Gtk: Scale image buttons

NAPS2.Lib.Gtk/EtoForms/Gtk/GtkEtoPlatform.cs

@@ -38,6 +38,7 @@ public override IListView<T> CreateListView<T>(ListViewBehavior<T> behavior) =>
 
     public override void ConfigureImageButton(Button button, ButtonFlags flags)
     {
+        AttachDpiDependency(button, _ => button.ScaleImage());
     }
 
     public override Bitmap ToBitmap(IMemoryImage image)
@@ -269,10 +270,11 @@ public override Control AccessibleImageButton(Image image, string text, Action o
 
     public override void ConfigureZoomButton(Button button, string icon)
     {
+        var gtkButton = button.ToNative();
         button.Text = "";
-        button.Image = IconProvider.GetIcon(icon);
+        button.Image = IconProvider.GetIcon(icon, gtkButton.ScaleFactor);
+        button.ScaleImage();
         button.Size = Size.Empty;
-        var gtkButton = button.ToNative();
         gtkButton.StyleContext.AddClass("zoom-button");
         gtkButton.SetSizeRequest(0, 0);
     }

NAPS2.Lib.Gtk/Util/GtkEtoExtensions.cs

@@ -1,13 +1,50 @@
+using System.Reflection;
+using Eto.Forms;
+using Eto.GtkSharp;
+using Eto.GtkSharp.Forms.Controls;
 using Gdk;
 using Gtk;
 
 namespace NAPS2.Util;
 
 public static class GtkEtoExtensions
 {
+    private static readonly FieldInfo GtkImageField =
+        typeof(ButtonHandler<Gtk.Button, Eto.Forms.Button, Eto.Forms.Button.ICallback>).GetField("gtkimage",
+            BindingFlags.Instance | BindingFlags.NonPublic)!;
+
+    private static readonly MethodInfo SetImagePositionMethod =
+        typeof(ButtonHandler<Gtk.Button, Eto.Forms.Button, Eto.Forms.Button.ICallback>).GetMethod(
+            "SetImagePosition", BindingFlags.Instance | BindingFlags.NonPublic)!;
+
     public static Image ToScaledImage(this Pixbuf pixbuf, int scaleFactor)
     {
+        // Creating a Gtk.Image directly from a Pixbuf doesn't work if we want to render at high dpi.
+        // For example, if we have a 32x32 logical image size that actually gets rendered at 64x64 pixels due to a 2x
+        // display scaling, naively using the 64x64 image will get displayed with 64x64 logical size and 128x128
+        // physical size, which will look too big and blurry. To get an actual crisp image rendered at 32x32 logical
+        // pixels and 64x64 physical pixels, we first create a surface with a 2x scale factor and then create the
+        // Gtk.Image from that.
         var surface = Gdk.CairoHelper.SurfaceCreateFromPixbuf(pixbuf, scaleFactor, null);
         return new Image(surface);
     }
+
+    public static void SetImage(this Eto.Forms.Button button, Image image)
+    {
+        // Hack to inject a Gtk.Image directly into an Eto.Forms.Button. Normally Eto only takes an Eto.Drawing.Image
+        // (which wraps a Pixbuf) but to correctly scale images at high dpi we need a Gtk.Image constructed from a
+        // surface.
+        image.Show();
+        GtkImageField.SetValue(button.Handler, image);
+        SetImagePositionMethod.Invoke(button.Handler, []);
+    }
+
+    public static void ScaleImage(this Eto.Forms.Button button)
+    {
+        // Helper to read the Eto.Drawing.Image from the Eto.Forms.Button, scale it, then inject it back into the
+        // button.
+        int scaleFactor = button.ToNative().ScaleFactor;
+        var image = button.Image.ToGdk().ToScaledImage(scaleFactor);
+        button.SetImage(image);
+    }
 }