osu-lazer/osu.Game.Rulesets.Osu/Difficulty/Preprocessing/OsuDifficultyHitObject.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.Linq;
using osu.Game.Rulesets.Difficulty.Preprocessing;
using osu.Game.Rulesets.Objects;
using osu.Game.Rulesets.Osu.Objects;
using osuTK;

namespace osu.Game.Rulesets.Osu.Difficulty.Preprocessing
{
    public class OsuDifficultyHitObject : DifficultyHitObject
    {
        private const int normalized_radius = 52;

        protected new OsuHitObject BaseObject => (OsuHitObject)base.BaseObject;

        /// <summary>
        /// Milliseconds elapsed since the start time of the previous <see cref="OsuDifficultyHitObject"/>, with a minimum of 25ms to account for simultaneous <see cref="OsuDifficultyHitObject"/>s.
        /// </summary>
        public double StrainTime { get; private set; }

        /// <summary>
        /// Normalized distance from the end position of the previous <see cref="OsuDifficultyHitObject"/> to the start position of this <see cref="OsuDifficultyHitObject"/>.
        /// </summary>
        public double JumpDistance { get; private set; }

        /// <summary>
        /// Normalized distance between the start and end position of the previous <see cref="OsuDifficultyHitObject"/>.
        /// </summary>
        public double TravelDistance { get; private set; }

        /// <summary>
        /// Angle the player has to take to hit this <see cref="OsuDifficultyHitObject"/>.
        /// Calculated as the angle between the circles (current-2, current-1, current).
        /// </summary>
        public double? Angle { get; private set; }

        private readonly OsuHitObject lastLastObject;
        private readonly OsuHitObject lastObject;

        public OsuDifficultyHitObject(HitObject hitObject, HitObject lastLastObject, HitObject lastObject, double clockRate)
            : base(hitObject, lastObject, clockRate)
        {
            this.lastLastObject = (OsuHitObject)lastLastObject;
            this.lastObject = (OsuHitObject)lastObject;

            setDistances();

            // Capped to 25ms to prevent difficulty calculation breaking from simulatenous objects.
            StrainTime = Math.Max(DeltaTime, 25);
        }

        private void setDistances()
        {
            // We don't need to calculate either angle or distance when one of the last->curr objects is a spinner
            if (BaseObject is Spinner || lastObject is Spinner)
                return;

            // We will scale distances by this factor, so we can assume a uniform CircleSize among beatmaps.
            float scalingFactor = normalized_radius / (float)BaseObject.Radius;

            if (BaseObject.Radius < 30)
            {
                float smallCircleBonus = Math.Min(30 - (float)BaseObject.Radius, 5) / 50;
                scalingFactor *= 1 + smallCircleBonus;
            }

            if (lastObject is Slider lastSlider)
            {
                computeSliderCursorPosition(lastSlider);
                TravelDistance = lastSlider.LazyTravelDistance * scalingFactor;
            }

            Vector2 lastCursorPosition = getEndCursorPosition(lastObject);

            JumpDistance = (BaseObject.StackedPosition * scalingFactor - lastCursorPosition * scalingFactor).Length;

            if (lastLastObject != null && !(lastLastObject is Spinner))
            {
                Vector2 lastLastCursorPosition = getEndCursorPosition(lastLastObject);

                Vector2 v1 = lastLastCursorPosition - lastObject.StackedPosition;
                Vector2 v2 = BaseObject.StackedPosition - lastCursorPosition;

                float dot = Vector2.Dot(v1, v2);
                float det = v1.X * v2.Y - v1.Y * v2.X;

                Angle = Math.Abs(Math.Atan2(det, dot));
            }
        }

        private void computeSliderCursorPosition(Slider slider)
        {
            if (slider.LazyEndPosition != null)
                return;

            slider.LazyEndPosition = slider.StackedPosition;

            float approxFollowCircleRadius = (float)(slider.Radius * 3);
            var computeVertex = new Action<double>(t =>
            {
                double progress = (t - slider.StartTime) / slider.SpanDuration;
                if (progress % 2 >= 1)
                    progress = 1 - progress % 1;
                else
                    progress %= 1;

                // ReSharper disable once PossibleInvalidOperationException (bugged in current r# version)
                var diff = slider.StackedPosition + slider.Path.PositionAt(progress) - slider.LazyEndPosition.Value;
                float dist = diff.Length;

                if (dist > approxFollowCircleRadius)
                {
                    // The cursor would be outside the follow circle, we need to move it
                    diff.Normalize(); // Obtain direction of diff
                    dist -= approxFollowCircleRadius;
                    slider.LazyEndPosition += diff * dist;
                    slider.LazyTravelDistance += dist;
                }
            });

            // Skip the head circle
            var scoringTimes = slider.NestedHitObjects.Skip(1).Select(t => t.StartTime);
            foreach (var time in scoringTimes)
                computeVertex(time);
        }

        private Vector2 getEndCursorPosition(OsuHitObject hitObject)
        {
            Vector2 pos = hitObject.StackedPosition;

            if (hitObject is Slider slider)
            {
                computeSliderCursorPosition(slider);
                pos = slider.LazyEndPosition ?? pos;
            }

            return pos;
        }
    }
}