sort photos by creation time

Program.cs

@@ -147,9 +147,10 @@ void main() {
 
 // FIXME: this should probably be IDisposable?
 public class Photo {
-  public string File;
+  public string Filename;
   public bool Loaded = false;
   public Vector2i Size;
+  public DateTime DateTimeOriginal;
   public string CameraModel = "";
   public string LensModel = "";
   public string FocalLength = "<unk>";
@@ -163,12 +164,14 @@ public class Photo {
   private Texture placeholder;
   private Image<Rgba32>? image = null;
 
-  public Photo(string file, Texture placeholder) {
-    File = file;
+  public Photo(string filename, Texture placeholder) {
+    Filename = filename;
     this.placeholder = placeholder;
     texture = placeholder;
 
-    ImageInfo info = Image.Identify(file);
+    DateTime creationTime = File.GetCreationTime(filename);  // Local time.
+    DateTimeOriginal = creationTime;
+    ImageInfo info = Image.Identify(filename);
     Size = new(info.Size.Width, info.Size.Height);
     ParseExif(info.Metadata.ExifProfile);
     TryParseRating(info.Metadata.XmpProfile, out Rating);
@@ -178,7 +181,7 @@ public class Photo {
     // 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.
-    Image<Rgba32> tmp = await Image.LoadAsync<Rgba32>(File);
+    Image<Rgba32> tmp = await Image.LoadAsync<Rgba32>(Filename);
     Util.RotateImageFromExif(tmp, Orientation);
     image = tmp;
   }
@@ -206,14 +209,34 @@ public class Photo {
     return false;
   }
 
+  // Exif (and other image metadata) reference, from the now-defunct Metadata Working Group:
+  // https://web.archive.org/web/20180919181934/http://www.metadataworkinggroup.org/pdf/mwg_guidance.pdf
+  //
+  // Specifically:
+  //
+  // In general, date/time metadata is being used to describe the following scenarios:
+  // * Date/time original specifies when a photo was taken
+  // * Date/time digitized specifies when an image was digitized
+  // * Date/time modified specifies when a file was modified by the user
+  //
+  // Original Date/Time – Creation date of the intellectual content (e.g. the photograph), rather than the creation date of the content being shown
+  // Exif DateTimeOriginal (36867, 0x9003) and SubSecTimeOriginal (37521, 0x9291)
+  // IPTC DateCreated (IIM 2:55, 0x0237) and TimeCreated (IIM 2:60, 0x023C)
+  // XMP (photoshop:DateCreated)
+  //
+  // Digitized Date/Time – Creation date of the digital representation
+  // Exif DateTimeDigitized (36868, 0x9004) and SubSecTimeDigitized (37522, 0x9292)
+  // IPTC DigitalCreationDate (IIM 2:62, 0x023E) and DigitalCreationTime (IIM 2:63, 0x023F)
+  // XMP (xmp:CreateDate)
+  //
+  // Modification Date/Time – Modification date of the digital image file
+  // Exif DateTime (306, 0x132) and SubSecTime (37520, 0x9290)
+  // XMP (xmp:ModifyDate)
   private void ParseExif(ExifProfile? exifs) {
     if (exifs == null) {
       return;
     }
 
-    // FIXME: when we write out images, we'll want to correct the Exif Orientation to 1.
-    // FIXME: handle date shot / edited (and sort by shot date?)
-
     IExifValue<ushort>? orientation;
     if (exifs.TryGetValue(ExifTag.Orientation, out orientation)) {
       Orientation = orientation.Value;
@@ -281,6 +304,23 @@ public class Photo {
         }
       }
     }
+
+    // FIXME: I think the iPhone stores time in UTC but other cameras report it in local time.
+    IExifValue<string>? dateTimeOriginal;
+    if (exifs.TryGetValue(ExifTag.DateTimeOriginal, out dateTimeOriginal)) {
+      DateTime date;
+      if (DateTime.TryParseExact(
+          dateTimeOriginal.Value ?? "",
+          "yyyy:MM:dd HH:mm:ss",
+          System.Globalization.CultureInfo.InvariantCulture,
+          System.Globalization.DateTimeStyles.AssumeLocal,
+          out date)) {
+        DateTimeOriginal = date;
+      } else {
+        Console.WriteLine($"*** WARNING: unexpected DateTimeOriginal value: {dateTimeOriginal.Value}");
+      }
+    }
+
     // foreach (IExifValue exif in exifs.Values) {
     //   Console.WriteLine(exif.Tag.ToString() + " " + exif.GetValue().ToString());
     // }
@@ -301,7 +341,7 @@ public class Photo {
 
   public string Description() {
     string shootingInfo = $"{FocalLength}, {FNumber} at {ExposureTime}, {IsoSpeed}";
-    return String.Format("{0,-40} {1,-50} {2}", shootingInfo, $"{CameraModel} {LensModel}", File);
+    return String.Format("{0,-40} {1,-50} {2}", shootingInfo, $"{CameraModel} {LensModel}", Filename);
   }
 }
 
@@ -603,8 +643,8 @@ public class Game : GameWindow {
 
     // Load textures from JPEGs.
     // 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(@"c:\users\colin\pictures\photos\2023\07\14\");
+    // 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\many-birds\");
@@ -617,11 +657,23 @@ 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) {
+    int compare = x.DateTimeOriginal.CompareTo(y.DateTimeOriginal);
+    if (compare != 0) {
+      return compare;
+    }
+    // If the photos have the same seconds value, sort by filename
+    // (since cameras usually increment the filename for successive shots.)
+    return x.Filename.CompareTo(y.Filename);
+  }
+
   protected override void OnUnload() {
     base.OnUnload();
   }