From 19657cd00e461e4758ee6127edc61e2fa6f51b1f Mon Sep 17 00:00:00 2001
From: ekrctb <ekrctb@gmail.com>
Date: Thu, 22 Jul 2021 13:28:40 +0900
Subject: [PATCH] Guard against empty range in `PositionRange`

---
 osu.Game.Rulesets.Catch/Edit/PositionRange.cs | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/osu.Game.Rulesets.Catch/Edit/PositionRange.cs b/osu.Game.Rulesets.Catch/Edit/PositionRange.cs
index 543e773582..e61603e5e6 100644
--- a/osu.Game.Rulesets.Catch/Edit/PositionRange.cs
+++ b/osu.Game.Rulesets.Catch/Edit/PositionRange.cs
@@ -8,14 +8,15 @@ using System;
 namespace osu.Game.Rulesets.Catch.Edit
 {
     /// <summary>
-    /// Represents a closed interval of horizontal positions in the playfield.
+    /// Represents either the empty range or a closed interval of horizontal positions in the playfield.
+    /// A <see cref="PositionRange"/> represents a closed interval if it is <see cref="Min"/> &lt;= <see cref="Max"/>, and represents the empty range otherwise.
     /// </summary>
     public readonly struct PositionRange
     {
         public readonly float Min;
         public readonly float Max;
 
-        public float Length => Max - Min;
+        public float Length => Math.Max(0, Max - Min);
 
         public PositionRange(float value)
             : this(value, value)
@@ -30,7 +31,11 @@ namespace osu.Game.Rulesets.Catch.Edit
 
         public static PositionRange Union(PositionRange a, PositionRange b) => new PositionRange(Math.Min(a.Min, b.Min), Math.Max(a.Max, b.Max));
 
-        public float GetFlippedPosition(float x) => Max - (x - Min);
+        /// <summary>
+        /// Get the given position flipped (mirrored) for the axis at the center of this range.
+        /// Returns the given position unchanged if the range was empty.
+        /// </summary>
+        public float GetFlippedPosition(float x) => Min <= Max ? Max - (x - Min) : x;
 
         public static readonly PositionRange EMPTY = new PositionRange(float.PositiveInfinity, float.NegativeInfinity);
     }