feat: improve UI/UX of font loading

QuickLook.Plugin/QuickLook.Plugin.FontViewer/ObservableFileStream.cs

@@ -0,0 +1,26 @@
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace QuickLook.Plugin.FontViewer;
+
+public class ObservableFileStream(string path, FileMode mode, FileAccess access, FileShare share) : FileStream(path, mode, access, share)
+{
+    public bool IsEndOfStream { get; protected set; } = false;
+
+    public override int Read(byte[] array, int offset, int count)
+    {
+        int result = base.Read(array, offset, count);
+        if (result == 0)
+            IsEndOfStream = true;
+        return result;
+    }
+
+    public override async Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
+    {
+        int result = await base.ReadAsync(buffer, offset, count, cancellationToken);
+        if (result == 0)
+            IsEndOfStream = true;
+        return result;
+    }
+}

QuickLook.Plugin/QuickLook.Plugin.FontViewer/Plugin.cs

@@ -19,6 +19,7 @@ using QuickLook.Common.Plugin;
 using System;
 using System.IO;
 using System.Linq;
+using System.Threading.Tasks;
 using System.Windows;
 
 namespace QuickLook.Plugin.FontViewer;
@@ -52,7 +53,12 @@ public class Plugin : IViewer
 
         context.ViewerContent = _panel;
         context.Title = Path.GetFileName(path);
+
+        _ = Task.Run(() =>
+        {
+            _ = _panel.WaitForFontSent();
             context.IsBusy = false;
+        });
     }
 
     public void Cleanup()

QuickLook.Plugin/QuickLook.Plugin.FontViewer/WebfontPanel.cs

@@ -26,6 +26,7 @@ using System.IO;
 using System.Linq;
 using System.Reflection;
 using System.Text;
+using System.Threading;
 
 namespace QuickLook.Plugin.FontViewer;
 
@@ -34,6 +35,7 @@ public class WebfontPanel : WebpagePanel
     protected const string _resourcePrefix = "QuickLook.Plugin.FontViewer.Resources.";
     protected internal static readonly Dictionary<string, byte[]> _resources = [];
     protected byte[] _homePage;
+    protected ObservableFileStream _fontStream = null;
 
     static WebfontPanel()
     {
@@ -153,10 +155,11 @@ public class WebfontPanel : WebpagePanel
 
                     if (File.Exists(localPath))
                     {
-                        var fileStream = new FileStream(localPath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite | FileShare.Delete);
+                        var fileStream = new ObservableFileStream(localPath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite | FileShare.Delete);
                         var response = _webView.CoreWebView2.Environment.CreateWebResourceResponse(
                             fileStream, 200, "OK", MimeTypes.GetContentType());
                         args.Response = response;
+                        _fontStream = fileStream; // Only the font request will set this
                     }
                 }
             }
@@ -168,6 +171,19 @@ public class WebfontPanel : WebpagePanel
         }
     }
 
+    public bool WaitForFontSent()
+    {
+        bool timeout = SpinWait.SpinUntil(
+            () => _fontStream is not null && _fontStream.IsEndOfStream,
+            TimeSpan.FromSeconds(1.5d) // The prediction is MAX 100MB
+        );
+
+        // Only when the `IsEndOfStream` is true
+        // Delay 15ms per MB for webview2 to render the font
+        if (timeout) Thread.Sleep(15 * (int)(_fontStream.Position / 1_048_576));
+        return timeout;
+    }
+
     public static bool ContainsKey(string key)
     {
         return _resources.ContainsKey(key);