add fps counter

Program.cs

@@ -10,12 +10,33 @@ using SixLabors.ImageSharp.Metadata.Profiles.Exif;
 using SixLabors.ImageSharp.Metadata.Profiles.Xmp;
 using SixLabors.ImageSharp.Drawing.Processing;
 using SixLabors.ImageSharp.Drawing;
+using System;
 using System.Diagnostics;
 using System.Runtime.CompilerServices;
 using System.Xml.Linq;
 
 namespace SemiColinGames;
 
+public class FpsCounter {
+  private readonly int[] frameTimes = new int[60];
+  private double fps = 0;
+  private int idx = 0;
+
+  public int Fps {
+    get => (int) Math.Ceiling(fps);
+  }
+
+  public void Update() {
+    var now = Environment.TickCount;  // ms
+    if (frameTimes[idx] != 0) {
+      var timeElapsed = now - frameTimes[idx];
+      fps = 1000.0 * frameTimes.Length / timeElapsed;
+    }
+    frameTimes[idx] = now;
+    idx = (idx + 1) % frameTimes.Length;
+  }
+}
+
 public class CameraInfo {
   public readonly Vector2i Resolution;
 
@@ -499,6 +520,7 @@ public class Game : GameWindow {
   private static Texture TEXTURE_BLACK = new(new Image<Rgba32>(1, 1, new Rgba32(0, 0, 0)));
 
   UiGeometry geometry = new();
+  FpsCounter fpsCounter = new();
 
   // Input handling.
   long downTimer = Int64.MaxValue;
@@ -526,6 +548,7 @@ public class Game : GameWindow {
 
   protected override void OnUpdateFrame(FrameEventArgs e) {
     base.OnUpdateFrame(e);
+    Console.WriteLine("update");
     long now = DateTime.Now.Ticks;
 
     KeyboardState input = KeyboardState;
@@ -726,6 +749,8 @@ public class Game : GameWindow {
 
   protected override void OnRenderFrame(FrameEventArgs e) {
     base.OnRenderFrame(e);
+    Console.WriteLine("render");
+    fpsCounter.Update();
 
     LoadAndUnloadImagesAsync();
 
@@ -767,6 +792,7 @@ public class Game : GameWindow {
     // Draw status box.
     DrawFilledBox(geometry.StatusBox, Color4.Black);
     DrawText(activePhoto.Description(), geometry.StatusBox.Min.X + 80, geometry.StatusBox.Min.Y);
+    DrawText($" FPS: {fpsCounter.Fps}", geometry.StatusBox.Max.X - 76, geometry.StatusBox.Min.Y);
     if (activePhoto.Loaded) {
       DrawText($"{(scale * 100):F1}%", geometry.StatusBox.Min.X, geometry.StatusBox.Min.Y);
     }
@@ -860,7 +886,8 @@ static class Program {
     }
     Console.WriteLine($"best monitor: {bestMonitor.HorizontalResolution}x{bestMonitor.VerticalResolution}");
     GameWindowSettings gwSettings = new();
-    gwSettings.RenderFrequency = 60.0;
+    gwSettings.UpdateFrequency = 30.0;
+    gwSettings.RenderFrequency = 30.0;
 
     NativeWindowSettings nwSettings = new();
     nwSettings.WindowState = WindowState.Normal;