# Smooth.smoothDamp() [Smooth and Interpolation](https://rustic-game-engine.pages.dev/markdown/api/smooth.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 `Smooth.smoothDamp(current, target, velocity, smoothTime, delta)` ## 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 Lerp accepts scalars or three-component vectors. Slerp accepts nonzero [x, y, z, w] quaternions. Progress and inputs must be finite. Easing defaults to Linear. SmoothDamp takes scalar state, a smoothing time and elapsed seconds; feed the returned velocity into the next call. ## Return and timing Math results are synchronous. JavaScript smoothDamp returns {value, velocity}; native return shapes differ (for example C# tuple and Java double[2]). Interpolation aliases Smooth in Lua, Luau, JavaScript, Python, C, C++, PHP and HTML inline JavaScript. C# and Java expose these functions through Smooth. ## 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 result = Smooth.smoothDamp(0, 10, 0, 0.5, 0.016) ``` ### JavaScript ```javascript const result = Smooth.smoothDamp(0, 10, 0, 0.5, 0.016); ``` ### Python ```python result = Smooth.smoothDamp(0, 10, 0, 0.5, 0.016) ``` ### C++ ```cpp auto result = Smooth::smoothDamp(0, 10, 0, 0.5, 0.016); ``` ### C# ```csharp var result = Smooth.smoothDamp(0, 10, 0, 0.5, 0.016); ``` ### Luau ```lua local result = Smooth.smoothDamp(0, 10, 0, 0.5, 0.016) ``` ### C ```c RusticDamping result = Smooth.smoothDamp(0, 10, 0, 0.5, 0.016); ``` ### Java ```java var result = Smooth.smoothDamp(0, 10, 0, 0.5, 0.016); ``` ### PHP ```php $result = Smooth::smoothDamp(0, 10, 0, 0.5, 0.016); ``` ### HTML / inline JS ```javascript const result = Smooth.smoothDamp(0, 10, 0, 0.5, 0.016); ``` ## Shared Smooth and Interpolation constraints - This example prints interpolated values immediately in Start; it creates no operation handle. - InverseLerp and remap do not clamp out-of-range values. A degenerate input interval returns inverse progress zero (and remap returns outMin). Damping uses an analytic spring rather than a fixed per-frame fraction. - Use Tween.value or Animation.value when you want the engine to advance interpolation and dispatch callbacks over time. - 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 - [Smooth.lerp()](https://rustic-game-engine.pages.dev/markdown/api/smooth/lerp.md) - [Smooth.slerp()](https://rustic-game-engine.pages.dev/markdown/api/smooth/slerp.md) - [Smooth.inverseLerp()](https://rustic-game-engine.pages.dev/markdown/api/smooth/inverse-lerp.md) - [Smooth.remap()](https://rustic-game-engine.pages.dev/markdown/api/smooth/remap.md) [All smooth APIs](https://rustic-game-engine.pages.dev/markdown/api/smooth.md)