From 7d685e8b46574f0925087f4652b8809dade1fe68 Mon Sep 17 00:00:00 2001
From: "nicogo.eth" <Nicogo1705@users.noreply.github.com>
Date: Wed, 7 Oct 2026 12:57:10 +0200
Subject: [PATCH] [Physics] fix: MaxStepPerFrame now bounds steps per frame, -1
 no longer freezes the simulation

The guard `stepCount < MaxStepPerFrame || MaxStepPerFrame != -1` did not depend
on stepCount: any cap other than -1 never bounded the loop, and -1 never ran a step.

Fixes #3522

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
---
 .../Stride.BepuPhysics.Tests/BepuTests.cs         | 15 +++++++++++++++
 .../Stride.BepuPhysics/BepuSimulation.cs          |  2 +-
 .../Stride.BepuPhysics/Module.cs                  |  1 +
 3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/sources/engine/Stride.BepuPhysics/Stride.BepuPhysics.Tests/BepuTests.cs b/sources/engine/Stride.BepuPhysics/Stride.BepuPhysics.Tests/BepuTests.cs
index 32323b7cf..a7ab00eb0 100644
--- a/sources/engine/Stride.BepuPhysics/Stride.BepuPhysics.Tests/BepuTests.cs
+++ b/sources/engine/Stride.BepuPhysics/Stride.BepuPhysics.Tests/BepuTests.cs
@@ -591,6 +591,21 @@ namespace Stride.BepuPhysics.Tests
             RunGameTest(game);
         }
 
+        [Theory]
+        [InlineData(3, 10, 3)]
+        [InlineData(3, 2, 2)]
+        [InlineData(-1, 10, 10)]
+        public static void MaxStepPerFrameTest(int maxStepPerFrame, int pendingSteps, int expectedSteps)
+        {
+            using var simulation = new BepuSimulation { MaxStepPerFrame = maxStepPerFrame };
+            int steps = 0;
+            simulation.Register(new SimUpdateListener { SimUpdate = () => steps++ });
+
+            simulation.Update(simulation.FixedTimeStep * pendingSteps);
+
+            Assert.Equal(expectedSteps, steps);
+        }
+
         private class SimUpdateListener : ScriptComponent, ISimulationUpdate
         {
             public Action? SimUpdate, AfterSimUpdate;
diff --git a/sources/engine/Stride.BepuPhysics/Stride.BepuPhysics/BepuSimulation.cs b/sources/engine/Stride.BepuPhysics/Stride.BepuPhysics/BepuSimulation.cs
index ba193cd4a..86be60e4c 100644
--- a/sources/engine/Stride.BepuPhysics/Stride.BepuPhysics/BepuSimulation.cs
+++ b/sources/engine/Stride.BepuPhysics/Stride.BepuPhysics/BepuSimulation.cs
@@ -731,7 +731,7 @@ public sealed class BepuSimulation : IDisposable
         // TimeSpan multiplication is lossy, skipping mult when we can
         _remainingUpdateTime += TimeScale == 1f ? elapsed : elapsed * TimeScale;
 
-        for (int stepCount = 0; _remainingUpdateTime >= FixedTimeStep && (stepCount < MaxStepPerFrame || MaxStepPerFrame != -1); stepCount++, _remainingUpdateTime -= FixedTimeStep)
+        for (int stepCount = 0; _remainingUpdateTime >= FixedTimeStep && (MaxStepPerFrame == -1 || stepCount < MaxStepPerFrame); stepCount++, _remainingUpdateTime -= FixedTimeStep)
         {
             if (_softStartScheduled)
             {
diff --git a/sources/engine/Stride.BepuPhysics/Stride.BepuPhysics/Module.cs b/sources/engine/Stride.BepuPhysics/Stride.BepuPhysics/Module.cs
index 80f3a0b72..1e4717a9c 100644
--- a/sources/engine/Stride.BepuPhysics/Stride.BepuPhysics/Module.cs
+++ b/sources/engine/Stride.BepuPhysics/Stride.BepuPhysics/Module.cs
@@ -9,6 +9,7 @@ using Stride.Core.Reflection;
 [assembly: InternalsVisibleTo("Stride.BepuPhysics.Debug")]
 [assembly: InternalsVisibleTo("Stride.BepuPhysics.Navigation")]
 [assembly: InternalsVisibleTo("Stride.BepuPhysics.Soft")]
+[assembly: InternalsVisibleTo("Stride.BepuPhysics.Tests")]
 
 namespace Stride.BepuPhysics;