Add prefetching logic.

Author: adam-azarchs

PhotoCull/PhotoCullWindow.xaml.cs

@@ -187,6 +187,15 @@ private async void onClickSecond(object sender, RoutedEventArgs e) {
             await reject(true);
         }
 
+        private void prefetch() {
+            var photos = this.Photos;
+            if (photos.Count > 2) {
+                foreach (var p in photos.Take(3)) {
+                    p.Prefetch();
+                }
+            }
+        }
+
         private async Task reject(bool first) {
             var photos = this.Photos;
             if (photos.Count == 0) {
@@ -224,6 +233,7 @@ private async Task reject(bool first) {
             good.MarkedForDeletion = false;
             this.deleteButton.IsEnabled = true;
             this.photoList.SelectedValue = null;
+            this.prefetch();
         }
 
         private async void onDistinctFirst(object sender, RoutedEventArgs e) {
@@ -277,6 +287,7 @@ private async Task distinct(bool moveFirst) {
             }
             this.deleteButton.IsEnabled = photos.Any(p => p.MarkedForDeletion);
             this.photoList.SelectedValue = null;
+            this.prefetch();
         }
 
         private static bool debugging() {

PhotoTagger.Imaging/Photo.cs

@@ -23,6 +23,23 @@ public Photo(string f) {
             SlidingExpiration = TimeSpan.FromSeconds(10),
         };
 
+        /// <summary>
+        /// Begin the process of loading the full size image.
+        /// </summary>
+        public void Prefetch() {
+            var imageRef = this.fullImageRef;
+            if (this.setFrom == null ||
+                this.loader == null) {
+                // Queue this for prefetch as soon as the metadata is loaded.
+                Interlocked.CompareExchange(ref this.fullIsLoading, -1, 0);
+            } else if (!this.Disposed && (
+                 imageRef == null ||
+                 !imageRef.TryGetTarget(out BitmapImage _)) &&
+                 Interlocked.Exchange(ref this.fullIsLoading, 1) <= 0) {
+                this.loader?.EnqueueFullSizeRead(this, this.setFrom);
+            }
+        }
+
         public BitmapImage FullImage {
             get {
                 var imageRef = this.fullImageRef;
@@ -36,7 +53,9 @@ public BitmapImage FullImage {
                     return target;
                 } else {
                     if (this.setFrom != null &&
-                        Interlocked.Exchange(ref this.fullIsLoading, 1) == 0) {
+                        this.loader != null &&
+                        !this.Disposed &&
+                        Interlocked.Exchange(ref this.fullIsLoading, 1) <= 0) {
                         this.loader?.EnqueueFullSizeRead(this, this.setFrom);
                     }
                     return this.ThumbImage;
@@ -49,20 +68,17 @@ public BitmapImage FullImage {
                             new PropertyChangedEventArgs(nameof(FullImage)));
                     }
                     MemoryCache.Default.Remove(this.FileName);
+                    fullIsLoading = 0;
                     return;
                 } else if (this.fullImageRef == null) {
                     this.fullImageRef = new WeakReference<BitmapImage>(value);
                 } else {
                     this.fullImageRef.SetTarget(value);
                 }
-                fullIsLoading = 0;
                 Thread.MemoryBarrier();
+                fullIsLoading = 0;
                 this.PropertyChanged?.Invoke(this,
                     new PropertyChangedEventArgs(nameof(FullImage)));
-                MemoryCache.Default.Set(
-                    this.FileName,
-                    value,
-                    cachePolicy);
             }
         }
 
@@ -72,6 +88,9 @@ public BitmapImage ThumbImage {
             }
             set {
                 SetValue(ThumbImageProperty, value);
+                if (fullIsLoading < 0) {
+                    this.Prefetch();
+                }
                 this.PropertyChanged?.Invoke(this,
                     new PropertyChangedEventArgs(nameof(FullImage)));
             }

PhotoTagger.Wpf/PhotoList.xaml.cs

@@ -50,13 +50,16 @@ public ReadOnlyObservableCollection<Photo> Selected {
             }
         }
 
+        public event SelectionChangedEventHandler OnSelectionChanged;
+
         private void onSelectionChanged(object sender, SelectionChangedEventArgs e) {
             foreach (var item in e.RemovedItems) {
                 this.selected.Remove(item as Photo);
             }
             foreach (var item in e.AddedItems) {
                 this.selected.Add(item as Photo);
             }
+            OnSelectionChanged?.Invoke(sender, e);
         }
 
 

PhotoTagger/TaggerWindow.xaml

@@ -45,7 +45,8 @@
             <ptwpf:PhotoList Grid.Row="0"
                              x:Name="photoList"
                              SelectionMode="Extended"
-                             Photos="{Binding Photos, ElementName=window}"/>
+                             Photos="{Binding Photos, ElementName=window}"
+                             OnSelectionChanged="onSelectionChanged" />
             <StackPanel Grid.Row="1">
                 <Button Content="Add images..."
                         Click="addImagesEvent" />

PhotoTagger/TaggerWindow.xaml.cs

@@ -35,13 +35,27 @@ void photoCollectionChanged(object sender, NotifyCollectionChangedEventArgs e) {
                         photo.PropertyChanged += photoChanged;
                     }
                 }
+                foreach (var item in e.NewItems.OfType<Photo>().Take(3)) {
+                    item.Prefetch();
+                }
             }
             if (e.OldItems != null) {
                 // New items are always unchanged to begin.
                 this.commitButton.IsEnabled = this.Photos.Any(p => p.IsChanged);
             }
         }
 
+        private void onSelectionChanged(object sender, SelectionChangedEventArgs e) {
+            var photos = this.Photos;
+            foreach (var photo in e.AddedItems.OfType<Photo>().Take(3)) {
+                photo.Prefetch();
+                var i = photos.IndexOf(photo);
+                if (i >= 0 && i < photos.Count - 2) {
+                    photos[i + 1].Prefetch();
+                }
+            }
+        }
+
         void photoChanged(object sender, PropertyChangedEventArgs e) {
             this.commitButton.IsEnabled = this.Photos.Any(p => p.IsChanged);
         }