osu/osu.Game/Rulesets/UI/HitObjectContainer.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.Collections.Generic;
using System.Linq;
using osu.Framework.Graphics;
using osu.Framework.Graphics.Containers;
using osu.Game.Rulesets.Objects.Drawables;

namespace osu.Game.Rulesets.UI
{
    public class HitObjectContainer : LifetimeManagementContainer
    {
        public IEnumerable<DrawableHitObject> Objects => InternalChildren.Cast<DrawableHitObject>().OrderBy(h => h.HitObject.StartTime);
        public IEnumerable<DrawableHitObject> AliveObjects => AliveInternalChildren.Cast<DrawableHitObject>().OrderBy(h => h.HitObject.StartTime);

        public HitObjectContainer()
        {
            RelativeSizeAxes = Axes.Both;
        }

        public virtual void Add(DrawableHitObject hitObject) => AddInternal(hitObject);
        public virtual bool Remove(DrawableHitObject hitObject) => RemoveInternal(hitObject);

        protected override int Compare(Drawable x, Drawable y)
        {
            if (!(x is DrawableHitObject xObj) || !(y is DrawableHitObject yObj))
                return base.Compare(x, y);

            // Put earlier hitobjects towards the end of the list, so they handle input first
            int i = yObj.HitObject.StartTime.CompareTo(xObj.HitObject.StartTime);
            return i == 0 ? CompareReverseChildID(x, y) : i;
        }

        protected override void OnChildLifetimeBoundaryCrossed(LifetimeBoundaryCrossedEvent e)
        {
            if (e.Kind == LifetimeBoundaryKind.End && e.Direction == LifetimeBoundaryCrossingDirection.Forward && e.Child is DrawableHitObject hitObject)
                hitObject.OnLifetimeEnd();
        }
    }
}