Add very basic distance snap grid for catch editor

osu.Game.Rulesets.Catch/Edit/CatchDistanceSnapGrid.cs

@@ -0,0 +1,107 @@
+// 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 System.Linq;
+using JetBrains.Annotations;
+using osu.Framework.Allocation;
+using osu.Framework.Graphics;
+using osu.Framework.Graphics.Containers;
+using osu.Framework.Graphics.Lines;
+using osu.Framework.Graphics.Primitives;
+using osu.Game.Rulesets.Edit;
+using osu.Game.Rulesets.UI;
+using osu.Game.Rulesets.UI.Scrolling;
+using osuTK;
+
+namespace osu.Game.Rulesets.Catch.Edit
+{
+    public class CatchDistanceSnapGrid : CompositeDrawable
+    {
+        public double StartTime { get; set; }
+
+        public float StartX { get; set; }
+
+        private readonly double[] velocities;
+
+        private readonly List<Path> verticalPaths = new List<Path>();
+
+        private readonly List<List<Vector2>> verticalLineVertices = new List<List<Vector2>>();
+
+        [Resolved]
+        private Playfield playfield { get; set; }
+
+        private ScrollingHitObjectContainer hitObjectContainer => (ScrollingHitObjectContainer)playfield.HitObjectContainer;
+
+        public CatchDistanceSnapGrid(double[] velocities)
+        {
+            RelativeSizeAxes = Axes.Both;
+            Anchor = Anchor.BottomLeft;
+
+            this.velocities = velocities;
+
+            for (int i = 0; i < velocities.Length; i++)
+            {
+                verticalPaths.Add(new SmoothPath
+                {
+                    PathRadius = 2,
+                    Alpha = 0.5f,
+                });
+
+                verticalLineVertices.Add(new List<Vector2> { Vector2.Zero, Vector2.Zero });
+            }
+
+            AddRangeInternal(verticalPaths);
+        }
+
+        protected override void Update()
+        {
+            base.Update();
+
+            float startY = hitObjectContainer.PositionAtTime(StartTime);
+
+            for (int i = 0; i < velocities.Length; i++)
+            {
+                double velocity = velocities[i];
+
+                // The line ends at the top of the screen.
+                double endTime = hitObjectContainer.TimeAtPosition(-hitObjectContainer.DrawHeight, hitObjectContainer.Time.Current);
+
+                float x = (float)((endTime - StartTime) * velocity);
+                float y = hitObjectContainer.PositionAtTime(endTime, StartTime);
+
+                List<Vector2> lineVertices = verticalLineVertices[i];
+                lineVertices[0] = new Vector2(StartX, startY);
+                lineVertices[1] = lineVertices[0] + new Vector2(x, y);
+
+                var verticalPath = verticalPaths[i];
+                verticalPath.Vertices = verticalLineVertices[i];
+                verticalPath.OriginPosition = verticalPath.PositionInBoundingBox(Vector2.Zero);
+            }
+        }
+
+        [CanBeNull]
+        public SnapResult GetSnappedPosition(Vector2 screenSpacePosition)
+        {
+            double time = hitObjectContainer.TimeAtScreenSpacePosition(screenSpacePosition);
+
+            return enumerateSnappingCandidates(time)
+                   .OrderBy(pos => Vector2.DistanceSquared(screenSpacePosition, pos.ScreenSpacePosition))
+                   .FirstOrDefault();
+        }
+
+        private IEnumerable<SnapResult> enumerateSnappingCandidates(double time)
+        {
+            float y = hitObjectContainer.PositionAtTime(time);
+
+            foreach (double velocity in velocities)
+            {
+                float x = (float)(StartX + (time - StartTime) * velocity);
+                Vector2 screenSpacePosition = hitObjectContainer.ToScreenSpace(new Vector2(x, y + hitObjectContainer.DrawHeight));
+                yield return new SnapResult(screenSpacePosition, time);
+            }
+        }
+
+        protected override bool ComputeIsMaskedAway(RectangleF maskingBounds) => false;
+    }
+}