Simple Constraint

One constraint, doing one thing: a distance servo holding two spheres three units apart, pulling them together or pushing them apart until they settle there. It is the gentlest possible introduction to Bepu constraints, and the shortest - everything else in the constraint family builds on the same pattern of naming two bodies and describing the relationship you want between them.

The Program.cs file shows how to:

Connecting two bodies with DistanceServoConstraintComponent
Setting a target distance and watching the solver reach it
How a constraint component attaches to an entity
Reading the result against a ground reference grid
Picking a sphere up with GrabberScript and feeling the servo pull the other along
Using helpers: SceneSetup3D, UseSkybox, AddGroundGizmo

Simple Constraint

View on GitHub.

using Stride.BepuPhysics;
using Stride.BepuPhysics.Constraints;
using Stride.CommunityToolkit.Bepu;
using Stride.CommunityToolkit.Engine;
using Stride.CommunityToolkit.Rendering.ProceduralModels;
using Stride.CommunityToolkit.Rendering.Overlay;
using Stride.CommunityToolkit.Skyboxes;
using Stride.Core.Mathematics;
using Stride.Engine;

using var game = new Game();

game.Run(new SceneSetup3D { Profiler = true }.UseBepu().UseSkybox(), start: Start);

void Start(Scene scene)
{
    game.AddGroundGizmo(new(-5, 0, -5), showAxisName: true);

    // Left mouse picks either sphere up; the servo drags the other one along (GrabberScript, see E05_3D_Grabber).
    game.AddGrabber();

    var overlay = TextOverlay.GetOrCreate(game);
    overlay.SectionGap = 0;
    overlay.AddSection("Constraint", static () =>
    [
        new("Left mouse", "Pick a sphere up, carry it, throw it", Color.Yellow),
        new("Mouse wheel", "Carry distance", Color.Yellow),
        new("T", "Hold and move the mouse to turn the held sphere", Color.Yellow),
        new(""),
        new("A distance servo holds the spheres 3 units apart", Color.LightGray),
        new("Carry one and the other follows", Color.LightGray),
    ]);

    var capsule = game.CreatePrimitive(Primitive3D.Capsule(), new() { Position = new Vector3(0, 3, 0) });
    capsule.Scene = scene;

    var sphere = game.CreatePrimitive(Primitive3D.Sphere(), new()
    {
        Material = game.CreateMaterial(Color.Gold),
        Position = new Vector3(0.1f, 5, -0.3f),
    });

    var connectedSphere = game.CreatePrimitive(Primitive3D.Sphere(), new() { Position = new Vector3(-2f, 1, -2f) });

    // A distance servo holds the two spheres at a target distance: grab one and the other follows
    sphere.Add(new DistanceServoConstraintComponent
    {
        A = sphere.Get<BodyComponent>(),
        B = connectedSphere.Get<BodyComponent>(),
        TargetDistance = 3.0f,
    });

    sphere.Scene = scene;
    connectedSphere.Scene = scene;
}

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Simple Constraint