Added SkewTransform and the corresponding skew function in Matrix class.

src/Avalonia.Visuals/Matrix.cs

@@ -150,6 +150,19 @@ namespace Avalonia
             return new Matrix(cos, sin, -sin, cos, 0, 0);
         }
 
+        /// <summary>
+        /// Creates a skew matrix from the given axis skew angles in radians.
+        /// </summary>
+        /// <param name="xAngle">The amount of skew along the X-axis, in radians.</param>
+        /// <param name="yAngle">The amount of skew along the Y-axis, in radians.</param>
+        /// <returns>A rotation matrix.</returns>
+        public static Matrix CreateSkew(double xAngle, double yAngle)
+        {
+            double tanX = Math.Tan(xAngle);
+            double tanY = Math.Tan(yAngle);
+            return new Matrix(1.0, tanX, tanY, 1.0, 0.0, 0.0);
+        }
+
         /// <summary>
         /// Creates a scale matrix from the given X and Y components.
         /// </summary>
@@ -215,7 +228,6 @@ namespace Avalonia
             return (_m11 * _m22) - (_m12 * _m21);
         }
 
-
         /// <summary>
         /// Returns a boolean indicating whether the matrix is equal to the other given matrix.
         /// </summary>

src/Avalonia.Visuals/Media/SkewTransform.cs

@@ -0,0 +1,69 @@
+// Copyright (c) The Avalonia Project. All rights reserved.
+// Licensed under the MIT license. See licence.md file in the project root for full license information.
+
+using System;
+using Avalonia.VisualTree;
+
+namespace Avalonia.Media
+{
+    /// <summary>
+    /// Skews an <see cref="IVisual"/>.
+    /// </summary>
+    public class SkewTransform : Transform
+    {
+        /// <summary>
+        /// Defines the <see cref="AngleX"/> property.
+        /// </summary>
+        public static readonly StyledProperty<double> AngleXProperty =
+                    AvaloniaProperty.Register<SkewTransform, double>(nameof(AngleX));
+
+        /// <summary>
+        /// Defines the <see cref="AngleY"/> property.
+        /// </summary>
+        public static readonly StyledProperty<double> AngleYProperty =
+                    AvaloniaProperty.Register<SkewTransform, double>(nameof(AngleY));
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="SkewTransform"/> class.
+        /// </summary>
+        public SkewTransform()
+        {
+            this.GetObservable(AngleXProperty).Subscribe(_ => RaiseChanged());
+            this.GetObservable(AngleYProperty).Subscribe(_ => RaiseChanged());
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="SkewTransform"/> class.
+        /// </summary>
+        /// <param name="angleX">The skew angle of X-axis, in degrees.</param>
+        /// <param name="angleY">The skew angle of Y-axis, in degrees.</param>
+        public SkewTransform(double angleX, double angleY) : this()
+        {
+            AngleX = angleX;
+            AngleY = angleY;
+        }
+
+        /// <summary>
+        /// Gets or sets the AngleX property.
+        /// </summary>
+        public double AngleX
+        {
+            get { return GetValue(AngleXProperty); }
+            set { SetValue(AngleXProperty, value); }
+        }
+
+        /// <summary>
+        /// Gets or sets the AngleY property.
+        /// </summary>
+        public double AngleY
+        {
+            get { return GetValue(AngleYProperty); }
+            set { SetValue(AngleYProperty, value); }
+        }
+
+        /// <summary>
+        /// Gets the tranform's <see cref="Matrix"/>.
+        /// </summary>
+        public override Matrix Value => Matrix.CreateSkew(Matrix.ToRadians(AngleX), Matrix.ToRadians(AngleY));
+    }
+}