# Chain Chains move components along spline paths or simulation paths for material handling systems, tool changers, and other applications requiring continuous linear motion. {% hint style="info" %} **New Feature**: Burst Compiler optimization was added in realvirtual **6.0.9** (beta) providing 20-33x performance improvements for chain simulations. {% endhint %} ## Overview Chains provide continuous movement of multiple components along a defined path. This is useful for modeling material handling systems or tool changers that are driven by chains. They are always connected to a Drive component that controls the chain's movement speed and position. Chain elements are automatically created and positioned along the spline during simulation. {% hint style="info" %} Chains work with both custom splines and Unity Splines. We recommend using Unity Splines for better editor integration and visual feedback. {% endhint %} {% hint style="warning" %} Simulation path functionality requires realvirtual Simulation, which is not included in the base realvirtual package. There are separate demos for this in realvirtual Simulation. {% endhint %} You can find a demo scene at `Assets/realvirtual/Scenes/DemoChain` demonstrating chain functionality. ### Basic Concepts A chain is always connected to a drive, so the movement of the chain depends on the current drive position and speed. Usually, you should use a Drive with the Axis set to Virtual to move the chain. One or several Chain Elements are connected to the chain. These Chain Elements are created automatically upon simulation start by the chain. Usually, these chain elements should be Prefabs within your project. The Chain script requires a Spline script to be attached to the same component. The spline script defines the exact path of the chain based on points with in and out tangents. ## Properties ### Settings #### Chain Orientation Determines whether the chain moves horizontally or vertically. * **Type**: Enum (Horizontal, Vertical) * **Default**: Horizontal * **Use case**: Set based on your mechanical system orientation #### Chain Element Prefab used for individual chain elements along the spline. * **Type**: GameObject reference * **Default**: None * **Use case**: Assign your custom chain link or carrier prefab #### Connected Drive Drive component that controls chain movement. * **Type**: Drive reference * **Default**: None * **Use case**: Connect to a Drive with Virtual axis for chain control #### Number of Elements Total number of chain elements created along the spline. * **Type**: Integer * **Default**: 10 * **Range**: 1 to 1000 * **Use case**: Adjust based on spline length and element spacing needs #### Start Position Offset position along the spline where the first element is placed. * **Type**: Float * **Default**: 0 * **Range**: 0 to spline length * **Use case**: Adjust starting position for alignment with mechanical systems #### Calculate Delta Position Automatically calculates spacing between chain elements. * **Type**: Boolean * **Default**: true * **Use case**: Enable for even distribution, disable for custom spacing #### Scaled On Fixed Length Maintains constant total spline length for external drive positioning. * **Type**: Boolean * **Default**: false * **Use case**: Enable when external drives provide positional data for elements ## Performance Optimization ### Burst Compiler Optimization {% hint style="info" %} This feature was added in realvirtual **6.0.9** (beta) {% endhint %} The Chain component supports Unity's Burst Compiler for dramatically improved performance when simulating large numbers of chain elements. This optimization uses SIMD (Single Instruction, Multiple Data) compilation to native code, providing: **Performance Benchmarks:** * **Kinematic elements** (MoveRigidBody=false): **29-33x speedup** * **Physics elements** (MoveRigidBody=true): **19-23x speedup** #### How It Works Burst optimization operates in two modes depending on your chain element configuration: **Kinematic Mode (Maximum Performance)** * Uses Unity's TransformAccessArray for parallel batch processing * Ideal for visual chain elements without physics interactions * Achieves 29-33x performance improvement * Set **MoveRigidBody=false** on ChainElements to use this mode **Physics Mode (High Performance)** * Uses traditional Rigidbody updates with Burst-compiled calculations * Required when chain elements need collider interactions * Achieves 19-23x performance improvement * Set **MoveRigidBody=true** on ChainElements for physics #### Setup Instructions **One-Click Setup (Recommended)** If Burst optimization is not enabled, you'll see a warning message in the Chain Inspector with performance information and a setup button.

Chain Inspector showing Burst optimization not enabled with one-click setup button

1. Click **Enable Burst Optimization (Install Package & Define)** button in the Chain Inspector 2. Unity will automatically: * Install the Burst Compiler package * Add `REALVIRTUAL_BURST` to Script Compilation Symbols * Recompile scripts with Burst optimization enabled 3. Restart Unity if prompted **Manual Setup** 1. Install Unity Burst Compiler package via Package Manager 2. Add `REALVIRTUAL_BURST` to **Project Settings > Player > Script Compilation Symbols** 3. Unity will automatically recompile with Burst optimization **After Setup** Once enabled, the Chain Inspector displays confirmation of active optimization:

Chain Inspector with Burst optimization enabled showing performance tips

#### Optimizing Chain Elements For maximum performance, configure your ChainElements based on their purpose: **Visual-Only Elements (Fastest)** * Set **MoveRigidBody=false** on the ChainElement component * Use for chain links, carriers, or fixtures that don't need physics * Achieves 29-33x speedup with kinematic batch processing **Physics-Interactive Elements** * Set **MoveRigidBody=true** on the ChainElement component * Required for elements with colliders that interact with other objects * Still achieves 19-23x speedup with Burst-optimized physics updates

ChainElement Inspector showing MoveRigidBody property with performance guidance

The ChainElement Inspector provides inline performance tips to help you choose the right setting. #### Advanced Settings **Spline Bake Resolution** * Controls the number of pre-calculated spline samples used by Burst jobs * Higher values = smoother interpolation but more memory usage * Default: 100 samples * Adjust based on spline complexity and available memory **Use Burst Optimization** * Enable/disable Burst processing at runtime * Defaults to enabled when REALVIRTUAL\_BURST is defined * Useful for performance comparisons or debugging #### Common Use Cases **High-Speed Bucket Elevators** * Set MoveRigidBody=false on buckets for 29-33x speedup * Buckets follow path without physics interaction * Ideal for material transport visualization **Overhead Conveyors with Load Detection** * Set MoveRigidBody=true on carriers for physics-based load pickup * Still achieves 19-23x speedup while maintaining collision detection * Necessary when carriers interact with sensors or parts **Mixed Configuration** * Combine kinematic and physics elements in the same chain * Use physics only where needed (e.g., pickup/drop zones) * Optimize performance while maintaining required functionality #### Technical Details Burst optimization works by: 1. Pre-calculating spline positions and tangents into native arrays 2. Batch-processing all element position updates in parallel 3. Using SIMD instructions for vectorized calculations 4. Minimizing managed-to-native transitions The system automatically handles: * Spline position interpolation * Tangent calculation for element orientation * Batch updates synchronized with drive events * Memory management for native arrays ## Usage Examples ### Basic Chain Setup 1. Create a spline path using Unity Splines or custom spline 2. Add **Chain** component to the spline GameObject 3. Add **ChainUnitySpline** component for Unity Splines integration 4. Assign **Chain Element** prefab 5. Connect to a **Drive** component with Virtual axis 6. Set **Number of Elements** based on your requirements ### Unity Splines Integration We recommend using Unity Splines for the chain. To do so, the Unity Splines package must be installed. Once the Unity Splines package is installed, the chain can be defined as follows: 1. In **Project Settings > Player**, add `REALVIRTUAL_SPLINES` under Script Compilation Symbols to use Unity Splines with realvirtual chains 2. Right-click in the Hierarchy and select the desired base spline from the **Spline** menu 3. Unity provides a Spline editing mode in the Scene view for adjusting spline control points. For each spline control point, Unity also shows the up direction at the point (red arrow). This is relevant if you want to set up a vertical chain 4. Add the **ChainUnitySpline** and **Chain** components to the created GameObject Once the chain is set up, it can be used with ChainElements and drives. ### Vertical Chain Configuration To construct a vertical chain, follow these steps: 1. Build the spline in the positive Z direction, starting from the bottom-right anchor point, and continue clockwise 2. Maintain a vertical angle of exactly 90 degrees. Avoid inclinations to prevent misalignment with interpolated curves representing the height difference 3. Note that these instructions are currently applicable only to splines with four anchor points and not more 4. Ensure that the front of the chain element also faces in the positive Z direction. This orientation is necessary for the parent GameObject 5. Set **Chain Orientation** to Vertical > **💡 Hint**\ > For vertical chains, use exactly four anchor points and maintain precise 90-degree angles to prevent misalignment with interpolated curves. ## Editor Tools ### Spline Construction For extending a spline or creating a first point, you can click the **Extend** button on the Spline. This generates a Point with 2 included Tangent points. You can move these points like any GameObject to construct your spline. The order of these GameObjects also defines the order of the points in the spline. If you select **Loop**, the spline is closed and the last point is connected to the first point of the spline. ### Unity Splines Editor * Visual spline editing in Scene view * Control point manipulation with handles * Up direction indicators (red arrows) for vertical chain setup * Real-time spline preview and adjustment ## See Also * [Chain Element](https://doc.realvirtual.io/components-and-scripts/motion/chain-element) - Individual elements moving along the chain * [Drive](https://doc.realvirtual.io/components-and-scripts/motion/drive) - Motor control for chain movement * [Spline documentation](https://docs.unity3d.com/Packages/com.unity.splines@latest) - Unity Splines package reference *** © 2025 realvirtual GmbH [https://realvirtual.io](https://realvirtual.io/) - All rights reserved. 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