osu-lazer/osu.Game/Screens/Edit/Compose/Components/Timeline/ZoomableScrollContainer.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 osu.Framework.Allocation;
using osu.Framework.Graphics;
using osu.Framework.Graphics.Containers;
using osu.Framework.Graphics.Transforms;
using osu.Framework.Input.Events;
using osu.Framework.Layout;
using osu.Framework.Timing;
using osu.Framework.Utils;
using osu.Game.Graphics.Containers;
using osuTK;

namespace osu.Game.Screens.Edit.Compose.Components.Timeline
{
    public partial class ZoomableScrollContainer : OsuScrollContainer
    {
        /// <summary>
        /// The time to zoom into/out of a point.
        /// All user scroll input will be overwritten during the zoom transform.
        /// </summary>
        public double ZoomDuration;

        /// <summary>
        /// The easing with which to transform the zoom.
        /// </summary>
        public Easing ZoomEasing;

        private readonly Container zoomedContent;
        protected override Container<Drawable> Content => zoomedContent;

        /// <summary>
        /// The current zoom level of <see cref="ZoomableScrollContainer"/>.
        /// It may differ from <see cref="Zoom"/> during transitions.
        /// </summary>
        public float CurrentZoom { get; private set; } = 1;

        private bool isZoomSetUp;

        [Resolved]
        private IFrameBasedClock? editorClock { get; set; }

        private readonly LayoutValue zoomedContentWidthCache = new LayoutValue(Invalidation.DrawSize);

        private float minZoom;
        private float maxZoom;

        /// <summary>
        /// Creates a <see cref="ZoomableScrollContainer"/> with no zoom range.
        /// Functionality will be disabled until zoom is set up via <see cref="SetupZoom"/>.
        /// </summary>
        protected ZoomableScrollContainer()
            : base(Direction.Horizontal)
        {
            base.Content.Add(zoomedContent = new Container
            {
                RelativeSizeAxes = Axes.Y,
                // We must hide content until SetupZoom is called.
                // If not, a child component that relies on its DrawWidth (via RelativeSizeAxes) may see a very incorrect value
                // momentarily, as noticed in the TimelineTickDisplay, which would render thousands of ticks incorrectly.
                Alpha = 0,
            });

            AddLayout(zoomedContentWidthCache);
        }

        /// <summary>
        /// Creates a <see cref="ZoomableScrollContainer"/> with a defined zoom range.
        /// </summary>
        public ZoomableScrollContainer(float minimum, float maximum, float initial)
            : this()
        {
            SetupZoom(initial, minimum, maximum);
        }

        /// <summary>
        /// Sets up the minimum and maximum range of this zoomable scroll container, along with the initial zoom value.
        /// </summary>
        /// <param name="initial">The initial zoom value, applied immediately.</param>
        /// <param name="minimum">The minimum zoom value.</param>
        /// <param name="maximum">The maximum zoom value.</param>
        protected void SetupZoom(float initial, float minimum, float maximum)
        {
            if (minimum < 1)
                throw new ArgumentException($"{nameof(minimum)} ({minimum}) must be >= 1.", nameof(maximum));

            if (maximum < 1)
                throw new ArgumentException($"{nameof(maximum)} ({maximum}) must be >= 1.", nameof(maximum));

            if (minimum > maximum)
                throw new ArgumentException($"{nameof(minimum)} ({minimum}) must be less than {nameof(maximum)} ({maximum})");

            if (initial < minimum || initial > maximum)
                throw new ArgumentException($"{nameof(initial)} ({initial}) must be between {nameof(minimum)} ({minimum}) and {nameof(maximum)} ({maximum})");

            minZoom = minimum;
            maxZoom = maximum;

            CurrentZoom = zoomTarget = initial;
            zoomedContentWidthCache.Invalidate();

            isZoomSetUp = true;
            zoomedContent.Show();
        }

        /// <summary>
        /// Gets or sets the content zoom level of this <see cref="ZoomableScrollContainer"/>.
        /// </summary>
        public float Zoom
        {
            get => zoomTarget;
            set => updateZoom(value);
        }

        private void updateZoom(float value)
        {
            if (!isZoomSetUp)
                return;

            float newZoom = Math.Clamp(value, minZoom, maxZoom);

            if (IsLoaded)
                setZoomTarget(newZoom, ToSpaceOfOtherDrawable(new Vector2(DrawWidth / 2, 0), zoomedContent).X);
            else
                CurrentZoom = zoomTarget = newZoom;
        }

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

            if (!zoomedContentWidthCache.IsValid)
                updateZoomedContentWidth();
        }

        protected override bool OnScroll(ScrollEvent e)
        {
            if (e.AltPressed)
            {
                // zoom when holding alt.
                AdjustZoomRelatively(e.ScrollDelta.Y, zoomedContent.ToLocalSpace(e.ScreenSpaceMousePosition).X);
                return true;
            }

            // can't handle scroll correctly while playing.
            // the editor will handle this case for us.
            if (editorClock?.IsRunning == true)
                return false;

            return base.OnScroll(e);
        }

        private void updateZoomedContentWidth()
        {
            zoomedContent.Width = DrawWidth * CurrentZoom;
            zoomedContentWidthCache.Validate();
        }

        public void AdjustZoomRelatively(float change, float? focusPoint = null)
        {
            if (!isZoomSetUp)
                return;

            const float zoom_change_sensitivity = 0.02f;

            setZoomTarget(zoomTarget + change * (maxZoom - minZoom) * zoom_change_sensitivity, focusPoint);
        }

        private float zoomTarget = 1;

        private void setZoomTarget(float newZoom, float? focusPoint = null)
        {
            zoomTarget = Math.Clamp(newZoom, minZoom, maxZoom);
            focusPoint ??= zoomedContent.ToLocalSpace(ToScreenSpace(new Vector2(DrawWidth / 2, 0))).X;

            transformZoomTo(zoomTarget, focusPoint.Value, ZoomDuration, ZoomEasing);

            OnZoomChanged();
        }

        private void transformZoomTo(float newZoom, float focusPoint, double duration = 0, Easing easing = Easing.None)
            => this.TransformTo(this.PopulateTransform(new TransformZoom(focusPoint, zoomedContent.DrawWidth, Current), newZoom, duration, easing));

        /// <summary>
        /// Invoked when <see cref="Zoom"/> has changed.
        /// </summary>
        protected virtual void OnZoomChanged()
        {
        }

        private class TransformZoom : Transform<float, ZoomableScrollContainer>
        {
            /// <summary>
            /// The focus point in absolute coordinates local to the content.
            /// </summary>
            private readonly float focusPoint;

            /// <summary>
            /// The size of the content.
            /// </summary>
            private readonly float contentSize;

            /// <summary>
            /// The scroll offset at the start of the transform.
            /// </summary>
            private readonly float scrollOffset;

            /// <summary>
            /// Transforms <see cref="ZoomableScrollContainer.CurrentZoom"/> to a new value.
            /// </summary>
            /// <param name="focusPoint">The focus point in absolute coordinates local to the content.</param>
            /// <param name="contentSize">The size of the content.</param>
            /// <param name="scrollOffset">The scroll offset at the start of the transform.</param>
            public TransformZoom(float focusPoint, float contentSize, float scrollOffset)
            {
                this.focusPoint = focusPoint;
                this.contentSize = contentSize;
                this.scrollOffset = scrollOffset;
            }

            public override string TargetMember => nameof(CurrentZoom);

            private float valueAt(double time)
            {
                if (time < StartTime) return StartValue;
                if (time >= EndTime) return EndValue;

                return Interpolation.ValueAt(time, StartValue, EndValue, StartTime, EndTime, Easing);
            }

            protected override void Apply(ZoomableScrollContainer d, double time)
            {
                float newZoom = valueAt(time);

                float focusOffset = focusPoint - scrollOffset;
                float expectedWidth = d.DrawWidth * newZoom;
                float targetOffset = expectedWidth * (focusPoint / contentSize) - focusOffset;

                d.CurrentZoom = newZoom;
                d.updateZoomedContentWidth();

                // Temporarily here to make sure ScrollTo gets the correct DrawSize for scrollable area.
                // TODO: Make sure draw size gets invalidated properly on the framework side, and remove this once it is.
                d.Invalidate(Invalidation.DrawSize);
                d.ScrollTo(targetOffset, false);
            }

            protected override void ReadIntoStartValue(ZoomableScrollContainer d) => StartValue = d.CurrentZoom;
        }
    }
}