Table of Contents

Class Box2DEntityInstancing

Namespace
Stride.CommunityToolkit.Box2D
Assembly
Stride.CommunityToolkit.Box2D.dll

An EntityInstancing for Box2D bodies that stops working entirely once the bodies fall asleep, mirroring BepuEntityInstancing from Stride.CommunityToolkit.Bepu.

public class Box2DEntityInstancing : EntityInstancing, IInstancing
Inheritance
Box2DEntityInstancing
Implements
Inherited Members

Examples

game.AddInstancingSupport();

var instancing = new Box2DEntityInstancing();
var master = new Entity("Master") { new ModelComponent(model), new InstancingComponent { Type = instancing } };
master.Scene = scene;

// Instances carry a Box2DBodyComponent but no ModelComponent - the master draws them
foreach (var body in bodies) instancing.AddInstance(body);

Remarks

Box2D puts bodies to sleep when they come to rest, and a sleeping body's transform cannot change. That makes re-reading every transform, re-inverting every matrix and re-computing the bounding box pure waste, which is what the engine does forever once a pile settles. This class checks the bodies instead and reuses the previous frame's results while they are all asleep.

The check is a scan over the registered bodies, so it costs a little while things are moving - it gives up at the first awake body - and pays for itself many times over when they are not. Instances registered without a Box2DBodyComponent disable skipping altogether, since nothing indicates when they move; a component whose body id is invalid (not yet created, or destroyed) counts as asleep, because its transform cannot change either.

Properties

InstancesWithoutBody

Gets the number of registered instances that have no Box2DBodyComponent, and so prevent the sleep skip.

public int InstancesWithoutBody { get; }

Property Value

int

Methods

CanSkipUpdate()

Determines whether every registered body is asleep, in which case no transform can have changed.

protected override bool CanSkipUpdate()

Returns

bool

true when the previous frame's gather is still valid.

OnInstanceAdded(Entity)

Called after an instance is appended, for derived classes keeping parallel data.

protected override void OnInstanceAdded(Entity entity)

Parameters

entity Entity

The newly registered entity, now at index RegisteredInstanceCount - 1.

OnInstanceRemoved(int, int)

Called after an instance is removed by swapping the last one into its place, for derived classes keeping parallel data.

protected override void OnInstanceRemoved(int index, int lastIndex)

Parameters

index int

The index that was vacated and has just been overwritten.

lastIndex int

The index the surviving instance came from, now past the end.

Remarks

Derived data must mirror this exactly: copy lastIndex to index when they differ, then drop lastIndex.

OnInstancesCleared()

Called after every instance is unregistered, for derived classes keeping parallel data.

protected override void OnInstancesCleared()
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