osu-lazer/osu.Game.Rulesets.Taiko/Difficulty/TaikoDifficultyCalculator.cs

// 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.Collections.Generic;
using System.Linq;
using osu.Game.Beatmaps;
using osu.Game.Rulesets.Difficulty;
using osu.Game.Rulesets.Difficulty.Preprocessing;
using osu.Game.Rulesets.Difficulty.Skills;
using osu.Game.Rulesets.Mods;
using osu.Game.Rulesets.Scoring;
using osu.Game.Rulesets.Taiko.Difficulty.Preprocessing;
using osu.Game.Rulesets.Taiko.Difficulty.Skills;
using osu.Game.Rulesets.Taiko.Mods;
using osu.Game.Rulesets.Taiko.Objects;
using osu.Game.Rulesets.Taiko.Scoring;

namespace osu.Game.Rulesets.Taiko.Difficulty
{
    public class TaikoDifficultyCalculator : DifficultyCalculator
    {
        private const double difficulty_multiplier = 1.9;

        public TaikoDifficultyCalculator(IRulesetInfo ruleset, IWorkingBeatmap beatmap)
            : base(ruleset, beatmap)
        {
        }

        protected override Skill[] CreateSkills(IBeatmap beatmap, Mod[] mods, double clockRate)
        {
            return new Skill[]
            {
                new Peaks(mods)
            };
        }

        protected override Mod[] DifficultyAdjustmentMods => new Mod[]
        {
            new TaikoModDoubleTime(),
            new TaikoModHalfTime(),
            new TaikoModEasy(),
            new TaikoModHardRock(),
        };

        protected override IEnumerable<DifficultyHitObject> CreateDifficultyHitObjects(IBeatmap beatmap, double clockRate)
        {
            List<DifficultyHitObject> difficultyHitObject = new List<DifficultyHitObject>();
            List<TaikoDifficultyHitObject> centreObjects = new List<TaikoDifficultyHitObject>();
            List<TaikoDifficultyHitObject> rimObjects = new List<TaikoDifficultyHitObject>();
            List<TaikoDifficultyHitObject> noteObjects = new List<TaikoDifficultyHitObject>();

            for (int i = 2; i < beatmap.HitObjects.Count; i++)
            {
                difficultyHitObject.Add(
                    new TaikoDifficultyHitObject(
                        beatmap.HitObjects[i], beatmap.HitObjects[i - 1], beatmap.HitObjects[i - 2], clockRate, difficultyHitObject,
                        centreObjects, rimObjects, noteObjects, difficultyHitObject.Count)
                );
            }

            // Find repetition interval for the final TaikoDifficultyHitObjectColour
            // TODO: Might be a good idea to refactor this
            ((TaikoDifficultyHitObject)difficultyHitObject.Last()).Colour?.FindRepetitionInterval();
            return difficultyHitObject;
        }

        protected override DifficultyAttributes CreateDifficultyAttributes(IBeatmap beatmap, Mod[] mods, Skill[] skills, double clockRate)
        {
            if (beatmap.HitObjects.Count == 0)
                return new TaikoDifficultyAttributes { Mods = mods };

            var combined = (Peaks)skills[0];

            double colourRating = Math.Sqrt(combined.ColourDifficultyValue * difficulty_multiplier);
            double rhythmRating = Math.Sqrt(combined.RhythmDifficultyValue * difficulty_multiplier);
            double staminaRating = Math.Sqrt(combined.StaminaDifficultyValue * difficulty_multiplier);

            double combinedRating = combined.DifficultyValue();
            double starRating = rescale(combinedRating * difficulty_multiplier);

            HitWindows hitWindows = new TaikoHitWindows();
            hitWindows.SetDifficulty(beatmap.Difficulty.OverallDifficulty);

            return new TaikoDifficultyAttributes
            {
                StarRating = starRating,
                Mods = mods,
                StaminaDifficulty = staminaRating,
                RhythmDifficulty = rhythmRating,
                ColourDifficulty = colourRating,
                PeakDifficulty = combinedRating,
                GreatHitWindow = hitWindows.WindowFor(HitResult.Great) / clockRate,
                MaxCombo = beatmap.HitObjects.Count(h => h is Hit),
            };
        }

        /// <summary>
        /// Applies a final re-scaling of the star rating to bring maps with recorded full combos below 9.5 stars.
        /// </summary>
        /// <param name="sr">The raw star rating value before re-scaling.</param>
        private double rescale(double sr)
        {
            if (sr < 0) return sr;

            return 10.43 * Math.Log(sr / 8 + 1);
        }
    }
}