Fixed FPS issue.

FreedomFighter/Game1.cs

@@ -32,6 +32,11 @@ public class Game1 : Game
     int _fps, _fpsFrames;
     double _fpsTimer;
 
+    // precise 120Hz pacing (MonoGame's fixed-timestep Sleep overshoots and drops ticks)
+    const double TickSeconds = 1 / 120.0;
+    readonly System.Diagnostics.Stopwatch _frameClock = System.Diagnostics.Stopwatch.StartNew();
+    double _nextFrameTime;
+
     public Game1()
     {
         _graphics = new GraphicsDeviceManager(this)
@@ -42,8 +47,7 @@ public class Game1 : Game
         };
         Content.RootDirectory = "Content";
         IsMouseVisible = true;
-        IsFixedTimeStep = true;
+        IsFixedTimeStep = false;   // paced manually in EndDraw for an accurate 120Hz
-        TargetElapsedTime = TimeSpan.FromSeconds(1 / 120.0);
         Window.Title = "Freedom Fighter";
         Window.AllowUserResizing = true;
         Window.ClientSizeChanged += (_, _) =>
@@ -113,6 +117,21 @@ public class Game1 : Game
         }
     }
 
+    protected override void EndDraw()
+    {
+        base.EndDraw();
+
+        // hybrid sleep/spin wait until the next 1/120s boundary
+        _nextFrameTime += TickSeconds;
+        double now = _frameClock.Elapsed.TotalSeconds;
+        if (now > _nextFrameTime + 0.25)
+            _nextFrameTime = now;   // resync after a stall (window drag, load, etc.)
+        while (_nextFrameTime - _frameClock.Elapsed.TotalSeconds > 0.002)
+            System.Threading.Thread.Sleep(1);
+        while (_frameClock.Elapsed.TotalSeconds < _nextFrameTime)
+            System.Threading.Thread.SpinWait(50);
+    }
+
     protected override void Update(GameTime gameTime)
     {
         // all logic runs in Draw, matching the original's timer callback

FreedomFighter/Program.cs

@@ -1,17 +1,31 @@
 using System;
+using System.Runtime.InteropServices;
 
-using var game = new FreedomFighter.Game1();
+// 1ms timer resolution so the 120Hz fixed timestep's Thread.Sleep doesn't overshoot
-// debug aid: --shot <file> [frames] renders, saves the backbuffer to a PNG, and exits
+// (default ~15.6ms granularity caps the loop at 80-90 FPS; OmegaTimer did the same)
-var cmdArgs = Environment.GetCommandLineArgs();
+[DllImport("winmm.dll")] static extern uint timeBeginPeriod(uint ms);
-for (int i = 1; i < cmdArgs.Length - 1; i++)
+[DllImport("winmm.dll")] static extern uint timeEndPeriod(uint ms);
+timeBeginPeriod(1);
+
+try
 {
-    if (cmdArgs[i] == "--shot")
+    using var game = new FreedomFighter.Game1();
+    // debug aid: --shot <file> [frames] renders, saves the backbuffer to a PNG, and exits
+    var cmdArgs = Environment.GetCommandLineArgs();
+    for (int i = 1; i < cmdArgs.Length - 1; i++)
     {
-        game.ShotFile = cmdArgs[i + 1];
+        if (cmdArgs[i] == "--shot")
-        if (i + 2 < cmdArgs.Length && int.TryParse(cmdArgs[i + 2], out int frames))
+        {
-            game.ShotFrames = frames;
+            game.ShotFile = cmdArgs[i + 1];
+            if (i + 2 < cmdArgs.Length && int.TryParse(cmdArgs[i + 2], out int frames))
+                game.ShotFrames = frames;
+        }
+        if (cmdArgs[i] == "--level" && int.TryParse(cmdArgs[i + 1], out int level))
+            game.StartLevel = level;
     }
-    if (cmdArgs[i] == "--level" && int.TryParse(cmdArgs[i + 1], out int level))
+    game.Run();
-        game.StartLevel = level;
+}
+finally
+{
+    timeEndPeriod(1);
 }
-game.Run();