diff --git a/src/Avalonia.Animation/KeySpline.cs b/src/Avalonia.Animation/KeySpline.cs
new file mode 100644
index 0000000000..34e8d89aae
--- /dev/null
+++ b/src/Avalonia.Animation/KeySpline.cs
@@ -0,0 +1,271 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+using System.Globalization;
+using System.Text;
+using Avalonia;
+using Avalonia.Utilities;
+
+// From: https://github.com/dotnet/wpf/blob/ae1790531c3b993b56eba8b1f0dd395a3ed7de75/src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/Animation/KeySpline.cs
+
+namespace Avalonia.Animation
+{
+    [TypeConverter(typeof(KeySplineTypeConverter))]
+    public class KeySpline : AvaloniaObject
+    {
+        // Control points
+        private double _controlPointX1;
+        private double _controlPointY1;
+        private double _controlPointX2;
+        private double _controlPointY2;
+        private bool _isSpecified;
+        private bool _isDirty;
+
+        // The parameter that corresponds to the most recent time
+        private double _parameter;
+
+        // Cached coefficients
+        private double _Bx;        // 3*points[0].X
+        private double _Cx;        // 3*points[1].X
+        private double _Cx_Bx;     // 2*(Cx - Bx)
+        private double _three_Cx;  // 3 - Cx
+
+        private double _By;        // 3*points[0].Y
+        private double _Cy;        // 3*points[1].Y
+
+        // constants
+        private const double _accuracy = .001;   // 1/3 the desired accuracy in X
+        private const double _fuzz = .000001;    // computational zero
+
+        public KeySpline()
+        {
+            _controlPointX1 = 0.0;
+            _controlPointY1 = 0.0;
+            _controlPointX2 = 1.0;
+            _controlPointY2 = 1.0;
+            _isDirty = true;
+        }
+
+        public KeySpline(double x1, double y1, double x2, double y2)
+        {
+            _controlPointX1 = x1;
+            _controlPointY1 = y1;
+            _controlPointX2 = x2;
+            _controlPointY2 = y2;
+            _isDirty = true;
+        }
+
+        public static KeySpline Parse(string value, CultureInfo culture)
+        {
+            using (var tokenizer = new StringTokenizer((string)value, CultureInfo.InvariantCulture, exceptionMessage: "Invalid KeySpline."))
+            {
+                return new KeySpline(tokenizer.ReadDouble(), tokenizer.ReadDouble(), tokenizer.ReadDouble(), tokenizer.ReadDouble());
+            }
+        }
+
+        public double ControlPointX1
+        {
+            get => _controlPointX1;
+            set => _controlPointX1 = value;
+        }
+
+        public double ControlPointY1
+        {
+            get => _controlPointY1;
+            set => _controlPointY1 = value;
+        }
+
+        public double ControlPointX2
+        {
+            get => _controlPointX2;
+            set => _controlPointX2 = value;
+        }
+
+        public double ControlPointY2
+        {
+            get => _controlPointY2;
+            set => _controlPointY2 = value;
+        }
+
+        /// <summary>
+        /// Calculates spline progress from a linear progress.
+        /// </summary>
+        /// <param name="linearProgress">the linear progress</param>
+        /// <returns>the spline progress</returns>
+        public double GetSplineProgress(double linearProgress)
+        {
+            //ReadPreamble();
+
+            if (_isDirty)
+            {
+                Build();
+            }
+
+            if (!_isSpecified)
+            {
+                return linearProgress;
+            }
+            else
+            {
+                SetParameterFromX(linearProgress);
+
+                return GetBezierValue(_By, _Cy, _parameter);
+            }
+        }
+
+        /// <summary>
+        /// Compute cached coefficients.
+        /// </summary>
+        private void Build()
+        {
+            if (_controlPointX1 == 0 && _controlPointY1 == 0 && _controlPointX2 == 1 && _controlPointY2 == 1)
+            {
+                // This KeySpline would have no effect on the progress.
+                _isSpecified = false;
+            }
+            else
+            {
+                _isSpecified = true;
+
+                _parameter = 0;
+
+                // X coefficients
+                _Bx = 3 * _controlPointX1;
+                _Cx = 3 * _controlPointX2;
+                _Cx_Bx = 2 * (_Cx - _Bx);
+                _three_Cx = 3 - _Cx;
+
+                // Y coefficients
+                _By = 3 * _controlPointY1;
+                _Cy = 3 * _controlPointY2;
+            }
+
+            _isDirty = false;
+        }
+
+        /// <summary>
+        /// Get an X or Y value with the Bezier formula.
+        /// </summary>
+        /// <param name="b">the second Bezier coefficient</param>
+        /// <param name="c">the third Bezier coefficient</param>
+        /// <param name="t">the parameter value to evaluate at</param>
+        /// <returns>the value of the Bezier function at the given parameter</returns>
+        static private double GetBezierValue(double b, double c, double t)
+        {
+            double s = 1.0 - t;
+            double t2 = t * t;
+
+            return b * t * s * s + c * t2 * s + t2 * t;
+        }
+
+        /// <summary>
+        /// Get X and dX/dt at a given parameter
+        /// </summary>
+        /// <param name="t">the parameter value to evaluate at</param>
+        /// <param name="x">the value of x there</param>
+        /// <param name="dx">the value of dx/dt there</param>
+        private void GetXAndDx(double t, out double x, out double dx)
+        {
+            double s = 1.0 - t;
+            double t2 = t * t;
+            double s2 = s * s;
+
+            x = _Bx * t * s2 + _Cx * t2 * s + t2 * t;
+            dx = _Bx * s2 + _Cx_Bx * s * t + _three_Cx * t2;
+        }
+
+        /// <summary>
+        /// Compute the parameter value that corresponds to a given X value, using a modified
+        /// clamped Newton-Raphson algorithm to solve the equation X(t) - time = 0. We make 
+        /// use of some known properties of this particular function:
+        /// * We are only interested in solutions in the interval [0,1]
+        /// * X(t) is increasing, so we can assume that if X(t) > time t > solution.  We use
+        ///   that to clamp down the search interval with every probe.
+        /// * The derivative of X and Y are between 0 and 3.
+        /// </summary>
+        /// <param name="time">the time, scaled to fit in [0,1]</param>
+        private void SetParameterFromX(double time)
+        {
+            // Dynamic search interval to clamp with
+            double bottom = 0;
+            double top = 1;
+
+            if (time == 0)
+            {
+                _parameter = 0;
+            }
+            else if (time == 1)
+            {
+                _parameter = 1;
+            }
+            else
+            {
+                // Loop while improving the guess
+                while (top - bottom > _fuzz)
+                {
+                    double x, dx, absdx;
+
+                    // Get x and dx/dt at the current parameter
+                    GetXAndDx(_parameter, out x, out dx);
+                    absdx = Math.Abs(dx);
+
+                    // Clamp down the search interval, relying on the monotonicity of X(t)
+                    if (x > time)
+                    {
+                        top = _parameter;      // because parameter > solution
+                    }
+                    else
+                    {
+                        bottom = _parameter;  // because parameter < solution
+                    }
+
+                    // The desired accuracy is in ultimately in y, not in x, so the
+                    // accuracy needs to be multiplied by dx/dy = (dx/dt) / (dy/dt).
+                    // But dy/dt <=3, so we omit that
+                    if (Math.Abs(x - time) < _accuracy * absdx)
+                    {
+                        break; // We're there
+                    }
+
+                    if (absdx > _fuzz)
+                    {
+                        // Nonzero derivative, use Newton-Raphson to obtain the next guess
+                        double next = _parameter - (x - time) / dx;
+
+                        // If next guess is out of the search interval then clamp it in
+                        if (next >= top)
+                        {
+                            _parameter = (_parameter + top) / 2;
+                        }
+                        else if (next <= bottom)
+                        {
+                            _parameter = (_parameter + bottom) / 2;
+                        }
+                        else
+                        {
+                            // Next guess is inside the search interval, accept it
+                            _parameter = next;
+                        }
+                    }
+                    else    // Zero derivative, halve the search interval
+                    {
+                        _parameter = (bottom + top) / 2;
+                    }
+                }
+            }
+        }
+    }
+
+    public class KeySplineTypeConverter : TypeConverter
+    {
+        public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
+        {
+            return sourceType == typeof(string);
+        }
+
+        public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
+        {
+            return KeySpline.Parse((string)value, culture);
+        }
+    }
+}