Rename *ScrollingDrawableTimingSection -> *ScrollingContainer, move LinearScrollingContainer to osu.Game, make SpeedAdjustmentContainer non-abstract.

osu.Game.Rulesets.Mania/Timing/GravityScrollingContainer.cs

@@ -0,0 +1,61 @@
+// Copyright (c) 2007-2017 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using osu.Framework.Graphics;
+using osu.Game.Rulesets.Timing;
+
+namespace osu.Game.Rulesets.Mania.Timing
+{
+    /// <summary>
+    /// A <see cref="ScrollingContainer"/> that emulates a form of gravity where hit objects speed up over time.
+    /// </summary>
+    internal class GravityScrollingContainer : ScrollingContainer
+    {
+        private readonly MultiplierControlPoint controlPoint;
+
+        public GravityScrollingContainer(MultiplierControlPoint controlPoint)
+        {
+            this.controlPoint = controlPoint;
+        }
+
+        protected override void UpdateAfterChildren()
+        {
+            base.UpdateAfterChildren();
+
+            // The gravity-adjusted start position
+            float startPos = (float)computeGravityTime(controlPoint.StartTime);
+            // The gravity-adjusted end position
+            float endPos = (float)computeGravityTime(controlPoint.StartTime + RelativeChildSize.Y);
+
+            Y = startPos;
+            Height = endPos - startPos;
+        }
+
+        /// <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 VisibleTimeRange - acceleration * relativeTime * relativeTime * sign;
+        }
+
+        /// <summary>
+        /// The acceleration due to "gravity" of the content of this container.
+        /// </summary>
+        private double acceleration => 1 / VisibleTimeRange;
+
+        /// <summary>
+        /// Computes the current time relative to <paramref name="time"/>, accounting for <see cref="ScrollingContainer.VisibleTimeRange"/>.
+        /// </summary>
+        /// <param name="time">The non-offset time.</param>
+        /// <returns>The current time relative to <paramref name="time"/> - <see cref="ScrollingContainer.VisibleTimeRange"/>. </returns>
+        private double relativeTimeAt(double time) => Time.Current - time + VisibleTimeRange;
+    }
+}