calculate mirrorTransform before renderTransform

src/Avalonia.Base/Rendering/ImmediateRenderer.cs

@@ -277,18 +277,20 @@ namespace Avalonia.Rendering
                 var m = Matrix.CreateTranslation(visual.Bounds.Position);
 
                 var renderTransform = Matrix.Identity;
+                
+                // this should be calculated BEFORE renderTransform
+                if (visual.HasMirrorTransform)
+                {
+                    var mirrorMatrix = new Matrix(-1.0, 0.0, 0.0, 1.0, visual.Bounds.Width, 0);
+                    renderTransform *= mirrorMatrix;
+                }
 
                 if (visual.RenderTransform != null)
                 {
                     var origin = visual.RenderTransformOrigin.ToPixels(new Size(visual.Bounds.Width, visual.Bounds.Height));
                     var offset = Matrix.CreateTranslation(origin);
-                    renderTransform = (-offset) * visual.RenderTransform.Value * (offset);
-                }
-
-                if (visual.HasMirrorTransform)
-                {
-                    var mirrorMatrix = new Matrix(-1.0, 0.0, 0.0, 1.0, visual.Bounds.Width, 0);
-                    renderTransform *= mirrorMatrix;
+                    var finalTransform = (-offset) * visual.RenderTransform.Value * (offset);
+                    renderTransform *= finalTransform;
                 }
 
                 m = renderTransform * m;

src/Avalonia.Base/Rendering/SceneGraph/SceneBuilder.cs

@@ -188,19 +188,21 @@ namespace Avalonia.Rendering.SceneGraph
 
                 var renderTransform = Matrix.Identity;
 
-                if (visual.RenderTransform != null)
-                {
-                    var origin = visual.RenderTransformOrigin.ToPixels(new Size(visual.Bounds.Width, visual.Bounds.Height));
-                    var offset = Matrix.CreateTranslation(origin);
-                    renderTransform = (-offset) * visual.RenderTransform.Value * (offset);
-                }
-
+                // this should be calculated BEFORE renderTransform
                 if (visual.HasMirrorTransform)
                 {
                     var mirrorMatrix = new Matrix(-1.0, 0.0, 0.0, 1.0, visual.Bounds.Width, 0);
                     renderTransform *= mirrorMatrix;
                 }
 
+                if (visual.RenderTransform != null)
+                {
+                    var origin = visual.RenderTransformOrigin.ToPixels(new Size(visual.Bounds.Width, visual.Bounds.Height));
+                    var offset = Matrix.CreateTranslation(origin);
+                    var finalTransform = (-offset) * visual.RenderTransform.Value * (offset);
+                    renderTransform *= finalTransform;
+                }
+
                 m = renderTransform * m;
 
                 using (contextImpl.BeginUpdate(node))

src/Avalonia.Base/VisualExtensions.cs

@@ -101,6 +101,13 @@ namespace Avalonia
 
             while (v != ancestor)
             {
+                // this should be calculated BEFORE renderTransform
+                if (v.HasMirrorTransform)
+                {
+                    var mirrorMatrix = new Matrix(-1.0, 0.0, 0.0, 1.0, v.Bounds.Width, 0);
+                    result *= mirrorMatrix;
+                }
+
                 if (v.RenderTransform?.Value != null)
                 {
                     var origin = v.RenderTransformOrigin.ToPixels(v.Bounds.Size);
@@ -110,12 +117,6 @@ namespace Avalonia
                     result *= renderTransform;
                 }
 
-                if (v.HasMirrorTransform)
-                {
-                    var mirrorMatrix = new Matrix(-1.0, 0.0, 0.0, 1.0, v.Bounds.Width, 0);
-                    result *= mirrorMatrix;
-                }
-
                 var topLeft = v.Bounds.TopLeft;
 
                 if (topLeft != default)

src/Avalonia.Controls/Viewbox.cs

@@ -1,7 +1,6 @@
 using Avalonia.Media;
 using Avalonia.Media.Immutable;
 using Avalonia.Metadata;
-using Avalonia.Layout;
 
 namespace Avalonia.Controls
 {
@@ -151,7 +150,7 @@ namespace Avalonia.Controls
         /// <summary>
         /// A simple container control which hosts its child as a visual but not logical child.
         /// </summary>
-        private class ViewboxContainer : Layoutable
+        private class ViewboxContainer : Control
         {
             private IControl? _child;