# Animation.transition() [Animation](https://rustic-game-engine.pages.dev/markdown/api/animation.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 `Animation.transition(entity, fromClip, toClip, options?)` ## 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 | | --- | --- | | clip | Object with name, positive duration, tracks and optional markers. A track contains target and keys. | | keys | At least two time/value entries beginning at zero with strictly increasing times; a starting key's easing controls the following interval. | | play options | speed (default 1), loop, blendIn/Out (seconds), blendInEase/OutEase, weight (default 1), additive, mask, layered, progressionEase. | | blend options | duration (default 0.3 seconds) and easing for the transition, plus playback options. | | marker | Source-clock time and event name; add before starting playback. | | IK options | pole, weight, duration and easing; joints must form a direct root/middle/tip parent chain. | ## Return and timing Clips lists registered names; load/register/addMarker update the engine registry. Play returns a handle with stop, speed, loop and onMarker in addition to standard controls. Value and procedural actions return operation handles; value callbacks receive the interpolated scalar/vector/quaternion. ## 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 $rustic. HTML snippets go inside an inline script in a ui/ HTML asset. Use an anchored Part for transform and effect examples, an unanchored collidable Part for forces, and a perspective camera named Camera for camera examples. Create Target for follow examples. Audio examples require assets/music.ogg in the Play snapshot. Replace scene paths with those listed by Game.scene.List(). Animation playback and sequence-animation examples require the Reveal fixture on the [Animation page](https://rustic-game-engine.pages.dev/markdown/api/animation.md); marker callbacks also require its Halfway marker. Run clock controls separately; a paused clock cannot advance a timer. C callback examples use these file-scope functions before on_start: ```c static void on_done(void) { rustic.log("info", "done"); } static void on_sample(RusticValue value) { (void)value; rustic.log("info", "sample received"); } static void on_event(const RusticValue *args, size_t count) { (void)args; (void)count; rustic.log("info", "event received"); } ``` This minimal example blends two instances of Reveal. Replace the names with two registered clips for a pose change. ### Lua 5.4 ```lua Animation.transition(rustic.entity_id(), "Reveal", "Reveal") ``` ### JavaScript ```javascript Animation.transition(rustic.entity_id(), "Reveal", "Reveal"); ``` ### Python ```python Animation.transition(rustic.entity_id(), "Reveal", "Reveal") ``` ### C++ ```cpp Animation::transition(rustic.entity_id(), "Reveal", "Reveal", 0.3, Ease::OutCubic); ``` ### C# ```csharp Animation.transition(rustic.entity_id(), "Reveal", "Reveal", 0.3, Ease.OutCubic); ``` ### Luau ```lua Animation.transition(rustic.entity_id(), "Reveal", "Reveal") ``` ### C ```c Animation.transition(rustic.entity_id(), "Reveal", "Reveal", 0.3, Ease.OutCubic, NULL); ``` ### Java ```java Animation.transition(rustic.entity_id(), "Reveal", "Reveal", 0.3, Ease.OutCubic); ``` ### PHP ```php Animation::transition($rustic->entity_id(), "Reveal", "Reveal"); ``` ### HTML / inline JS ```javascript Animation.transition(rustic.entity_id(), "Reveal", "Reveal"); ``` ## Shared Animation constraints - Import glTF/GLB/FBX through Explorer and attach to the mesh entity to play skeletal clips. Source node_N descendants, inverse binds, skin weights and named clips are bound before Start. Use clips to discover actual names. Explicit load requires a fresh target. - Tracks target Position, Rotation, Scale, Color, Opacity, Fov or child/path/Property. C/C++ use registerClip; native facades use typed clip/key/marker records. - Source time is linear at selected speed unless progressionEase warps sampling. Markers use raw source time; running actions retain their clip snapshot. Blend duration stays in scene seconds when speed changes. - Blend/transition samples both source and destination clips. Start a base clip before a masked layer; masks match track names or hierarchy prefixes. Additive tracks apply a delta from their initial pose. - Turning loop off finishes the current cycle. Stop cancels without resetting the pose; completion retains the final pose unless blend-out restores the base. - IK solves in world space, preserves segment lengths and clamps unreachable targets. FootPlacement aliases IK; headTracking is finite lookAt, requiring controller updates for changing targets. - Clip limits are 4096 tracks, one million keys and 4096 markers. Add markers before playback because running actions retain their clip snapshots. - glTF retains linear/step/cubic-spline interpolation; FBX is baked at 60 Hz. Live renderer skinning uses four linear influences. Morph targets, dual-quaternion skinning and animation graph/editor UI are not implemented. - 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 - [Animation.clips()](https://rustic-game-engine.pages.dev/markdown/api/animation/clips.md) - [Animation.load()](https://rustic-game-engine.pages.dev/markdown/api/animation/load.md) - [Animation.register()](https://rustic-game-engine.pages.dev/markdown/api/animation/register.md) - [Animation.addMarker()](https://rustic-game-engine.pages.dev/markdown/api/animation/add-marker.md) - [Animation.play()](https://rustic-game-engine.pages.dev/markdown/api/animation/play.md) [All animation APIs](https://rustic-game-engine.pages.dev/markdown/api/animation.md)