maintain old rhythm data for display

osu.Game.Rulesets.Taiko/Difficulty/Preprocessing/Rhythm/TaikoDifficultyHitObjectRhythm.cs

@@ -1,24 +1,82 @@
 // Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
+using System;
+using System.Linq;
+using osu.Game.Rulesets.Taiko.Difficulty.Preprocessing.Rhythm.Data;
+
 namespace osu.Game.Rulesets.Taiko.Difficulty.Preprocessing.Rhythm
 {
     /// <summary>
-    /// Represents a rhythm change in a taiko map.
+    /// Stores rhythm data for a <see cref="TaikoDifficultyHitObject"/>.
     /// </summary>
     public class TaikoDifficultyHitObjectRhythm
     {
+        /// <summary>
+        /// The group of hit objects with consistent rhythm that this object belongs to.
+        /// </summary>
+        public EvenHitObjects? EvenHitObjects;
+
+        /// <summary>
+        /// The larger pattern of rhythm groups that this object is part of.
+        /// </summary>
+        public EvenPatterns? EvenPatterns;
+
+        /// <summary>
+        /// The ratio of current <see cref="Rulesets.Difficulty.Preprocessing.DifficultyHitObject.DeltaTime"/>
+        /// to previous <see cref="Rulesets.Difficulty.Preprocessing.DifficultyHitObject.DeltaTime"/> for the rhythm change.
+        /// A <see cref="Ratio"/> above 1 indicates a slow-down; a <see cref="Ratio"/> below 1 indicates a speed-up.
+        /// </summary>
+        public readonly double Ratio;
+
         /// <summary>
         /// The difficulty multiplier associated with this rhythm change.
         /// </summary>
         public readonly double Difficulty;
 
         /// <summary>
-        /// The ratio of current <see cref="osu.Game.Rulesets.Difficulty.Preprocessing.DifficultyHitObject.DeltaTime"/>
+        /// List of most common rhythm changes in taiko maps. This is used as a display value.
-        /// to previous <see cref="osu.Game.Rulesets.Difficulty.Preprocessing.DifficultyHitObject.DeltaTime"/> for the rhythm change.
-        /// A <see cref="Ratio"/> above 1 indicates a slow-down; a <see cref="Ratio"/> below 1 indicates a speed-up.
         /// </summary>
-        public readonly double Ratio;
+        /// <remarks>
+        /// The general guidelines for the values are:
+        /// <list type="bullet">
+        /// <item>rhythm changes with ratio closer to 1 (that are <i>not</i> 1) are harder to play,</item>
+        /// <item>speeding up is <i>generally</i> harder than slowing down (with exceptions of rhythm changes requiring a hand switch).</item>
+        /// </list>
+        /// </remarks>
+        private static readonly TaikoDifficultyHitObjectRhythm[] common_rhythms =
+        {
+            new TaikoDifficultyHitObjectRhythm(1, 1, 0.0),
+            new TaikoDifficultyHitObjectRhythm(2, 1, 0.3),
+            new TaikoDifficultyHitObjectRhythm(1, 2, 0.5),
+            new TaikoDifficultyHitObjectRhythm(3, 1, 0.3),
+            new TaikoDifficultyHitObjectRhythm(1, 3, 0.35),
+            new TaikoDifficultyHitObjectRhythm(3, 2, 0.6),
+            new TaikoDifficultyHitObjectRhythm(2, 3, 0.4),
+            new TaikoDifficultyHitObjectRhythm(5, 4, 0.5),
+            new TaikoDifficultyHitObjectRhythm(4, 5, 0.7)
+        };
+
+        /// <summary>
+        /// Initialises a new instance of <see cref="TaikoDifficultyHitObjectRhythm"/>s,
+        /// calculating the closest rhythm change and its associated difficulty for the current hit object.
+        /// </summary>
+        /// <param name="current">The current <see cref="TaikoDifficultyHitObject"/> being processed.</param>
+        public TaikoDifficultyHitObjectRhythm(TaikoDifficultyHitObject current)
+        {
+            var previous = current.Previous(0);
+
+            if (previous == null)
+            {
+                Ratio = 1;
+                Difficulty = 0.0;
+                return;
+            }
+
+            TaikoDifficultyHitObjectRhythm closestRhythm = getClosestRhythm(current.DeltaTime, previous.DeltaTime);
+            Ratio = closestRhythm.Ratio;
+            Difficulty = closestRhythm.Difficulty;
+        }
 
         /// <summary>
         /// Creates an object representing a rhythm change.
@@ -26,10 +84,24 @@ namespace osu.Game.Rulesets.Taiko.Difficulty.Preprocessing.Rhythm
         /// <param name="numerator">The numerator for <see cref="Ratio"/>.</param>
         /// <param name="denominator">The denominator for <see cref="Ratio"/></param>
         /// <param name="difficulty">The difficulty multiplier associated with this rhythm change.</param>
-        public TaikoDifficultyHitObjectRhythm(int numerator, int denominator, double difficulty)
+        private TaikoDifficultyHitObjectRhythm(int numerator, int denominator, double difficulty)
         {
             Ratio = numerator / (double)denominator;
             Difficulty = difficulty;
         }
+
+        /// <summary>
+        /// Determines the closest rhythm change from <see cref="common_rhythms"/> that matches the timing ratio
+        /// between the current and previous intervals.
+        /// </summary>
+        /// <param name="currentDeltaTime">The time difference between the current hit object and the previous one.</param>
+        /// <param name="previousDeltaTime">The time difference between the previous hit object and the one before it.</param>
+        /// <returns>The closest matching rhythm from <see cref="common_rhythms"/>.</returns>
+        private TaikoDifficultyHitObjectRhythm getClosestRhythm(double currentDeltaTime, double previousDeltaTime)
+        {
+            double ratio = currentDeltaTime / previousDeltaTime;
+            return common_rhythms.OrderBy(x => Math.Abs(x.Ratio - ratio)).First();
+        }
     }
 }
+