**Rope Toolkit** version 2.2.3 The Rope Toolkit brings *stable* and *fast* rope physics to your project. The rope component can be used to simulate simple wires or more advanced setups with pulleys and weights that require active collision detection. The bundled example scenes show how to connect the rope up to simulate cranes, rope bridges, swings and a boxing ring. The rope component is written with performance in mind and many compute intensive tasks are handled by [Unity jobs on separate threads accelerated using the Burst compiler](https://unity.com/dots). As a result, the toolkit has excellent performance on mobile devices. Overview ======== (##) Features * Stable & fast rope physics * Mobile friendly! * Many tweakable user parameters * Ability to dynamically split ropes using the SplitAt() method * 4 different rope connection types allow interaction with the rest of the scene - Pin Rope To Transform - Pin Transform To Rope - Pull Rigidbody To Rope - Two Way Coupling Between Rigidbody And Rope * Scene view handles for adjusting rope spawn curve * High performance is achieved using Unity jobs and the Burst compiler - Typical performance for the example scene with collisions enabled: - ~0.2 ms spent in job threads - ~0.7 ms spent on the main thread - Typical performance for the example scene with collisions disabled: - ~0.15 ms spent in job threads - ~0.35 ms spent on the main thread * Full source code * Example scenes - Main - Shows how ropes and rigidbodies can be connected together in a typical scene - Use the mouse to interact with the rope and the Space key to split ropes being interacted with - DynamicAttach - Shows how to attach and detach ropes using the scripts - BoxingRing - Shows how ropes and rigidbodies can influence each other through collisions (##) Current Limitations * Collision support for convex Mesh, Box, Sphere and Capsule colliders only * Scripting knowledge required for advanced rope interactions Requirements ============ * Burst 1.1.2 or above Components ========== (##) Rope This is the main component that simulates and renders the rope (##) RopeConnection This component connects the rope it is attached to to a transform or rigidbody component in the scene. The resulting behaviour depends on what type of connection is used: Pin Rope To Transform : Pins a point on the rope to a point on a transform. The transform can move freely and the rope will always follow along. Pin Transform To Rope : Pins a point on a transform to a point on the rope. The rope will move freely and the transform will always follow along. This connection takes control of the transform. Pull Rigidbody To Rope : Pulls a point on a rigidbody towards a point on the rope by applying velocity changes to the rigidbody. This connection does not take control of the rigidbody, other forces and constraints are respected. Two Way Coupling Between Rigidbody And Rope : Introduces a two-way coupling between the rope and a rigidbody. The rope will react to the rigidbody and feedback impulses back to the rigidbody allowing for complicated setups such as the crane in the example scene. Care must be taken so that the rope `mass per meter` value is comparable to the masses of connected rigidbodies, otherwise the simulation may blow up. This connection does not take control of the rigidbody, other forces and constraints are respected. Instructions ============ (##) First time use in a new project The **Rope Toolkit requires the Burst package (by Unity) to function properly**. Make sure to import it using the Package Manager before importing the Rope Toolkit into your project. Follow these steps to import the Burst package: 1. Choose `Window -> Package Manager` from the menu bar 2. In the window that appears, select `Unity Registry` from the drop-down menu next to the `+` sign 3. In the list to the left, select the `Burst` package and press `Install` in the lower right corner 4. The Rope Toolkit can be found in the `My Assets` drop-down menu of the Package Manager (instead of `Unity Registry` in step 2). Import it in the same way as the Burst package. (##) Workflow 1. Create an empty game object 2. Attach the Rope script to it 3. Add a few spawn points either using the scene view buttons (`Push spawn point`, `Pop spawn point`) or by manually changing the `Spawn Points` property in the inspector 4. Move around the spawn points using the scene view handles - Hold down left `Shift` to switch to the ordinary transform tool for more fine-grained control 5. Assign a material to the `Material` property of the rope - Optionally adjust the `Tiling` of the material - 1 scene unit is mapped to 1 texture tile (x-axis) lengt-wise - 1 texture tile (y-axis) wraps around the rope curlwise 6. Optionally attach any number of `RopeConnection` components to the rope - Set the `Body` or `Transform` reference to the object the rope should be connected to - Set the `Local Connection Point` to be the point in object local space to which the rope should be attached (##) General tips * Examine the example scenes to get an understanding for how to connect the rope in a typical scene * Change the tweakable parameters when in play-mode to get a feel for what they do * There are tooltips for all tweakable parameters * Look at the helper scripts to get an understanding for how one can interact with the rope using custom scripts (##) Performance tips * Avoid enabling collisions unless absolutely necessary * Disable simulation of ropes that are far away or out of view using a custom script (they will still be rendered) * Only call rope methods in a custom script from `FixedUpdate()` or `LateUpdate()` (##) Collisions Collision detection is very performance intensive, as all physics queries have to be performed on the main thread. Aim to keep the `Stride` value as high as possible to reduce the amount of queries. Another approach is to disable simulation of ropes that require collisions more aggressively and keep the number of active ropes with collisions enabled to a bare minimum, even though the total number in the scene is high. (##) Stiffness Rope stiffness depends on many factors: the `Stiffness` value of the rope, the `Resolution` of the rope, the `Substeps` and `Solver Iterations` of the rope and finally the `Fixed Timestep` value in `Project Settings` -> `Time`. To achieve a stiff rope, choose a high stiffness value, a low resolution value, many substeps and solver iterations and a low fixed time step. Scripting interface =================== The rope is simuated using a set of inter-connected particles (visuaized by spheres when selecting a rope in edit-mode). Since the physics simulation is inherently stable, one can move around these particles in almost any way imaginable. This enables many custom setups such as the rope bridge in the example scene (see `RopeBridgePlank.cs`). (##) Interface To fascilitate custom interactions with ropes, the rope component exposes a small scripting interface. The table below shows the properties and methods available. For more information on a particular property or method, see the description in the source file. `measurements` : Returns the measurements of the rope. The measurements remain constant after the rope is first initialized. `currentBounds` : The current world-space bounds of the visual mesh `PushSpawnPoint()` : Adds a new spawn point to the rope. May be called from edit-mode. `PopSpawnPoint()` : Removes the last spawn point of the rope. May be called from edit-mode. `GetParticleIndexAt(distance)` : Returns the index of the simulation particle at a particular distance along the curve of the rope `GetScalarDistanceAt(particleIndex)` : Returns the scalar distance along the curve of the rope that a particular simulation particle is located at. The scalar distance is a value between 0 and 1. The lengthMultiplier is not taken into account. To get the distance along the rope in world space, multiply the scalar distance by the realCurveLength measurement. `GetPositionAt(particleIndex)` : Returns the current position of a particular simulation particle `SetPositionAt(particleIndex, position)` : Sets the position of a particular simulation particle `SetPositionAt(particleIndex, position, maxImpulseStrength)` : Sets the position of a particular simulation particle while at the same time making sure not to apply a larger impulse than the specified max impulse strength. If the max impulse strength is exceeded, the particle will be moved part-way towards the target position. This method is useful when limiting the strength of helper scripts that interact with the rope. `GetVelocityAt(particleIndex)` : Returns the current velocity of a particular simulation particle `SetVelocityAt(particleIndex, velocity)` : Sets the velocity of a particular simulation particle `GetMassMultiplierAt(particleIndex)` : Returns the mass multiplier of a particular simulation particle. This value can be used to increase or decrease a particle's influence on neighboring particles. A value of 0 will make the particle immovable. A value of 2 will make the particle twice as heavy as its neighbors. The default value is 1. `SetMassMultiplierAt(particleIndex, value)` : Sets the mass multiplier of a particular simulation particle. This value can be used to increase or decrease a particle's influence on neighboring particles. A value of 0 will make the particle immovable. A value of 2 will make the particle twice as heavy as its neighbors. The default value is 1. `GetClosestParticle(point, out particleIndex, out distance)` : Finds the simulation particle closest to a particular point `GetClosestParticle(ray, out particleIndex, out distance, out distanceAlongRay)` : Finds the simulation particle closest to a particular ray `RegisterRigidbodyConnection(particleIndex, rigidbody, rigidbodyDamping, pointOnBody, stiffness)` : Registers a rigidbody connection for the next simulation frame. A rigidbody connection is a two-way coupling of a simulation particle to a traditional rigidbody. Make sure to call this method from FixedUpdate(). Any simulation particle involved in a rigidbody connection will get its mass multiplier reset to 1 at the end of the simulation frame. `ResetToSpawnCurve()` : Resets the rope to its original shape relative to the current transform. Useful when activating a pooled game object that is deactivated and re-activated instead of destroyed and instantiated. `GetCurrentLength()` : Computes the current length of the rope. In contrast to the measurements.realCurveLength field, this value includes the stretching of the rope due to stress. `SplitAt(particleIndex, outNewRopes)` : Splits the rope at a specific simulation particle and returns the rope components of the newly instantiated game objects. Make sure that the supplied array has exactly 2 slots. A Unity message 'OnRopeSplit(Rope.OnSplitParams)' will be sent to each newly created rope. (##) Execution order Make sure the custom script runs before the custom execution order of `Rope.cs`, which defaults to 100. Calling rope methods from `Update()` or after the rope's `FixedUpdate()` will halt the main thread as it waits for the rope simulation jobs to complete. This destroys parallelism and performance. (##) Example usage ```c# using RopeToolkit; public class RopeMover : MonoBehaviour { public Rope rope; public void FixedUpdate() { if (rope == null) { return; } rope.SetMassMultiplierAt(0, 0.0f); // makes particle 0 immovable with respect to the simulation rope.SetPositionAt(0, transform.position); } } ``` FAQ === Q: Why does a rigidbody with [a freeze rotation constraint](https://docs.unity3d.com/ScriptReference/Rigidbody-constraints.html) act strange when it is connected to a rope? : A: This is caused by [a bug in Unity](https://fogbugz.unity3d.com/default.asp?1342781_6lnk429ujeergaf6). Change log ========== (##) v2.2.3 * Introduce a "max impulse strength" parameter to SetPositionAt() enabling an easy way to limit the pull strength of helper scripts (such as in the RopeMouseInteraction script) (##) v2.2.2 * Fix bug where rope length was not preserved accurately when splitting the rope using SplitAt() (##) v2.2.1 * Use game object layer for rendering * Add shadow casting mode * Add setting for using a custom gravity value or the global physics gravity - **[ACTION REQUIRED]** Update any rope component that has the simulation.gravity property set to use the new simulation.useCustomGravity and simulation.customGravity properties instead * Move custom mesh settings into their own category - **[ACTION REQUIRED]** Update any rope component that uses a custom mesh to use the new customMesh category instead * Add custom mesh scale override * Add ability to stretch custom meshes instead of them moving too far apart when the rope is stretched (##) v2.2.0 * Rename package from "Rope Minikit" to "Rope Toolkit" to reflect its fully featured state - **[ACTION REQURED]** Any custom scripts must now reference the namespace `RopeToolkit` * Add support for simulation substeps to enable stiffer ropes - **[ACTION REQURED]** To not have to retweak rope properties in an existing project, set the simulation substeps property (found under `Rope/Simulation/Advanced`) to `1` after importing the new version of the toolkit * Add ability for ropes to influence rigidbodies when collisions are enabled - See the `Rope/Collisions/Influence Rigidbodies` property * Add BoxingRing example scene to show how ropes can now push rigidbodies away * Remove ability to move one end of a rope by updating its Transform component - use the RopeConnection component instead - This introduced subtle bugs in certain situations * Reorganize rope inspector view slightly (##) v2.1.0 * Add interpolation property that may be used to smooth the motion of the rope - This is especially useful when a low fixed update rate is used - The behavior mimics the [RigidbodyInterpolation](https://docs.unity3d.com/ScriptReference/RigidbodyInterpolation.html) setting and has the following values - None - Interpolate - Extrapolate * Improve performance when generating rope geometry (by taking advantage of newer Unity APIs) (##) v2.0.0 * Replace the RopePin and RopeRigidbodyConnection components with a single RopeConnection component and add 2 new connection types - There are now 4 connection types: - Pin Rope To Transform - Pin Transform To Rope - Pull Rigidbody To Rope - Two Way Coupling Between Rigidbody And Rope - Warning: This change breaks backwards compatibility! * Add gravity property for setting the gravity vector on a per-rope basis * Fix bug where wrong impulse function was used for rigidbody feedback - Warning: This might require re-tweaking of the stiffness/damping values of your existing rope setups * Fix bug where rigidbody rotational constraints would not be handled properly when connected to a rope * Reskin example scene * Switch to 3 digit semantic versioning (##) v1.11 * More accurate rope length calculation on SplitAt() * Fix bug where multiple ropes with custom meshes would allocate unnecessary memory (##) v1.1 * Add support for dynamically splitting the rope using the new SplitAt() method - Try it out in the example scene by grabbing a rope with the mouse pointer and pressing space before letting go! * Add support for custom meshes that can be rendered instead of the default rope cylinder - To illustrate this, the crane in the example scene now has a chain with links instead of a smooth rope * Change RopePin and RopeRigidbodyConnection components to be lazily initialized * Rename RopeMeasurements struct to Measurements and make it a sub-type of Rope * Fix bug where toggling the simulation.enabled flag could result in an IndexOutOfBounds exception (##) v1.03 * Fix bug where one end of the rope could be moved if it collided with something even though it was pinned down using a RopePin component * Fix bug where one end of the rope would show more sag than the other end when the rope was being stretched * Add Rope.GetCurrentLength() method * The example scene rope material now uses an explicit texture as the built-in one previously used caused iOS builds to fail (##) v1.02 * Add soft backdrop to example scene (##) v1.01 * Fix rope enable/disable logic * Add ResetToSpawnCurve() method (##) v1.0 * Initial release Contact ======= Please let me know if you run into any problems when using the toolkit or if you have feedback on how I can improve it in the future. I am also interested in seeing projects that use any of my toolkits in practice! Website: https://gustavolsson.com/ Contact: https://gustavolsson.com/contact/ Copyright 2025 Gustav Olsson