[Peek] add extra logic to properly render PNG files with transparency

src/modules/peek/Peek.FilePreviewer/Previewers/ImagePreviewer/Helpers/ThumbnailHelper.cs

@@ -7,6 +7,8 @@ namespace Peek.FilePreviewer.Previewers
     using System;
     using System.Collections.Generic;
     using System.Runtime.InteropServices;
+    using System.Threading.Tasks;
+    using Microsoft.UI.Xaml.Media.Imaging;
     using Peek.Common;
     using Peek.Common.Models;
 
@@ -59,5 +61,32 @@ public static HResult GetThumbnail(string filename, out IntPtr hbitmap, NativeSi
 
             return hr;
         }
+
+        public static async Task<BitmapImage?> GetThumbnailAsync(string path, uint size)
+        {
+            BitmapImage? bitmapImage = null;
+
+            // preview image
+            var file = await Windows.Storage.StorageFile.GetFileFromPathAsync(path);
+            if (file == null)
+            {
+                return bitmapImage;
+            }
+
+            var imageStream = await file.GetThumbnailAsync(
+                Windows.Storage.FileProperties.ThumbnailMode.SingleItem,
+                size,
+                Windows.Storage.FileProperties.ThumbnailOptions.None);
+
+            if (imageStream == null)
+            {
+                return bitmapImage;
+            }
+
+            bitmapImage = new BitmapImage();
+            bitmapImage.SetSource(imageStream);
+
+            return bitmapImage;
+        }
     }
 }

src/modules/peek/Peek.FilePreviewer/Previewers/ImagePreviewer/ImagePreviewer.cs

@@ -13,7 +13,6 @@ namespace Peek.FilePreviewer.Previewers
     using System.Threading.Tasks;
     using CommunityToolkit.Mvvm.ComponentModel;
     using Microsoft.UI.Dispatching;
-    using Microsoft.UI.Xaml.Controls;
     using Microsoft.UI.Xaml.Media.Imaging;
     using Peek.Common;
     using Peek.Common.Extensions;
@@ -233,7 +232,8 @@ public static bool IsFileTypeSupported(string fileExt)
                 ".jif",
                 ".jpeg",
                 ".jpe",
-                ".png",
+
+                // ".png", // The current ImagePreviewer logic does not support transparency so PNG has it's own logic in PngPreviewer
                 ".tif",
                 ".tiff",
                 ".dib",

src/modules/peek/Peek.FilePreviewer/Previewers/PngPreviewer/PngPreviewer.cs

@@ -0,0 +1,117 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace Peek.FilePreviewer.Previewers
+{
+    using System;
+    using System.Collections.Generic;
+    using System.Drawing.Imaging;
+    using System.IO;
+    using System.Threading;
+    using System.Threading.Tasks;
+    using CommunityToolkit.Mvvm.ComponentModel;
+    using Microsoft.UI.Dispatching;
+    using Microsoft.UI.Xaml.Media.Imaging;
+    using Peek.Common;
+    using Windows.Foundation;
+    using Windows.Graphics.Imaging;
+    using Windows.Storage.Streams;
+    using File = Peek.Common.Models.File;
+
+    public partial class PngPreviewer : ObservableObject, IBitmapPreviewer
+    {
+        private readonly uint _png_image_size = 1280;
+
+        [ObservableProperty]
+        [NotifyPropertyChangedFor(nameof(IsPreviewLoaded))]
+        private BitmapSource? preview;
+
+        [ObservableProperty]
+        private PreviewState state;
+
+        public PngPreviewer(File file)
+        {
+            File = file;
+            Dispatcher = DispatcherQueue.GetForCurrentThread();
+
+            PropertyChanged += OnPropertyChanged;
+        }
+
+        public bool IsPreviewLoaded => preview != null;
+
+        private File File { get; }
+
+        private DispatcherQueue Dispatcher { get; }
+
+        private CancellationTokenSource _cancellationTokenSource = new CancellationTokenSource();
+
+        private CancellationToken CancellationToken => _cancellationTokenSource.Token;
+
+        public void Dispose()
+        {
+            _cancellationTokenSource.Dispose();
+            GC.SuppressFinalize(this);
+        }
+
+        public async Task<Size> GetPreviewSizeAsync()
+        {
+            var propertyImageSize = await PropertyHelper.GetImageSize(File.Path);
+            if (propertyImageSize != Size.Empty)
+            {
+                return propertyImageSize;
+            }
+
+            return await WICHelper.GetImageSize(File.Path);
+        }
+
+        public async Task LoadPreviewAsync()
+        {
+            State = PreviewState.Loading;
+
+            var previewTask = LoadPreviewImageAsync();
+
+            await Task.WhenAll(previewTask);
+
+            if (Preview == null)
+            {
+                State = PreviewState.Error;
+            }
+        }
+
+        public static bool IsFileTypeSupported(string fileExt)
+        {
+            return fileExt == ".png" ? true : false;
+        }
+
+        private void OnPropertyChanged(object? sender, System.ComponentModel.PropertyChangedEventArgs e)
+        {
+            if (e.PropertyName == nameof(Preview))
+            {
+                if (Preview != null)
+                {
+                    State = PreviewState.Loaded;
+                }
+            }
+        }
+
+        private Task LoadPreviewImageAsync()
+        {
+            var thumbnailTCS = new TaskCompletionSource();
+            Dispatcher.TryEnqueue(async () =>
+            {
+                if (CancellationToken.IsCancellationRequested)
+                {
+                    _cancellationTokenSource = new CancellationTokenSource();
+                    return;
+                }
+
+                Preview = await ThumbnailHelper.GetThumbnailAsync(File.Path, _png_image_size);
+
+                thumbnailTCS.SetResult();
+            });
+
+            return thumbnailTCS.Task;
+        }
+    }
+}

src/modules/peek/Peek.FilePreviewer/Previewers/PreviewerFactory.cs

@@ -10,7 +10,11 @@ public class PreviewerFactory
     {
         public IPreviewer Create(File file)
         {
-            if (ImagePreviewer.IsFileTypeSupported(file.Extension))
+            if (PngPreviewer.IsFileTypeSupported(file.Extension))
+            {
+                return new PngPreviewer(file);
+            }
+            else if (ImagePreviewer.IsFileTypeSupported(file.Extension))
             {
                 return new ImagePreviewer(file);
             }