How to open the project

1. Install Unity version 6000.0.23f1
2. Open this repository as a Unity Project

How to run a demo scene

1. In the opened Unity project, you can find three pre-arranged demo-scenes under Project > Assets > Scenes
2. To run any of those in the editor, you can just open it with a double click and then press the play button in the Unity editor. However, for better performance, you might want to build a standalone application, which you can do under File > Build Profiles, where you can select the scene you want to build, as well as other building options. When you are finished, you can press Build and Run

What to do, if the performance is bad?

You can trade off performance for accuracy by changing the Simulation Loop Substeps attribute (which controls the number of subloop iterations of the XPBD algorithm) of the Solver Script attached to the Solver GameObject located in the Hierarchy view. Note that the DemoScene and the LiveDemoScene run with more than 60 FPS in realtime on one of our PCs and the SampleScene runs with 20-50 FPS. The DemoScene in particular is the one we showed live at the presentation, so it should even run in realtime on a laptop.

Another thing you can try to improve performance is to change the timescale under Edit > Project Settings > Time to something smaller than 1.

What parts of the project were done by us?

• We wrote all of the Scripts contained in Project > Assets > Scripts ourselves, except for the FreeFlyCamera.cs as well as the NormalSolver.cs, but the latter one we optimized to reduce garbage collection.
• We designed all scenes (Project > Assets > Scenes) and their UI.
• We modeled the SimpleBalloon.fbx mesh ourselves using Blender.

Codebase structure

The main loop of the XPBD algorithm is contained in Solver.cs. It has references to all the objects being simulated (e.g. ClothBalloon.cs or RigidBody.cs). A simulation object offers an interface to the solver for simulating all it's particles. Additionally, it holds references to all its attached constraints (e.g. StretchingConstraint.cs). In turn, those constraints expose an interface to the simulation objects for adding / solving those constraints.

To handle collisions, the solver also makes use of the interface exposed by CollisionHandler.cs, which internally makes use of SpatialHashGrid.cs.

Related Work

We took inspiration for parts of our code from the following sources:

• One of the XPBD papers (see project proposal PowerPoint)
• Exercise 4 of the PBS course
• Matthias Mueller Cloth simulation physics tutorials
• Soft body tutorials from the blackedout01 YouTube channel

Additionally, we took the code for the NormalSolver.cs from here.