Add gravity timing change.

osu.Game.Rulesets.Mania/Timing/Drawables/DrawableGravityTimingChange.cs

@@ -8,11 +8,11 @@ namespace osu.Game.Rulesets.Mania.Timing.Drawables
 {
     public class DrawableGravityTimingChange : DrawableTimingChange
     {
-        private const double acceleration = 9.8f;
+        // Amount of time to travel this container such that
-        private const double terminal_velocity = 50f;
+        // at time = 0, gravityTime = timeSpan and
-
+        // at time = travel_time, gravityTime = 0
-        private const double duration = 2000;
+        // Where gravityTime is used as the position of the content
-
+        private const double travel_time = 1000;
 
         public DrawableGravityTimingChange(TimingChange timingChange)
             : base(timingChange)
@@ -23,17 +23,52 @@ namespace osu.Game.Rulesets.Mania.Timing.Drawables
         {
             base.Update();
 
-            var parent = (TimingChangeContainer)Parent;
+            // The gravity-adjusted start position
+            float startY = (float)computeGravityTime(TimingChange.Time);
+            // The gravity-adjusted end position
+            float endY = (float)computeGravityTime(TimingChange.Time + Content.RelativeCoordinateSpace.Y);
 
-            double elapsed = Math.Max(0, Time.Current - TimingChange.Time);
+            Content.Y = startY;
-
+            Content.Height = endY - startY;
-            // @ Current == TimingChange.Time - duration -> Y = TimingChange.Time
-            // @ Current == TimingChange.Time -> Y = 0
-            // @ Current == TimingChange.Time + x -> Y = -f(x)
-
-            double acceleration = elapsed / 2 / 1000 / 1000;
-
-            Content.Y = (float)(TimingChange.Time - 1 / 2f * acceleration * elapsed * elapsed);
         }
+
+        /// <summary>
+        /// Applies gravity to a time value based on the current time.
+        /// </summary>
+        /// <param name="time">The time value gravity should be applied to.</param>
+        /// <returns>The time after gravity is applied to <paramref name="time"/>.</returns>
+        private double computeGravityTime(double time)
+        {
+            double relativeTime = relativeTimeAt(time);
+
+            // The sign of the relative time, this is used to apply backwards acceleration leading into startTime
+            double sign = relativeTime < 0 ? -1 : 1;
+
+            return timeSpan - acceleration / 2 * relativeTime * relativeTime * sign;
+        }
+
+        /// <summary>
+        /// The time spanned by this container.
+        /// </summary>
+        private double timeSpan => RelativeCoordinateSpace.Y;
+
+        /// <summary>
+        /// The acceleration due to "gravity" of the content of this container.
+        /// </summary>
+        private double acceleration => 2 * timeSpan / travel_time / travel_time;
+
+        /// <summary>
+        /// Computes the current time relative to <paramref name="time"/>, accounting for <see cref="travel_time"/>.
+        /// </summary>
+        /// <param name="time">The non-offset time.</param>
+        /// <returns>The current time relative to <paramref name="time"/> - <see cref="travel_time"/>. </returns>
+        private double relativeTimeAt(double time) => Time.Current - time + travel_time;
+
+        /// <summary>
+        /// The velocity of the content of this container at a time.
+        /// </summary>
+        /// <param name="time">The non-offset time.</param>
+        /// <returns>The velocity at <paramref name="time"/>.</returns>
+        private double velocityAt(double time) => acceleration * relativeTimeAt(time);
     }
 }

osu.Game.Rulesets.Mania/Timing/Drawables/DrawableTimingChange.cs

@@ -10,7 +10,7 @@ namespace osu.Game.Rulesets.Mania.Timing.Drawables
 {
     public abstract class DrawableTimingChange : Container<DrawableHitObject>
     {
-        protected readonly TimingChange TimingChange;
+        public readonly TimingChange TimingChange;
 
         protected override Container<DrawableHitObject> Content => content;
         private readonly Container<DrawableHitObject> content;