Added internal interface to get access to the NativeMagickImage class and use that in the Fx method of MagickImageCollection.

Author: dlemstra

src/Magick.NET/MagickImage.cs

@@ -2899,7 +2899,7 @@ public void Fx(string expression, Channels channels)
     {
         Throw.IfNullOrEmpty(nameof(expression), expression);
 
-        _nativeInstance.Instance = NativeMagickImage.Fx(_nativeInstance.Instance, expression, channels);
+        _nativeInstance.Instance = _nativeInstance.Fx(expression, channels);
     }
 
     /// <summary>
@@ -7047,12 +7047,6 @@ internal static IReadOnlyList<IMagickImage<QuantumType>> CreateList(IntPtr image
         return result;
     }
 
-    internal static IMagickImage<QuantumType> Fx(IMagickImage<QuantumType> image, string expression, Channels channels)
-    {
-        var result = NativeMagickImage.Fx(GetInstance(image), expression, channels);
-        return Create(result, GetSettings(image));
-    }
-
     internal static IntPtr GetInstance(IMagickImage? image)
     {
         if (image is null)
@@ -7064,6 +7058,14 @@ internal static IntPtr GetInstance(IMagickImage? image)
         throw new NotSupportedException();
     }
 
+    internal static INativeMagickImage GetNativeImage(IMagickImage image)
+    {
+        if (image is MagickImage magickImage)
+            return magickImage._nativeInstance;
+
+        throw new NotSupportedException();
+    }
+
     internal static MagickSettings GetSettings(IMagickImage<QuantumType> image)
     {
         if (image.Settings is MagickSettings settings)

src/Magick.NET/MagickImageCollection.cs

@@ -572,7 +572,9 @@ public IMagickImage<QuantumType> Fx(string expression, Channels channels)
         Throw.IfNullOrEmpty(nameof(expression), expression);
 
         using var imageAttacher = new TemporaryImageAttacher(_images);
-        return MagickImage.Fx(_images[0], expression, channels);
+        var nativeImage = MagickImage.GetNativeImage(_images[0]);
+        var newInstance = nativeImage.Fx(expression, channels);
+        return MagickImage.Create(newInstance, MagickImage.GetSettings(_images[0]));
     }
 
     /// <summary>

src/Magick.NET/Native/INativeMagickImage.cs

@@ -0,0 +1,12 @@
+// Copyright Dirk Lemstra https://github.com/dlemstra/Magick.NET.
+// Licensed under the Apache License, Version 2.0.
+
+using System;
+
+namespace ImageMagick
+{
+    internal interface INativeMagickImage
+    {
+        IntPtr Fx(string expression, Channels channels);
+    }
+}

src/Magick.NET/Native/MagickImage.cs

@@ -35,16 +35,12 @@ public partial class MagickImage : IDisposable
     private delegate long TellStreamDelegate(IntPtr user_data);
 
     [NativeInterop(RaiseWarnings = true, StaticDispose = true)]
-    private unsafe sealed partial class NativeMagickImage : NativeInstance
+    private unsafe sealed partial class NativeMagickImage : NativeInstance, INativeMagickImage
     {
         [Throws]
         [Cleanup(Name = nameof(DisposeInstance))]
         public static partial NativeMagickImage Create(IMagickSettings<QuantumType>? settings);
 
-        [Throws]
-        [Cleanup(Name = nameof(DisposeInstance))]
-        public static partial IntPtr Fx(IntPtr image, string expression, Channels channels);
-
         public static partial IntPtr GetNext(IntPtr image);
 
         public partial nuint AnimationDelay_Get();
@@ -463,6 +459,9 @@ private unsafe sealed partial class NativeMagickImage : NativeInstance
         [SetInstance]
         public partial void Frame(MagickRectangle geometry);
 
+        [Throws]
+        public partial IntPtr Fx(string expression, Channels channels);
+
         [Throws]
         public partial void GammaCorrect(double gamma, Channels channels);