Fix image viewer copy without transparency support

QuickLook.Plugin/QuickLook.Plugin.ImageViewer/NativeMethods/ClipboardEx.cs

@@ -0,0 +1,65 @@
+using System.Drawing;
+using System.Drawing.Imaging;
+using System.IO;
+using System.Runtime.InteropServices;
+using System.Threading;
+using System.Windows;
+using System.Windows.Media.Imaging;
+using Clipboard = System.Windows.Forms.Clipboard;
+
+namespace QuickLook.Plugin.ImageViewer.NativeMethods;
+
+internal static class ClipboardEx
+{
+    public static void SetClipboardImage(this BitmapSource img)
+    {
+        if (img == null)
+        {
+            return;
+        }
+
+        var thread = new Thread((img) =>
+        {
+            if (img == null)
+            {
+                return;
+            }
+
+            var image = (BitmapSource)img;
+
+            try
+            {
+                Clipboard.Clear();
+            }
+            catch (ExternalException) { }
+
+            try
+            {
+                using var pngMemStream = new MemoryStream();
+                using var bitmpa = image.ToBitmap();
+                var data = new DataObject();
+
+                bitmpa.Save(pngMemStream, ImageFormat.Png);
+                data.SetData("PNG", pngMemStream, false);
+
+                Clipboard.SetDataObject(data, true);
+            }
+            catch { }
+        });
+        thread.SetApartmentState(ApartmentState.STA);
+        thread.Start(img);
+    }
+
+    private static Bitmap ToBitmap(this BitmapSource source)
+    {
+        using (var outStream = new MemoryStream())
+        {
+            BitmapEncoder enc = new PngBitmapEncoder();
+            enc.Frames.Add(BitmapFrame.Create(source));
+            enc.Save(outStream);
+            var bitmap = new Bitmap(outStream);
+
+            return new Bitmap(bitmap);
+        }
+    }
+}