player and entity physics improvements

Window.cs

@@ -12,13 +12,24 @@ namespace Voxel
         public readonly int Height = height;
         public uint frames = 0;
         public double timeElapsed = 0;
-        public event Action<float> Update;
+
+        public event Action<float, float> Update;
+        public event Action Tick;
+
+        private double _tickTime;
+        public const double TICK_LENGTH = 1.0 / 20.0; // 20 TPS
 
         protected override void OnUpdateFrame(FrameEventArgs e)
         {
             base.OnUpdateFrame(e);
 
-            float deltaTime = (float)e.Time;
+            _tickTime += e.Time;
+
+            while (_tickTime >= TICK_LENGTH)
+            {
+                _tickTime -= TICK_LENGTH;
+                Tick(); // run exactly once per tick
+            }
 
             if (Input.GetKey(Keys.Escape))
             {
@@ -32,8 +43,6 @@ namespace Voxel
                 else
                     WindowState = WindowState.Normal;
             }
-
-            Update.Invoke(deltaTime);
         }
 
         protected override void OnRenderFrame(FrameEventArgs e)
@@ -44,6 +53,8 @@ namespace Voxel
 
             frames++;
             timeElapsed += e.Time;
+            float alpha = (float)(_tickTime / Window.TICK_LENGTH);
+            float deltaTime = (float)e.Time;
             if (timeElapsed >= 1)
             {
                 Console.WriteLine("FPS: " + frames.ToString());
@@ -51,6 +62,8 @@ namespace Voxel
                 frames = 0;
             }
 
+            Update.Invoke(deltaTime, alpha);
+
             Renderer.Render();
 
             SwapBuffers();