Add hitobject lifetime model

osu.Game/Rulesets/Objects/HitObjectLifetimeEntry.cs

@@ -0,0 +1,98 @@
+// 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 osu.Framework.Graphics.Performance;
+using osu.Game.Rulesets.Objects.Drawables;
+
+namespace osu.Game.Rulesets.Objects
+{
+    /// <summary>
+    /// A <see cref="LifetimeEntry"/> that stores the lifetime for a <see cref="HitObject"/>.
+    /// </summary>
+    public class HitObjectLifetimeEntry : LifetimeEntry
+    {
+        /// <summary>
+        /// The <see cref="HitObject"/>.
+        /// </summary>
+        public readonly HitObject HitObject;
+
+        /// <summary>
+        /// Creates a new <see cref="HitObjectLifetimeEntry"/>.
+        /// </summary>
+        /// <param name="hitObject">The <see cref="HitObject"/> to store the lifetime of.</param>
+        public HitObjectLifetimeEntry(HitObject hitObject)
+        {
+            HitObject = hitObject;
+            ResetLifetimeStart();
+        }
+
+        // The lifetime start, as set by the hitobject.
+        private double realLifetimeStart = double.MinValue;
+
+        /// <summary>
+        /// The time at which the <see cref="HitObject"/> should become alive.
+        /// </summary>
+        public new double LifetimeStart
+        {
+            get => realLifetimeStart;
+            set => setLifetime(realLifetimeStart = value, LifetimeEnd);
+        }
+
+        // The lifetime end, as set by the hitobject.
+        private double realLifetimeEnd = double.MaxValue;
+
+        /// <summary>
+        /// The time at which the <see cref="HitObject"/> should become dead.
+        /// </summary>
+        public new double LifetimeEnd
+        {
+            get => realLifetimeEnd;
+            set => setLifetime(LifetimeStart, realLifetimeEnd = value);
+        }
+
+        private void setLifetime(double start, double end)
+        {
+            if (keepAlive)
+            {
+                start = double.MinValue;
+                end = double.MaxValue;
+            }
+
+            base.LifetimeStart = start;
+            base.LifetimeEnd = end;
+        }
+
+        private bool keepAlive;
+
+        /// <summary>
+        /// Whether the <see cref="HitObject"/> should be kept always alive.
+        /// </summary>
+        internal bool KeepAlive
+        {
+            set
+            {
+                if (keepAlive == value)
+                    return;
+
+                keepAlive = value;
+                setLifetime(realLifetimeStart, realLifetimeEnd);
+            }
+        }
+
+        /// <summary>
+        /// A safe offset prior to the start time of <see cref="HitObject"/> at which it may begin displaying contents.
+        /// By default, <see cref="HitObject"/>s are assumed to display their contents within 10 seconds prior to their start time.
+        /// </summary>
+        /// <remarks>
+        /// This is only used as an optimisation to delay the initial update of the <see cref="HitObject"/> and may be tuned more aggressively if required.
+        /// It is indirectly used to decide the automatic transform offset provided to <see cref="DrawableHitObject.UpdateInitialTransforms"/>.
+        /// A more accurate <see cref="LifetimeStart"/> should be set for further optimisation (in <see cref="DrawableHitObject.LoadComplete"/>, for example).
+        /// </remarks>
+        protected virtual double InitialLifetimeOffset => 10000;
+
+        /// <summary>
+        /// Resets <see cref="LifetimeStart"/> according to the start time of the <see cref="HitObject"/>.
+        /// </summary>
+        internal void ResetLifetimeStart() => LifetimeStart = HitObject.StartTime - InitialLifetimeOffset;
+    }
+}