Merge pull request #4673 from peppy/frame-stability-initial-seek

Amend FrameStabilityContainer's initial seek behaviour

osu.Game.Tests/Visual/Gameplay/TestCaseFrameStabilityContainer.cs

@@ -0,0 +1,150 @@
+// 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 NUnit.Framework;
+using osu.Framework.Graphics;
+using osu.Framework.Graphics.Containers;
+using osu.Framework.Timing;
+using osu.Game.Graphics.Sprites;
+using osu.Game.Rulesets.UI;
+
+namespace osu.Game.Tests.Visual.Gameplay
+{
+    public class TestCaseFrameStabilityContainer : OsuTestCase
+    {
+        private readonly ManualClock manualClock;
+
+        private readonly Container mainContainer;
+
+        private ClockConsumingChild consumer;
+
+        public TestCaseFrameStabilityContainer()
+        {
+            Child = mainContainer = new Container
+            {
+                RelativeSizeAxes = Axes.Both,
+                Clock = new FramedClock(manualClock = new ManualClock()),
+            };
+        }
+
+        [Test]
+        public void TestLargeJumps()
+        {
+            seekManualTo(0);
+            createStabilityContainer();
+            seekManualTo(100000);
+
+            confirmSeek(100000);
+            checkFrameCount(6000);
+
+            seekManualTo(0);
+
+            confirmSeek(0);
+            checkFrameCount(12000);
+        }
+
+        [Test]
+        public void TestSmallJumps()
+        {
+            seekManualTo(0);
+            createStabilityContainer();
+            seekManualTo(40);
+
+            confirmSeek(40);
+            checkFrameCount(3);
+
+            seekManualTo(0);
+
+            confirmSeek(0);
+            checkFrameCount(6);
+        }
+
+        [Test]
+        public void TestSingleFrameJump()
+        {
+            seekManualTo(0);
+            createStabilityContainer();
+            seekManualTo(8);
+            confirmSeek(8);
+            checkFrameCount(1);
+
+            seekManualTo(16);
+            confirmSeek(16);
+            checkFrameCount(2);
+        }
+
+        [Test]
+        public void TestInitialSeek()
+        {
+            seekManualTo(100000);
+            createStabilityContainer();
+
+            confirmSeek(100000);
+            checkFrameCount(0);
+        }
+
+        private void createStabilityContainer() => AddStep("create container", () => mainContainer.Child = new FrameStabilityContainer().WithChild(consumer = new ClockConsumingChild()));
+
+        private void seekManualTo(double time) => AddStep($"seek manual clock to {time}", () => manualClock.CurrentTime = time);
+
+        private void confirmSeek(double time) => AddUntilStep($"wait for seek to {time}", () => consumer.Clock.CurrentTime == time);
+
+        private void checkFrameCount(int frames) =>
+            AddAssert($"elapsed frames is {frames}", () => consumer.ElapsedFrames == frames);
+
+        public class ClockConsumingChild : CompositeDrawable
+        {
+            private readonly OsuSpriteText text;
+            private readonly OsuSpriteText text2;
+            private readonly OsuSpriteText text3;
+
+            public ClockConsumingChild()
+            {
+                Anchor = Anchor.Centre;
+                Origin = Anchor.Centre;
+
+                InternalChildren = new Drawable[]
+                {
+                    new FillFlowContainer
+                    {
+                        RelativeSizeAxes = Axes.Both,
+                        Direction = FillDirection.Vertical,
+                        Children = new Drawable[]
+                        {
+                            text = new OsuSpriteText
+                            {
+                                Anchor = Anchor.Centre,
+                                Origin = Anchor.Centre,
+                            },
+                            text2 = new OsuSpriteText
+                            {
+                                Anchor = Anchor.Centre,
+                                Origin = Anchor.Centre,
+                            },
+                            text3 = new OsuSpriteText
+                            {
+                                Anchor = Anchor.Centre,
+                                Origin = Anchor.Centre,
+                            },
+                        }
+                    },
+                };
+            }
+
+            public int ElapsedFrames;
+
+            protected override void Update()
+            {
+                base.Update();
+
+                if (Clock.ElapsedFrameTime != 0)
+                    ElapsedFrames++;
+
+                text.Text = $"current time: {Clock.CurrentTime:F0}";
+                if (Clock.ElapsedFrameTime != 0)
+                    text2.Text = $"last elapsed frame time: {Clock.ElapsedFrameTime:F0}";
+                text3.Text = $"total frames: {ElapsedFrames:F0}";
+            }
+        }
+    }
+}

osu.Game/Rulesets/UI/FrameStabilityContainer.cs

@@ -68,6 +68,8 @@ protected override void LoadComplete()
 
         private const double sixty_frame_time = 1000.0 / 60;
 
+        private bool firstConsumption = true;
+
         public override bool UpdateSubTree()
         {
             requireMoreUpdateLoops = true;
@@ -103,7 +105,18 @@ private void updateClock()
 
             try
             {
-                if (Math.Abs(manualClock.CurrentTime - newProposedTime) > sixty_frame_time * 1.2f)
+                if (firstConsumption)
+                {
+                    // On the first update, frame-stability seeking would result in unexpected/unwanted behaviour.
+                    // Instead we perform an initial seek to the proposed time.
+                    manualClock.CurrentTime = newProposedTime;
+
+                    // do a second process to clear out ElapsedTime
+                    framedClock.ProcessFrame();
+
+                    firstConsumption = false;
+                }
+                else if (Math.Abs(manualClock.CurrentTime - newProposedTime) > sixty_frame_time * 1.2f)
                 {
                     newProposedTime = newProposedTime > manualClock.CurrentTime
                         ? Math.Min(newProposedTime, manualClock.CurrentTime + sixty_frame_time)