osu-lazer/osu.Game/Rulesets/UI/Scrolling/ScrollingHitObjectContainer.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.Diagnostics;
using osu.Framework.Allocation;
using osu.Framework.Bindables;
using osu.Framework.Graphics;
using osu.Framework.Layout;
using osu.Game.Rulesets.Objects;
using osu.Game.Rulesets.Objects.Drawables;
using osu.Game.Rulesets.Objects.Types;
using osuTK;

namespace osu.Game.Rulesets.UI.Scrolling
{
    public class ScrollingHitObjectContainer : HitObjectContainer
    {
        private readonly IBindable<double> timeRange = new BindableDouble();
        private readonly IBindable<ScrollingDirection> direction = new Bindable<ScrollingDirection>();

        /// <summary>
        /// 0 for horizontal scroll, 1 for vertical scroll.
        /// </summary>
        private int scrollingAxis => direction.Value == ScrollingDirection.Left || direction.Value == ScrollingDirection.Right ? 0 : 1;

        /// <summary>
        /// A set of top-level <see cref="DrawableHitObject"/>s which have an up-to-date layout.
        /// </summary>
        private readonly HashSet<DrawableHitObject> layoutComputed = new HashSet<DrawableHitObject>();

        [Resolved]
        private IScrollingInfo scrollingInfo { get; set; }

        // Responds to changes in the layout. When the layout changes, all hit object states must be recomputed.
        private readonly LayoutValue layoutCache = new LayoutValue(Invalidation.RequiredParentSizeToFit | Invalidation.DrawInfo);

        public ScrollingHitObjectContainer()
        {
            RelativeSizeAxes = Axes.Both;

            AddLayout(layoutCache);
        }

        [BackgroundDependencyLoader]
        private void load()
        {
            direction.BindTo(scrollingInfo.Direction);
            timeRange.BindTo(scrollingInfo.TimeRange);

            direction.ValueChanged += _ => layoutCache.Invalidate();
            timeRange.ValueChanged += _ => layoutCache.Invalidate();
        }

        /// <summary>
        /// Given a position along the scrolling axis, return the time within this <see cref="HitObjectContainer"/>.
        /// </summary>
        /// <param name="position">The position along the scrolling axis.</param>
        /// <param name="referenceTime">The time the scrolling speed is used.</param>
        public double TimeAtPosition(float position, double referenceTime)
        {
            flipPositionIfRequired(ref position);
            return scrollingInfo.Algorithm.TimeAt(position, referenceTime, timeRange.Value, scrollLength);
        }

        /// <summary>
        /// Given a position in screen space, return the time within this <see cref="HitObjectContainer"/>.
        /// </summary>
        public double TimeAtScreenSpacePosition(Vector2 screenSpacePosition)
        {
            Vector2 localPosition = ToLocalSpace(screenSpacePosition);
            return TimeAtPosition(localPosition[scrollingAxis], Time.Current);
        }

        /// <summary>
        /// Given a time, return the position along the scrolling axis within this <see cref="HitObjectContainer"/> at time <paramref name="currentTime"/>.
        /// </summary>
        public float PositionAtTime(double time, double currentTime)
        {
            float pos = scrollingInfo.Algorithm.PositionAt(time, currentTime, timeRange.Value, scrollLength);
            flipPositionIfRequired(ref pos);
            return pos;
        }

        /// <summary>
        /// Given a time, return the position along the scrolling axis within this <see cref="HitObjectContainer"/> at the current time.
        /// </summary>
        public float PositionAtTime(double time) => PositionAtTime(time, Time.Current);

        /// <summary>
        /// Given a time, return the screen space position within this <see cref="HitObjectContainer"/>.
        /// In the non-scrolling axis, the center of this <see cref="HitObjectContainer"/> is returned.
        /// </summary>
        public Vector2 ScreenSpacePositionAtTime(double time)
        {
            float position = PositionAtTime(time, Time.Current);
            return scrollingAxis == 0
                ? ToScreenSpace(new Vector2(position, DrawHeight / 2))
                : ToScreenSpace(new Vector2(DrawWidth / 2, position));
        }

        /// <summary>
        /// Given a start time and end time of a scrolling object, return the length of the object along the scrolling axis.
        /// </summary>
        public float LengthAtTime(double startTime, double endTime)
        {
            return scrollingInfo.Algorithm.GetLength(startTime, endTime, timeRange.Value, scrollLength);
        }

        private float scrollLength => DrawSize[scrollingAxis];

        private void flipPositionIfRequired(ref float position)
        {
            // We're dealing with coordinates in which the position decreases towards the centre of the screen resulting in an increase in start time.
            // The scrolling algorithm instead assumes a top anchor meaning an increase in time corresponds to an increase in position,
            // so when scrolling downwards the coordinates need to be flipped.

            switch (scrollingInfo.Direction.Value)
            {
                case ScrollingDirection.Down:
                    position = DrawHeight - position;
                    break;

                case ScrollingDirection.Right:
                    position = DrawWidth - position;
                    break;
            }
        }

        protected override void AddDrawable(HitObjectLifetimeEntry entry, DrawableHitObject drawable)
        {
            base.AddDrawable(entry, drawable);

            invalidateHitObject(drawable);
            drawable.DefaultsApplied += invalidateHitObject;
        }

        protected override void RemoveDrawable(HitObjectLifetimeEntry entry, DrawableHitObject drawable)
        {
            base.RemoveDrawable(entry, drawable);

            drawable.DefaultsApplied -= invalidateHitObject;
            layoutComputed.Remove(drawable);
        }

        private void invalidateHitObject(DrawableHitObject hitObject)
        {
            hitObject.LifetimeStart = computeOriginAdjustedLifetimeStart(hitObject);
            layoutComputed.Remove(hitObject);
        }

        protected override void Update()
        {
            base.Update();

            if (layoutCache.IsValid) return;

            layoutComputed.Clear();

            // Reset lifetime to the conservative estimation.
            // If a drawable becomes alive by this lifetime, its lifetime will be updated to a more precise lifetime in the next update.
            foreach (var entry in Entries)
                entry.SetInitialLifetime();

            scrollingInfo.Algorithm.Reset();

            layoutCache.Validate();
        }

        protected override void UpdateAfterChildrenLife()
        {
            base.UpdateAfterChildrenLife();

            // We need to calculate hit object positions (including nested hit objects) as soon as possible after lifetimes
            // to prevent hit objects displayed in a wrong position for one frame.
            // Only AliveObjects need to be considered for layout (reduces overhead in the case of scroll speed changes).
            foreach (var obj in AliveObjects)
            {
                updatePosition(obj, Time.Current);

                if (layoutComputed.Contains(obj))
                    continue;

                updateLayoutRecursive(obj);

                layoutComputed.Add(obj);
            }
        }

        private double computeOriginAdjustedLifetimeStart(DrawableHitObject hitObject)
        {
            // Origin position may be relative to the parent size
            Debug.Assert(hitObject.Parent != null);

            float originAdjustment = 0.0f;

            // calculate the dimension of the part of the hitobject that should already be visible
            // when the hitobject origin first appears inside the scrolling container
            switch (direction.Value)
            {
                case ScrollingDirection.Up:
                    originAdjustment = hitObject.OriginPosition.Y;
                    break;

                case ScrollingDirection.Down:
                    originAdjustment = hitObject.DrawHeight - hitObject.OriginPosition.Y;
                    break;

                case ScrollingDirection.Left:
                    originAdjustment = hitObject.OriginPosition.X;
                    break;

                case ScrollingDirection.Right:
                    originAdjustment = hitObject.DrawWidth - hitObject.OriginPosition.X;
                    break;
            }

            return scrollingInfo.Algorithm.GetDisplayStartTime(hitObject.HitObject.StartTime, originAdjustment, timeRange.Value, scrollLength);
        }

        private void updateLayoutRecursive(DrawableHitObject hitObject)
        {
            if (hitObject.HitObject is IHasDuration e)
            {
                float length = LengthAtTime(hitObject.HitObject.StartTime, e.EndTime);
                if (scrollingAxis == 0)
                    hitObject.Width = length;
                else
                    hitObject.Height = length;
            }

            foreach (var obj in hitObject.NestedHitObjects)
            {
                updateLayoutRecursive(obj);

                // Nested hitobjects don't need to scroll, but they do need accurate positions
                updatePosition(obj, hitObject.HitObject.StartTime);
            }
        }

        private void updatePosition(DrawableHitObject hitObject, double currentTime)
        {
            float position = PositionAtTime(hitObject.HitObject.StartTime, currentTime);

            if (scrollingAxis == 0)
                hitObject.X = position;
            else
                hitObject.Y = position;
        }
    }
}