Update MathUtilities.cs

src/Avalonia.Base/Utilities/MathUtilities.cs

@@ -1,6 +1,9 @@
 // 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 System.Runtime.InteropServices;
+
 namespace Avalonia.Utilities
 {
     /// <summary>
@@ -8,6 +11,86 @@ namespace Avalonia.Utilities
     /// </summary>
     public static class MathUtilities
     {
+        /// <summary>
+        /// AreClose - Returns whether or not two doubles are "close".  That is, whether or 
+        /// not they are within epsilon of each other.
+        /// </summary> 
+        /// <param name="value1"> The first double to compare. </param>
+        /// <param name="value2"> The second double to compare. </param>
+        public static bool AreClose(double value1, double value2)
+        {
+            //in case they are Infinities (then epsilon check does not work)
+            if (value1 == value2) return true;
+            double eps = (Math.Abs(value1) + Math.Abs(value2) + 10.0) * double.Epsilon;
+            double delta = value1 - value2;
+            return (-eps < delta) && (eps > delta);
+        }
+
+        /// <summary>
+        /// LessThan - Returns whether or not the first double is less than the second double.
+        /// That is, whether or not the first is strictly less than *and* not within epsilon of
+        /// the other number.
+        /// <param name="value1"> The first double to compare. </param>
+        /// <param name="value2"> The second double to compare. </param>
+        public static bool LessThan(double value1, double value2)
+        {
+            return (value1 < value2) && !AreClose(value1, value2);
+        }
+
+        /// <summary>
+        /// GreaterThan - Returns whether or not the first double is greater than the second double.
+        /// That is, whether or not the first is strictly greater than *and* not within epsilon of
+        /// the other number.
+        /// <param name="value1"> The first double to compare. </param>
+        /// <param name="value2"> The second double to compare. </param>
+        public static bool GreaterThan(double value1, double value2)
+        {
+            return (value1 > value2) && !AreClose(value1, value2);
+        }
+
+        /// <summary>
+        /// LessThanOrClose - Returns whether or not the first double is less than or close to
+        /// the second double.  That is, whether or not the first is strictly less than or within
+        /// epsilon of the other number.
+        /// <param name="value1"> The first double to compare. </param>
+        /// <param name="value2"> The second double to compare. </param>
+        public static bool LessThanOrClose(double value1, double value2)
+        {
+            return (value1 < value2) || AreClose(value1, value2);
+        }
+
+        /// <summary>
+        /// GreaterThanOrClose - Returns whether or not the first double is greater than or close to
+        /// the second double.  That is, whether or not the first is strictly greater than or within
+        /// epsilon of the other number.
+        /// </summary>
+        /// <param name="value1"> The first double to compare. </param>
+        /// <param name="value2"> The second double to compare. </param>
+        public static bool GreaterThanOrClose(double value1, double value2)
+        {
+            return (value1 > value2) || AreClose(value1, value2);
+        }
+
+        /// <summary>
+        /// IsOne - Returns whether or not the double is "close" to 1.  Same as AreClose(double, 1),
+        /// but this is faster.
+        /// </summary>
+        /// <param name="value"> The double to compare to 1. </param>
+        public static bool IsOne(double value)
+        {
+            return Math.Abs(value - 1.0) < 10.0 * double.Epsilon;
+        }
+
+        /// <summary>
+        /// IsZero - Returns whether or not the double is "close" to 0.  Same as AreClose(double, 0),
+        /// but this is faster.
+        /// </summary>
+        /// <param name="value"> The double to compare to 0. </param>
+        public static bool IsZero(double value)
+        {
+            return Math.Abs(value) < 10.0 * double.Epsilon;
+        }
+
         /// <summary>
         /// Clamps a value between a minimum and maximum value.
         /// </summary>
@@ -31,6 +114,39 @@ namespace Avalonia.Utilities
             }
         }
 
+        /// <summary>
+        /// Calculates the value to be used for layout rounding at high DPI.
+        /// </summary>
+        /// <param name="value">Input value to be rounded.</param>
+        /// <param name="dpiScale">Ratio of screen's DPI to layout DPI</param>
+        /// <returns>Adjusted value that will produce layout rounding on screen at high dpi.</returns>
+        /// <remarks>This is a layout helper method. It takes DPI into account and also does not return
+        /// the rounded value if it is unacceptable for layout, e.g. Infinity or NaN. It's a helper associated with
+        /// UseLayoutRounding  property and should not be used as a general rounding utility.</remarks>
+        public static double RoundLayoutValue(double value, double dpiScale)
+        {
+            double newValue;
+
+            // If DPI == 1, don't use DPI-aware rounding.
+            if (!MathUtilities.AreClose(dpiScale, 1.0))
+            {
+                newValue = Math.Round(value * dpiScale) / dpiScale;
+                // If rounding produces a value unacceptable to layout (NaN, Infinity or MaxValue), use the original value.
+                if (double.IsNaN(newValue) ||
+                    double.IsInfinity(newValue) ||
+                    MathUtilities.AreClose(newValue, double.MaxValue))
+                {
+                    newValue = value;
+                }
+            }
+            else
+            {
+                newValue = Math.Round(value);
+            }
+
+            return newValue;
+        }
+
         /// <summary>
         /// Clamps a value between a minimum and maximum value.
         /// </summary>
@@ -54,4 +170,4 @@ namespace Avalonia.Utilities
             }
         }
     }
-}
+}