start work on filtering by rating

Program.cs

@@ -563,6 +563,7 @@ public class Game : GameWindow {
   int VertexBufferObject;
   int ElementBufferObject;
   int VertexArrayObject;
+  List<Photo> allPhotos = new();
   List<Photo> photos = new();
   HashSet<int> loadedImages = new();
   int photoIndex = 0;
@@ -644,28 +645,42 @@ public class Game : GameWindow {
     // Make sure the photoIndex is actually valid.
     photoIndex = Math.Clamp(photoIndex, 0, photos.Count - 1);
 
+    // Handle presses of the "rating" keys -- 0-5 and `.
+    // A normal press just sets the rating of the current photo.
+    // If the user is holding "shift", we instead filter to only show photos of that rating or higher.
+    int rating = -1;
+
     if (input.IsKeyPressed(Keys.D0) || input.IsKeyPressed(Keys.GraveAccent)) {
-      photos[photoIndex].Rating = 0;
+      rating = 0;
     }
 
     if (input.IsKeyPressed(Keys.D1)) {
-      photos[photoIndex].Rating = 1;
+      rating = 1;
     }
 
     if (input.IsKeyPressed(Keys.D2)) {
-      photos[photoIndex].Rating = 2;
+      rating = 2;
     }
 
     if (input.IsKeyPressed(Keys.D3)) {
-      photos[photoIndex].Rating = 3;
+      rating = 3;
     }
 
     if (input.IsKeyPressed(Keys.D4)) {
-      photos[photoIndex].Rating = 4;
+      rating = 4;
     }
 
     if (input.IsKeyPressed(Keys.D5)) {
-      photos[photoIndex].Rating = 5;
+      rating = 5;
+    }
+
+    if (rating >= 0) {
+      bool shifted = input.IsKeyDown(Keys.LeftShift) || input.IsKeyDown(Keys.RightShift);
+      if (shifted) {
+        FilterByRating(rating);
+      } else {
+        photos[photoIndex].Rating = rating;
+      }
     }
 
     if (input.IsKeyPressed(Keys.Q)) {
@@ -693,6 +708,10 @@ public class Game : GameWindow {
     }
   }
 
+  void FilterByRating(int rating) {
+    Console.WriteLine("filter to " + rating);
+  }
+
   protected override void OnLoad() {
     base.OnLoad();
 
@@ -741,11 +760,12 @@ public class Game : GameWindow {
       string file = files[i];
       if (file.ToLower().EndsWith(".jpg")) {
         Photo photo = new Photo(file, TEXTURE_BLACK);
-        photos.Add(photo);
+        allPhotos.Add(photo);
       }
     }
 
-    photos.Sort(ComparePhotosByDate);
+    allPhotos.Sort(ComparePhotosByDate);
+    photos = allPhotos;
   }
 
   private static int ComparePhotosByDate(Photo x, Photo y) {