Add function "updateBodyInstances" to synchronize mesh instances with physics body instances. (#13576)

Author: carolhmj

packages/dev/core/src/Physics/v2/IPhysicsEnginePlugin.ts

@@ -123,6 +123,7 @@ export interface IPhysicsEnginePluginV2 {
     // body
     initBody(body: PhysicsBody, position: Vector3, orientation: Quaternion): void;
     initBodyInstances(body: PhysicsBody, mesh: Mesh): void;
+    updateBodyInstances(body: PhysicsBody, mesh: Mesh): void;
     removeBody(body: PhysicsBody): void;
     sync(body: PhysicsBody): void;
     syncTransform(body: PhysicsBody, transformNode: TransformNode): void;

packages/dev/core/src/Physics/v2/physicsBody.ts

@@ -84,6 +84,16 @@ export class PhysicsBody {
         physicsEngine.addBody(this);
     }
 
+    /**
+     * If a physics body is connected to an instanced node, update the number physic instances to match the number of node instances.
+     */
+    public updateBodyInstances() {
+        const m = this.transformNode as Mesh;
+        if (m.hasThinInstances) {
+            this._physicsPlugin.updateBodyInstances(this, m);
+        }
+    }
+
     /**
      * Sets the shape of the physics body.
      * @param shape - The shape of the physics body.