Add circular grid

osu.Game.Rulesets.Osu/Edit/OsuGridToolboxGroup.cs

@@ -100,7 +100,10 @@ private void load()
                             () => new SpriteIcon { Icon = FontAwesome.Regular.Square }),
                         new RadioButton("Triangle",
                             () => GridType.Value = PositionSnapGridType.Triangle,
-                            () => new Triangle())
+                            () => new Triangle()),
+                        new RadioButton("Circle",
+                            () => GridType.Value = PositionSnapGridType.Circle,
+                            () => new SpriteIcon { Icon = FontAwesome.Regular.Circle }),
                     }
                 },
             };
@@ -177,5 +180,6 @@ public enum PositionSnapGridType
     {
         Square,
         Triangle,
+        Circle,
     }
 }

osu.Game.Rulesets.Osu/Edit/OsuHitObjectComposer.cs

@@ -135,6 +135,14 @@ private void updatePositionSnapGrid(ValueChangedEvent<PositionSnapGridType> obj)
                     positionSnapGrid = triangularPositionSnapGrid;
                     break;
 
+                case PositionSnapGridType.Circle:
+                    var circularPositionSnapGrid = new CircularPositionSnapGrid();
+
+                    OsuGridToolboxGroup.Spacing.BindValueChanged(s => circularPositionSnapGrid.Spacing = s.NewValue, true);
+
+                    positionSnapGrid = circularPositionSnapGrid;
+                    break;
+
                 default:
                     throw new NotImplementedException($"{OsuGridToolboxGroup.GridType} has an incorrect value.");
             }

osu.Game/Screens/Edit/Compose/Components/CircularPositionSnapGrid.cs

@@ -0,0 +1,106 @@
+// 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;
+using System.Collections.Generic;
+using System.Linq;
+using osu.Framework.Graphics;
+using osu.Framework.Graphics.Containers;
+using osu.Framework.Graphics.Shapes;
+using osu.Framework.Utils;
+using osu.Game.Utils;
+using osuTK;
+
+namespace osu.Game.Screens.Edit.Compose.Components
+{
+    public partial class CircularPositionSnapGrid : PositionSnapGrid
+    {
+        private float spacing = 1;
+
+        /// <summary>
+        /// The spacing between grid lines of this <see cref="CircularPositionSnapGrid"/>.
+        /// </summary>
+        public float Spacing
+        {
+            get => spacing;
+            set
+            {
+                if (spacing <= 0)
+                    throw new ArgumentException("Grid spacing must be positive.");
+
+                spacing = value;
+                GridCache.Invalidate();
+            }
+        }
+
+        protected override void CreateContent()
+        {
+            var drawSize = DrawSize;
+
+            // Calculate the maximum distance from the origin to the edge of the grid.
+            float maxDist = MathF.Max(
+                MathF.Max(StartPosition.Length, (StartPosition - drawSize).Length),
+                MathF.Max((StartPosition - new Vector2(drawSize.X, 0)).Length, (StartPosition - new Vector2(0, drawSize.Y)).Length)
+            );
+
+            generateCircles((int)(maxDist / Spacing) + 1);
+
+            GenerateOutline(drawSize);
+        }
+
+        private void generateCircles(int count)
+        {
+            // Make lines the same width independent of display resolution.
+            float lineWidth = 2 * DrawWidth / ScreenSpaceDrawQuad.Width;
+
+            List<CircularContainer> generatedCircles = new List<CircularContainer>();
+
+            for (int i = 0; i < count; i++)
+            {
+                // Add a minimum diameter so the center circle is clearly visible.
+                float diameter = MathF.Max(lineWidth * 1.5f, i * Spacing * 2);
+
+                var gridCircle = new CircularContainer
+                {
+                    BorderColour = Colour4.White,
+                    BorderThickness = lineWidth,
+                    Alpha = 0.2f,
+                    Origin = Anchor.Centre,
+                    RelativeSizeAxes = Axes.None,
+                    Width = diameter,
+                    Height = diameter,
+                    Position = StartPosition,
+                    Masking = true,
+                    Child = new Box
+                    {
+                        RelativeSizeAxes = Axes.Both,
+                        AlwaysPresent = true,
+                        Alpha = 0f,
+                    }
+                };
+
+                generatedCircles.Add(gridCircle);
+            }
+
+            if (generatedCircles.Count == 0)
+                return;
+
+            generatedCircles.First().Alpha = 0.8f;
+
+            AddRangeInternal(generatedCircles);
+        }
+
+        public override Vector2 GetSnappedPosition(Vector2 original)
+        {
+            Vector2 relativeToStart = original - StartPosition;
+
+            if (relativeToStart.LengthSquared < Precision.FLOAT_EPSILON)
+                return StartPosition;
+
+            float length = relativeToStart.Length;
+            float wantedLength = MathF.Round(length / Spacing) * Spacing;
+
+            return StartPosition + Vector2.Multiply(relativeToStart, wantedLength / length);
+        }
+    }
+}