Implement mania star difficulty calculation

osu.Game.Rulesets.Mania/Objects/ManiaHitObjectDifficulty.cs

@@ -0,0 +1,114 @@
+// Copyright (c) 2007-2018 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using osu.Game.Rulesets.Objects.Types;
+using System;
+
+namespace osu.Game.Rulesets.Mania.Objects
+{
+    class ManiaHitObjectDifficulty
+    {
+        /// <summary>
+        /// Factor by how much individual / overall strain decays per second.
+        /// </summary>
+        /// <remarks>
+        /// These values are results of tweaking a lot and taking into account general feedback.
+        /// </remarks>
+        internal const double INDIVIDUAL_DECAY_BASE = 0.125;
+        internal const double OVERALL_DECAY_BASE = 0.30;
+
+        internal ManiaHitObject BaseHitObject;
+
+        private int beatmapColumnCount;
+
+
+        private double endTime;
+        private double[] heldUntil;
+
+        /// <summary>
+        ///  Measures jacks or more generally: repeated presses of the same button
+        /// </summary>
+        private double[] individualStrains;
+
+        internal double IndividualStrain
+        {
+            get
+            {
+                return individualStrains[BaseHitObject.Column];
+            }
+
+            set
+            {
+                individualStrains[BaseHitObject.Column] = value;
+            }
+        }
+
+        /// <summary>
+        /// Measures note density in a way
+        /// </summary>
+        internal double OverallStrain = 1;
+
+        public ManiaHitObjectDifficulty(ManiaHitObject baseHitObject, int columnCount)
+        {
+            BaseHitObject = baseHitObject;
+
+            endTime = (baseHitObject as IHasEndTime)?.EndTime ?? baseHitObject.StartTime;
+
+            beatmapColumnCount = columnCount;
+            heldUntil = new double[beatmapColumnCount];
+            individualStrains = new double[beatmapColumnCount];
+
+            for (int i = 0; i < beatmapColumnCount; ++i)
+            {
+                individualStrains[i] = 0;
+                heldUntil[i] = 0;
+            }
+        }
+
+        internal void CalculateStrains(ManiaHitObjectDifficulty previousHitObject, double timeRate)
+        {
+            // TODO: Factor in holds
+            double addition = 1.0;
+            double timeElapsed = (BaseHitObject.StartTime - previousHitObject.BaseHitObject.StartTime) / timeRate;
+            double individualDecay = Math.Pow(INDIVIDUAL_DECAY_BASE, timeElapsed / 1000);
+            double overallDecay = Math.Pow(OVERALL_DECAY_BASE, timeElapsed / 1000);
+
+            double holdFactor = 1.0; // Factor to all additional strains in case something else is held
+            double holdAddition = 0; // Addition to the current note in case it's a hold and has to be released awkwardly
+
+            // Fill up the heldUntil array
+            for (int i = 0; i < beatmapColumnCount; ++i)
+            {
+                heldUntil[i] = previousHitObject.heldUntil[i];
+
+                // If there is at least one other overlapping end or note, then we get an addition, buuuuuut...
+                if (BaseHitObject.StartTime < heldUntil[i] && endTime > heldUntil[i])
+                {
+                    holdAddition = 1.0;
+                }
+
+                // ... this addition only is valid if there is _no_ other note with the same ending. Releasing multiple notes at the same time is just as easy as releasing 1
+                if (endTime == heldUntil[i])
+                {
+                    holdAddition = 0;
+                }
+
+                // We give a slight bonus to everything if something is held meanwhile
+                if (heldUntil[i] > endTime)
+                {
+                    holdFactor = 1.25;
+                }
+
+                // Decay individual strains
+                individualStrains[i] = previousHitObject.individualStrains[i] * individualDecay;
+            }
+
+            heldUntil[BaseHitObject.Column] = endTime;
+
+            // Increase individual strain in own column
+            IndividualStrain += (2.0/* + (double)SpeedMania.Column / 8.0*/) * holdFactor;
+
+            OverallStrain = previousHitObject.OverallStrain * overallDecay + (addition + holdAddition) * holdFactor;
+        }
+    }
+}