Add rectangular position snap grid

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

@@ -0,0 +1,101 @@
+// 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 osu.Framework.Graphics;
+using osu.Framework.Graphics.Containers;
+using osu.Framework.Graphics.Shapes;
+using osu.Framework.Layout;
+using osuTK;
+
+namespace osu.Game.Screens.Edit.Compose.Components
+{
+    public class RectangularPositionSnapGrid : CompositeDrawable
+    {
+        /// <summary>
+        /// The position of the origin of this <see cref="RectangularPositionSnapGrid"/> in local coordinates.
+        /// </summary>
+        public Vector2 StartPosition { get; }
+
+        /// <summary>
+        /// The spacing between grid lines of this <see cref="RectangularPositionSnapGrid"/>.
+        /// </summary>
+        public Vector2 Spacing { get; }
+
+        private readonly LayoutValue gridCache = new LayoutValue(Invalidation.RequiredParentSizeToFit);
+
+        public RectangularPositionSnapGrid(Vector2 startPosition, Vector2 spacing)
+        {
+            StartPosition = startPosition;
+            Spacing = spacing;
+
+            AddLayout(gridCache);
+        }
+
+        protected override void Update()
+        {
+            base.Update();
+
+            if (!gridCache.IsValid)
+            {
+                ClearInternal();
+                createContent();
+                gridCache.Validate();
+            }
+        }
+
+        private void createContent()
+        {
+            var drawSize = DrawSize;
+
+            generateGridLines(Direction.Horizontal, StartPosition.Y, 0, -Spacing.Y);
+            generateGridLines(Direction.Horizontal, StartPosition.Y, drawSize.Y, Spacing.Y);
+
+            generateGridLines(Direction.Vertical, StartPosition.X, 0, -Spacing.X);
+            generateGridLines(Direction.Vertical, StartPosition.X, drawSize.X, Spacing.X);
+        }
+
+        private void generateGridLines(Direction direction, float startPosition, float endPosition, float step)
+        {
+            int index = 0;
+            float currentPosition = startPosition;
+
+            while ((endPosition - currentPosition) * Math.Sign(step) > 0)
+            {
+                var gridLine = new Box
+                {
+                    Colour = Colour4.White,
+                    Alpha = index == 0 ? 0.3f : 0.1f,
+                    EdgeSmoothness = new Vector2(0.2f)
+                };
+
+                if (direction == Direction.Horizontal)
+                {
+                    gridLine.RelativeSizeAxes = Axes.X;
+                    gridLine.Height = 1;
+                    gridLine.Y = currentPosition;
+                }
+                else
+                {
+                    gridLine.RelativeSizeAxes = Axes.Y;
+                    gridLine.Width = 1;
+                    gridLine.X = currentPosition;
+                }
+
+                AddInternal(gridLine);
+
+                index += 1;
+                currentPosition = startPosition + index * step;
+            }
+        }
+
+        public Vector2 GetSnappedPosition(Vector2 original)
+        {
+            Vector2 relativeToStart = original - StartPosition;
+            Vector2 offset = Vector2.Divide(relativeToStart, Spacing);
+            Vector2 roundedOffset = new Vector2(MathF.Round(offset.X), MathF.Round(offset.Y));
+
+            return StartPosition + Vector2.Multiply(roundedOffset, Spacing);
+        }
+    }
+}