refactor mirror engine

src/Avalonia.Controls/Control.cs

@@ -67,17 +67,10 @@ namespace Avalonia.Controls
         /// </summary>
         public static readonly AttachedProperty<FlowDirection> FlowDirectionProperty =
             AvaloniaProperty.RegisterAttached<Control, Control, FlowDirection>(nameof(FlowDirection), inherits: true);
-
-        /// <summary>
-        /// Defines the <see cref="RenderTransform"/> property.
-        /// </summary>
-        public static new readonly StyledProperty<ITransform?> RenderTransformProperty =
-            Visual.RenderTransformProperty.AddOwner<Control>();
     
         private DataTemplates? _dataTemplates;
         private IControl? _focusAdorner;
         private AutomationPeer? _automationPeer;
-        private bool _hasMirrorTransform;
 
         /// <summary>
         /// Gets or sets the control's focus adorner.
@@ -133,28 +126,6 @@ namespace Avalonia.Controls
             set => SetValue(FlowDirectionProperty, value);
         }
 
-        /// <inheritdoc/>
-        public override ITransform? RenderTransform 
-        { 
-            get => base.RenderTransform;
-            set
-            {
-                if (_hasMirrorTransform)
-                {
-                    if (value == null)
-                    {
-                        value = MirrorTrasform();
-                    }
-                    else
-                    {
-                        value = MirrorTrasform().MergeTransforms(value);
-                    }
-                }
-
-                base.RenderTransform = value; 
-            }
-        }
-
         /// <summary>
         /// Occurs when the user has completed a context input gesture, such as a right-click.
         /// </summary>
@@ -375,13 +346,15 @@ namespace Avalonia.Controls
 
             bool shouldApplyMirrorTransform = thisShouldGetMirrored != parentShouldGetMirrored;
 
+            if (this is IRenderRoot) shouldApplyMirrorTransform = false;
+
             if (shouldApplyMirrorTransform)
             {
-                AddMirrorTransform();
+                IsMirrorTransform = true;
             }
             else
             {
-                RemoveMirrorTransform();
+                IsMirrorTransform = false;
             }
         }
 
@@ -396,57 +369,15 @@ namespace Avalonia.Controls
             }
         }
 
-        private void AddMirrorTransform()
-        {
-            if (_hasMirrorTransform)
-            {
-                return;
-            }
-
-            var mirrorTransform = MirrorTrasform();
-            var renderTransform = RenderTransform;
-
-            ITransform? finalTransform = mirrorTransform;
-            if (renderTransform != null)
-            {
-                finalTransform = mirrorTransform.MergeTransforms(renderTransform);
-            }
-
-            base.RenderTransform = finalTransform;
-            _hasMirrorTransform = true;
-        }
-
-        private void RemoveMirrorTransform()
-        {
-            if (!_hasMirrorTransform)
-            {
-                return;
-            }
-
-            ITransform mirrorTransform = MirrorTrasform();
-            ITransform renderTransform = RenderTransform!;
-            
-            ITransform? finalTransform = mirrorTransform.MergeTransforms(renderTransform);
-            if (finalTransform!.Value == Matrix.Identity)
-            {
-                finalTransform = null;
-            }
-
-            _hasMirrorTransform = false;
-            base.RenderTransform = finalTransform;
-        }
-
-
         /// <summary>
-        /// Determines whether the element should be presented mirrored
-        /// if FlowDirection is RightToLeft
+        /// Determines whether the element should be presented mirrored, this
+        /// method related to FlowDirection system and as return true if FlowDirection
+        /// is RightToLeft. For controls that want to avoid this behavior, it is 
+        /// possible to override this method and return false. 
         /// </summary>
         protected virtual bool ShouldPresentedMirrored()
         {
             return FlowDirection == FlowDirection.RightToLeft;
         }
-
-        static ITransform MirrorTrasform() => 
-            new MatrixTransform(new Avalonia.Matrix(-1, 0, 0, 1, 0.0, 0.0));
     }
 }

src/Avalonia.Visuals/ApiCompatBaseline.txt

@@ -176,5 +176,6 @@ InterfacesShouldHaveSameMembers : Interface member 'public Avalonia.Media.GlyphR
 MembersMustExist : Member 'public Avalonia.Media.GlyphRun Avalonia.Platform.ITextShaperImpl.ShapeText(Avalonia.Utilities.ReadOnlySlice<System.Char>, Avalonia.Media.Typeface, System.Double, System.Globalization.CultureInfo)' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'protected void Avalonia.Rendering.RendererBase.RenderFps(Avalonia.Platform.IDrawingContextImpl, Avalonia.Rect, System.Nullable<System.Int32>)' does not exist in the implementation but it does exist in the contract.
 MembersMustExist : Member 'public void Avalonia.Utilities.ReadOnlySlice<T>..ctor(System.ReadOnlyMemory<T>, System.Int32, System.Int32)' does not exist in the implementation but it does exist in the contract.
-CannotRemoveBaseTypeOrInterface : Type 'Avalonia.Media.Transforms' does not inherit from base type 'Avalonia.Collections.AvaloniaList<Avalonia.Media.Transform>' in the implementation but it does in the contract.
-Total Issues: 178
+InterfacesShouldHaveSameMembers : Interface member 'public System.Boolean Avalonia.VisualTree.IVisual.IsMirrorTransform' is present in the implementation but not in the contract.
+InterfacesShouldHaveSameMembers : Interface member 'public System.Boolean Avalonia.VisualTree.IVisual.IsMirrorTransform.get()' is present in the implementation but not in the contract.
+Total Issues: 179

src/Avalonia.Visuals/Media/TransformExtensions.cs

@@ -22,23 +22,5 @@ namespace Avalonia.Media
 
             return (transform as Transform)?.ToImmutable() ?? new ImmutableTransform(transform.Value);
         }
-
-        /// <summary>
-        /// Merge two transforms to an one transform.
-        /// </summary>
-        /// <param name="srcTransform">The original transform.</param>
-        /// <param name="additionalTransform">The additional transform to be added.</param>
-        /// <returns>
-        /// One ITransform that includes both.
-        /// </returns>
-        public static ITransform MergeTransforms(this ITransform srcTransform, ITransform additionalTransform)
-        {
-            TransformGroup groupTransform = new TransformGroup();
-
-            groupTransform.Children.Add(srcTransform);
-            groupTransform.Children.Add(additionalTransform);
-
-            return groupTransform;
-        }
     }
 }

src/Avalonia.Visuals/Media/TransformGroup.cs

@@ -18,20 +18,8 @@ namespace Avalonia.Media
             Children.CollectionChanged += delegate
             {
                 Children.ForEachItem(
-                    (tr) => 
-                    {
-                        if (tr is IMutableTransform mutTr)
-                        {
-                            mutTr.Changed += ChildTransform_Changed;
-                        }
-                    },
-                    (tr) => 
-                    {
-                        if (tr is IMutableTransform mutTr)
-                        {
-                            mutTr.Changed -= ChildTransform_Changed;
-                        }
-                    },
+                    (tr) => tr.Changed += ChildTransform_Changed,
+                    (tr) => tr.Changed -= ChildTransform_Changed,
                     () => { });
             };
         }
@@ -73,7 +61,7 @@ namespace Avalonia.Media
         }
     }
 
-    public sealed class Transforms : AvaloniaList<ITransform>
+    public sealed class Transforms : AvaloniaList<Transform>
     {
     }
 }

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

@@ -195,6 +195,12 @@ namespace Avalonia.Rendering.SceneGraph
                     renderTransform = (-offset) * visual.RenderTransform.Value * (offset);
                 }
 
+                if (visual.IsMirrorTransform)
+                {
+                    var mirrorMatrix = new Matrix(-1.0, 0.0, 0.0, 1.0, visual.Bounds.Width, 0);
+                    renderTransform *= mirrorMatrix;
+                }
+
                 m = renderTransform * m;
 
                 using (contextImpl.BeginUpdate(node))

src/Avalonia.Visuals/Visual.cs

@@ -68,6 +68,12 @@ namespace Avalonia
         public static readonly StyledProperty<IBrush?> OpacityMaskProperty =
             AvaloniaProperty.Register<Visual, IBrush?>(nameof(OpacityMask));
 
+        /// <summary>
+        /// Defines the <see cref="IsMirrorTransform"/> property.
+        /// </summary>
+        public static readonly DirectProperty<Visual, bool> IsMirrorTransformProperty =
+            AvaloniaProperty.RegisterDirect<Visual, bool>(nameof(IsMirrorTransform), o => o.IsMirrorTransform);
+
         /// <summary>
         /// Defines the <see cref="RenderTransform"/> property.
         /// </summary>
@@ -96,6 +102,7 @@ namespace Avalonia
         private TransformedBounds? _transformedBounds;
         private IRenderRoot? _visualRoot;
         private IVisual? _visualParent;
+        private bool _isMirrorTransform;
 
         /// <summary>
         /// Initializes static members of the <see cref="Visual"/> class.
@@ -107,7 +114,8 @@ namespace Avalonia
                 ClipProperty,
                 ClipToBoundsProperty,
                 IsVisibleProperty,
-                OpacityProperty);
+                OpacityProperty,
+                IsMirrorTransformProperty);
             RenderTransformProperty.Changed.Subscribe(RenderTransformChanged);
             ZIndexProperty.Changed.Subscribe(ZIndexChanged);
         }
@@ -119,7 +127,7 @@ namespace Avalonia
         {
             // Disable transitions until we're added to the visual tree.
             DisableTransitions();
-
+            
             var visualChildren = new AvaloniaList<IVisual>();
             visualChildren.ResetBehavior = ResetBehavior.Remove;
             visualChildren.Validate = visual => ValidateVisualChild(visual);
@@ -219,10 +227,19 @@ namespace Avalonia
             set { SetValue(OpacityMaskProperty, value); }
         }
 
+        /// <summary>
+        /// Gets or sets a value indicating whether this control presented as mirror.
+        /// </summary>
+        public bool IsMirrorTransform 
+        { 
+            get { return _isMirrorTransform; }
+            protected set { SetAndRaise(IsMirrorTransformProperty, ref _isMirrorTransform, value); }
+        }
+
         /// <summary>
         /// Gets or sets the render transform of the control.
         /// </summary>
-        public virtual ITransform? RenderTransform
+        public ITransform? RenderTransform
         {
             get { return GetValue(RenderTransformProperty); }
             set { SetValue(RenderTransformProperty, value); }

src/Avalonia.Visuals/VisualExtensions.cs

@@ -110,6 +110,12 @@ namespace Avalonia
                     result *= renderTransform;
                 }
 
+                if (v.IsMirrorTransform)
+                {
+                    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.Visuals/VisualTree/IVisual.cs

@@ -75,6 +75,11 @@ namespace Avalonia.VisualTree
         /// </summary>
         IBrush? OpacityMask { get; set; }
 
+        /// <summary>
+        /// Gets a value indicating whether this control presented as mirror.
+        /// </summary>
+        bool IsMirrorTransform { get; }
+
         /// <summary>
         /// Gets or sets the render transform of the control.
         /// </summary>