()](https://rustic-game-engine.pages.dev/markdown/api/tween/scale.md) [All tween APIs](https://rustic-game-engine.pages.dev/markdown/api/tween.md)