add Timer class for tracking draw & update times (etc)

related issue: #33

GitOrigin-RevId: 3762a7a5c7becf83cc50f80d4e5bb6f27244a952

Shared/Timer.cs

@@ -0,0 +1,46 @@
+using System;
+using System.Diagnostics;
+
+namespace SemiColinGames {
+  class Timer {
+
+    private readonly Stopwatch stopwatch = new Stopwatch();
+    private readonly double targetTime;
+    private readonly string name;
+    private double startTime = 0.0;
+    private int[] histogram = new int[41];
+    private int totalFrames = 0;
+
+    public Timer(double targetTime, string name) {
+      this.targetTime = targetTime;
+      this.name = name;
+    }
+
+    public void Start() {
+      startTime = stopwatch.Elapsed.TotalSeconds;
+      stopwatch.Start();
+    }
+
+    public void Stop() {
+      stopwatch.Stop();
+      totalFrames++;
+      double frameTime = stopwatch.Elapsed.TotalSeconds - startTime;
+      int bucket = FMath.Clamp((int) (5.0f * frameTime / targetTime), 0, 40);
+      histogram[bucket]++;
+      if (totalFrames % 100 == 0) {
+        DumpStats();
+      }
+    }
+
+    public void DumpStats() {
+      Debug.WriteLine(name + ".DumpStats():");
+      for (int i = 0; i < histogram.Length - 1; i++) {
+        int value = histogram[i];
+        if (value > 0) {
+          Debug.WriteLine($"{i * 5}-{(i + 1) * 5}%: {histogram[i]}");
+        }
+      }
+      Debug.WriteLine($"200+%: {histogram[histogram.Length - 1]}");
+    }
+  }
+}