[Peek] Fix thumbnails being created and not used. Fix icon bitmaps leaking memory. Simplify ImagePreviewer.

src/modules/peek/Peek.Common/Models/Win32/IShellItemImageFactory.cs

@@ -20,20 +20,11 @@ HResult GetImage(
     }
 
     [StructLayout(LayoutKind.Sequential)]
-    public struct NativeSize
+    public struct NativeSize(int width, int height)
     {
-        private int width;
-        private int height;
+        public int Width { get; set; } = width;
 
-        public int Width
-        {
-            set { width = value; }
-        }
-
-        public int Height
-        {
-            set { height = value; }
-        }
+        public int Height { get; set; } = height;
     }
 
     [Flags]

src/modules/peek/Peek.FilePreviewer/Previewers/Drive/DrivePreviewer.cs

@@ -82,7 +82,7 @@ public async Task LoadPreviewAsync(CancellationToken cancellationToken)
             }
 
             cancellationToken.ThrowIfCancellationRequested();
-            var iconBitmap = await IconHelper.GetIconAsync(Item.Path, cancellationToken);
+            var iconBitmap = await ThumbnailHelper.GetIconAsync(Item.Path, cancellationToken);
             preview.IconPreview = iconBitmap ?? new SvgImageSource(new Uri("ms-appx:///Assets/Peek/DefaultFileIcon.svg"));
 
             Preview = preview;

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

@@ -0,0 +1,102 @@
+// 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.
+
+using System;
+using System.Runtime.InteropServices;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.UI.Xaml.Media;
+using Peek.Common;
+using Peek.Common.Models;
+
+namespace Peek.FilePreviewer.Previewers.Helpers;
+
+/// <summary>
+/// Create thumbnail or icon images for a file, or retrieve them from the Windows Explorer thumbnail and icon caches.
+/// </summary>
+/// <remarks>Inspired by https://stackoverflow.com/questions/21751747/extract-thumbnail-for-any-file-in-windows</remarks>
+public static class ThumbnailHelper
+{
+    // The maximum size Explorer's thumbnail cache currently supports. Used for cache retrieval.
+    private static readonly NativeSize MaxThumbnailSize = new(2560, 2560);
+
+    // Default size for all previewers except ImagePreviewer.
+    private static readonly NativeSize DefaultThumbnailSize = new(256, 256);
+
+    // Used to retrieve the Shell Item for a given Windows Explorer resource, so its thumbnail/icon can be retrieved.
+    private static Guid _shellItem2Guid = new("7E9FB0D3-919F-4307-AB2E-9B1860310C93");
+
+    /// <summary>
+    /// Get a file's icon bitmap.
+    /// </summary>
+    /// <param name="path">Path to the file.</param>
+    /// <param name="cancellationToken">The async task cancellation token.</param>
+    /// <returns>An <see cref="ImageSource"/> corresponding to the file's icon bitmap, or null if retrieval failed.</returns>
+    /// <remarks>If a cached icon cannot be found, a new icon will be created and added to the Explorer icon cache.</remarks>
+    public static async Task<ImageSource?> GetIconAsync(string path, CancellationToken cancellationToken)
+    {
+        return await GetImageAsync(path, ThumbnailOptions.BiggerSizeOk | ThumbnailOptions.IconOnly, true, cancellationToken);
+    }
+
+    /// <summary>
+    /// Get a file's thumbnail bitmap.
+    /// </summary>
+    /// <param name="path">Path to the file.</param>
+    /// <param name="cancellationToken">The async task cancellation token.</param>
+    /// <returns>An <see cref="ImageSource"/> corresponding to the file's thumbnail bitmap, or null if retrieval failed.</returns>
+    /// <remarks>If a cached thumbnail cannot be found, a new thumbnail will be created and added to the Explorer thumbnail cache.</remarks>
+    public static async Task<ImageSource?> GetThumbnailAsync(string path, CancellationToken cancellationToken)
+    {
+        return await GetImageAsync(path, ThumbnailOptions.BiggerSizeOk | ThumbnailOptions.ThumbnailOnly, true, cancellationToken);
+    }
+
+    /// <summary>
+    /// Get the highest-resolution image available for a file from the Explorer thumbnail and icon caches.
+    /// </summary>
+    /// <param name="path">Path to the file.</param>
+    /// <param name="supportsTransparency">Whether the file's type supports transparency. Set to true for PNG image files.</param>
+    /// <param name="cancellationToken">The async task cancellation token.</param>
+    /// <returns>An <see cref="ImageSource"/> corresponding to the thumbnail or icon, or null if there is no icon or thumbnail cached for the file.</returns>
+    public static async Task<ImageSource?> GetCachedThumbnailAsync(string path, bool supportsTransparency, CancellationToken cancellationToken)
+    {
+        return await GetImageAsync(path, ThumbnailOptions.InCacheOnly, supportsTransparency, cancellationToken);
+    }
+
+    private static async Task<ImageSource?> GetImageAsync(string path, ThumbnailOptions options, bool supportsTransparency, CancellationToken cancellationToken)
+    {
+        IntPtr hBitmap = IntPtr.Zero;
+        IShellItem? nativeShellItem = null;
+        bool checkCacheOnly = options.HasFlag(ThumbnailOptions.InCacheOnly);
+
+        try
+        {
+            int retCode = NativeMethods.SHCreateItemFromParsingName(path, IntPtr.Zero, ref _shellItem2Guid, out nativeShellItem);
+            if (retCode != 0)
+            {
+                throw Marshal.GetExceptionForHR(retCode)!;
+            }
+
+            cancellationToken.ThrowIfCancellationRequested();
+
+            HResult hr = ((IShellItemImageFactory)nativeShellItem).GetImage(checkCacheOnly ? MaxThumbnailSize : DefaultThumbnailSize, options, out hBitmap);
+
+            cancellationToken.ThrowIfCancellationRequested();
+
+            return hr == HResult.Ok ? await BitmapHelper.GetBitmapFromHBitmapAsync(hBitmap, supportsTransparency, cancellationToken) : null;
+        }
+        finally
+        {
+            // Delete the unmanaged bitmap resource.
+            if (hBitmap != IntPtr.Zero)
+            {
+                NativeMethods.DeleteObject(hBitmap);
+            }
+
+            if (nativeShellItem != null)
+            {
+                Marshal.ReleaseComObject(nativeShellItem);
+            }
+        }
+    }
+}

src/modules/peek/Peek.FilePreviewer/Previewers/MediaPreviewer/AudioPreviewer.cs

@@ -87,8 +87,8 @@ await Dispatcher.RunOnUiThread(async () =>
                 {
                     cancellationToken.ThrowIfCancellationRequested();
 
-                    var thumbnail = await IconHelper.GetThumbnailAsync(Item.Path, cancellationToken)
-                        ?? await IconHelper.GetIconAsync(Item.Path, cancellationToken);
+                    var thumbnail = await ThumbnailHelper.GetThumbnailAsync(Item.Path, cancellationToken)
+                        ?? await ThumbnailHelper.GetIconAsync(Item.Path, cancellationToken);
 
                     cancellationToken.ThrowIfCancellationRequested();