Add failing test

osu.Game.Tests/NonVisual/BarLineGeneratorTest.cs

@@ -0,0 +1,73 @@
+// 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 NUnit.Framework;
+using osu.Framework.Utils;
+using osu.Game.Beatmaps;
+using osu.Game.Beatmaps.ControlPoints;
+using osu.Game.Beatmaps.Timing;
+using osu.Game.Rulesets.Objects;
+
+namespace osu.Game.Tests.NonVisual
+{
+    public class BarLineGeneratorTest
+    {
+        [Test]
+        public void TestRoundingErrorCompensation()
+        {
+            // The aim of this test is to make sure bar line generation compensates for floating-point errors.
+            // The premise of the test is that we have a single timing point that should result in bar lines
+            // that start at a time point that is a whole number every seventh beat.
+
+            // The fact it's every seventh beat is important - it's a number indivisible by 2, which makes
+            // it susceptible to rounding inaccuracies. In fact this was originally spotted in cases of maps
+            // that met exactly this criteria.
+
+            const int beat_length_numerator = 2000;
+            const int beat_length_denominator = 7;
+            const TimeSignatures signature = TimeSignatures.SimpleQuadruple;
+
+            var beatmap = new Beatmap
+            {
+                HitObjects = new List<HitObject>
+                {
+                    new HitObject { StartTime = 0 },
+                    new HitObject { StartTime = 120_000 }
+                },
+                ControlPointInfo = new ControlPointInfo()
+            };
+
+            beatmap.ControlPointInfo.Add(0, new TimingControlPoint
+            {
+                BeatLength = (double)beat_length_numerator / beat_length_denominator,
+                TimeSignature = signature
+            });
+
+            var barLines = new BarLineGenerator<BarLine>(beatmap).BarLines;
+
+            for (int i = 0; i * beat_length_denominator < barLines.Count; i++)
+            {
+                var barLine = barLines[i * beat_length_denominator];
+                var expectedTime = beat_length_numerator * (int)signature * i;
+
+                // every seventh bar's start time should be at least greater than the whole number we expect.
+                // It cannot be less, as that can affect overlapping scroll algorithms
+                // (the previous timing point might be chosen incorrectly if this is not the case)
+                Assert.GreaterOrEqual(barLine.StartTime, expectedTime);
+
+                // on the other side, make sure we don't stray too far from the expected time either.
+                Assert.IsTrue(Precision.AlmostEquals(barLine.StartTime, expectedTime));
+
+                // check major/minor lines for good measure too
+                Assert.AreEqual(i % (int)signature == 0, barLine.Major);
+            }
+        }
+
+        private class BarLine : IBarLine
+        {
+            public double StartTime { get; set; }
+            public bool Major { get; set; }
+        }
+    }
+}