load and unload images dynamically

Program.cs

@@ -177,7 +177,7 @@ public class Photo {
     TryParseRating(info.Metadata.XmpProfile, out Rating);
   }
 
-  public async void Load() {
+  public async void LoadAsync() {
     // We don't assign to this.image until Load() is done, because we might
     // edit the image due to rotation (etc) and don't want to try generating
     // a texture for it until that's already happened.
@@ -186,6 +186,13 @@ public class Photo {
     image = tmp;
   }
 
+  public void Unload() {
+    if (texture != placeholder) {
+      texture.Dispose();
+      texture = placeholder;
+    }
+  }
+
   private bool TryParseRating(XmpProfile? xmp, out int rating) {
     rating = 0;
     if (xmp == null) {
@@ -320,10 +327,6 @@ public class Photo {
         Console.WriteLine($"*** WARNING: unexpected DateTimeOriginal value: {dateTimeOriginal.Value}");
       }
     }
-
-    // foreach (IExifValue exif in exifs.Values) {
-    //   Console.WriteLine(exif.Tag.ToString() + " " + exif.GetValue().ToString());
-    // }
   }
 
   public Texture Texture() {
@@ -512,6 +515,7 @@ public class Game : GameWindow {
   int ElementBufferObject;
   int VertexArrayObject;
   List<Photo> photos = new();
+  HashSet<int> loadedImages = new();
   int photoIndex = 0;
   int ribbonIndex = 0;
   Shader shader = new();
@@ -606,7 +610,7 @@ public class Game : GameWindow {
     }
   }
 
-  protected override async void OnLoad() {
+  protected override void OnLoad() {
     base.OnLoad();
 
     GL.ClearColor(0f, 0f, 0f, 1f);
@@ -642,12 +646,12 @@ public class Game : GameWindow {
     GL.EnableVertexAttribArray(texCoordLocation);
     GL.VertexAttribPointer(texCoordLocation, 2, VertexAttribPointerType.Float, false, 5 * sizeof(float), 3 * sizeof(float));
 
-    // Load textures from JPEGs.
+    // Load photos from a directory.
     // string[] files = Directory.GetFiles(@"c:\users\colin\desktop\photos-test\");
     // string[] files = Directory.GetFiles(@"c:\users\colin\pictures\photos\2023\07\14\");
-    string[] files = Directory.GetFiles(@"G:\DCIM\100EOSR6\");
+    // string[] files = Directory.GetFiles(@"G:\DCIM\100EOSR6\");
     // string[] files = Directory.GetFiles(@"C:\Users\colin\Pictures\photos\2018\06\23");
-    // string[] files = Directory.GetFiles(@"C:\Users\colin\Desktop\Germany all\104D7000");
+    string[] files = Directory.GetFiles(@"C:\Users\colin\Desktop\Germany all\104D7000");
     // string[] files = Directory.GetFiles(@"C:\Users\colin\Desktop\many-birds\");
 
     for (int i = 0; i < files.Count(); i++) {
@@ -659,10 +663,6 @@ public class Game : GameWindow {
     }
 
     photos.Sort(ComparePhotosByDate);
-
-    for (int i = 0; i < 40 && i < photos.Count; i++) {
-      await Task.Run( () => { photos[i].Load(); });
-    }
   }
 
   private static int ComparePhotosByDate(Photo x, Photo y) {
@@ -679,11 +679,36 @@ public class Game : GameWindow {
     base.OnUnload();
   }
 
+  private async void LoadAndUnloadImagesAsync() {
+    int minUnloadedImage = Math.Max(0, photoIndex - 40);
+    int maxUnloadedImage = Math.Min(photoIndex + 40, photos.Count - 1);
+    int minLoadedImage = Math.Max(0, photoIndex - 20);
+    int maxLoadedImage = Math.Min(photoIndex + 20, photos.Count - 1);
+    // First, unload images that are far outside our window.
+    foreach (int i in loadedImages) {
+      if (i < minUnloadedImage || i > maxUnloadedImage) {
+        loadedImages.Remove(i);
+        photos[i].Unload();
+        Console.WriteLine("unloading " + i);
+      }
+    }
+    // Then, start loading any images that aren't in our window.
+    for (int i = minLoadedImage; i <= maxLoadedImage; i++) {
+      if (!loadedImages.Contains(i)) {
+        Console.WriteLine("loading " + i);
+        loadedImages.Add(i);
+        await Task.Run( () => { photos[i].LoadAsync(); });
+      }
+    }
+  }
+
   protected override void OnRenderFrame(FrameEventArgs e) {
     base.OnRenderFrame(e);
 
+    LoadAndUnloadImagesAsync();
+
     GL.Clear(ClearBufferMask.ColorBufferBit);
-    GL.BindBuffer(BufferTarget.ArrayBuffer, VertexBufferObject);
+    GL.BindBuffer(BufferTarget.ArrayBuffer, VertexBufferObject);  HashSet<int> loadedImages = new();
     GL.ActiveTexture(TextureUnit.Texture0);
 
     Photo activePhoto = photos[photoIndex];
@@ -829,4 +854,3 @@ static class Program {
     }
   }
 }
-