fix: correct timestep update

Author: Neosoulink

examples/jsm/physics/RapierPhysics.js

@@ -349,10 +349,11 @@ export class Physic {
 	/**
 	 * @description Update the physic world.
 	 *
-	 * @param {number | undefined} delta
+	 * @param {number | undefined} timestep The timestep length, in seconds.
 	 */
-	step(delta = undefined) {
-		this.world.step(delta);
+	step(timestep = undefined) {
+		if (typeof timestep === "number") this.world.timestep = timestep;
+		this.world.step();
 
 		for (let i = 0, l = this.dynamicObjects.length; i < l; i++) {
 			const object = this.dynamicObjects[i];

examples/physics_rapier_instancing.html

@@ -173,9 +173,11 @@
 
 			}
 
-			function animate() {
+			const clock = new THREE.Clock();
 
-				physics.step();
+ 			function animate() {
+
+				physics.step( clock.getDelta() );
 
 				controls.update();