Refactored Arrange to operate by rows

Author: Avid29

components/StretchPanel/src/StretchPanel.Structs.cs

@@ -0,0 +1,155 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+namespace CommunityToolkit.WinUI.Controls;
+
+public partial class StretchPanel
+{
+    /// <summary>
+    /// A struct representing the specifications of a row or column in the panel.
+    /// </summary>
+    private struct RowSpec
+    {
+        public RowSpec(GridLength layout, UVCoord desiredSize)
+        {
+            switch (layout.GridUnitType)
+            {
+                case GridUnitType.Auto:
+                    ReservedSpace = desiredSize.U;
+                    break;
+                case GridUnitType.Pixel:
+                    ReservedSpace = layout.Value;
+                    break;
+                case GridUnitType.Star:
+                    PortionsSum = layout.Value;
+                    MinPortionSize = desiredSize.U / layout.Value;
+                    break;
+            }
+
+            MaxOffAxisSize = desiredSize.V;
+            ItemsCount = 1;
+        }
+
+        /// <summary>
+        /// Gets the total reserved space for spacing in the row/column.
+        /// </summary>
+        /// <remarks>
+        /// Items with a fixed size or auto size contribute to this value.
+        /// </remarks>
+        public double ReservedSpace { get; private set; }
+
+        /// <summary>
+        /// Gets the sum of portions in the row/column.
+        /// </summary>
+        /// <remarks>
+        /// Items with a star-sized length contribute to this value.
+        /// </remarks>
+        public double PortionsSum { get; private set; }
+
+        /// <summary>
+        /// Gets the maximum width/height of items in the row/column.
+        /// </summary>
+        /// <remarks>
+        /// Width in vertical orientation, height in horizontal orientation.
+        /// </remarks>
+        public double MaxOffAxisSize { get; private set; }
+
+        /// <summary>
+        /// Gets the minimum size of a portion in the row/column.
+        /// </summary>
+        public double MinPortionSize { get; private set; }
+
+        /// <summary>
+        /// Gets the number of items in the row/column.
+        /// </summary>
+        public int ItemsCount { get; private set; }
+
+        public bool TryAdd(RowSpec addend, double spacing, double maxSize)
+        {
+            // Check if adding the new spec would exceed the maximum size
+            var sum = this + addend;
+            if (sum.Measure(spacing) > maxSize)
+                return false;
+
+            // Update the current spec to include the new spec
+            this = sum;
+            return true;
+        }
+
+        public readonly double Measure(double spacing)
+        {
+            var totalSpacing = (ItemsCount - 1) * spacing;
+            var totalSize = ReservedSpace + totalSpacing;
+
+            // Add star-sized items if applicable
+            if (!double.IsNaN(MinPortionSize) && !double.IsInfinity(MinPortionSize))
+                totalSize += MinPortionSize * PortionsSum;
+
+            return totalSize;
+        }
+
+        public static RowSpec operator +(RowSpec a, RowSpec b)
+        {
+            var combined = new RowSpec
+            {
+                ReservedSpace = a.ReservedSpace + b.ReservedSpace,
+                PortionsSum = a.PortionsSum + b.PortionsSum,
+                MinPortionSize = Math.Max(a.MinPortionSize, b.MinPortionSize),
+                MaxOffAxisSize = Math.Max(a.MaxOffAxisSize, b.MaxOffAxisSize),
+                ItemsCount = a.ItemsCount + b.ItemsCount
+            };
+            return combined;
+        }
+    }
+
+    /// <summary>
+    /// A struct for mapping X/Y coordinates to an orientation adjusted U/V coordinate system.
+    /// </summary>
+    private struct UVCoord(double x, double y, Orientation orientation)
+    {
+        private readonly bool _horizontal = orientation is Orientation.Horizontal;
+
+        public UVCoord(Size size, Orientation orientation) : this(size.Width, size.Height, orientation)
+        {
+        }
+
+        public double X { get; set; } = x;
+
+        public double Y { get; set; } = y;
+
+        public double U
+        {
+            readonly get => _horizontal ? X : Y;
+            set
+            {
+                if (_horizontal)
+                {
+                    X = value;
+                }
+                else
+                {
+                    Y = value;
+                }
+            }
+        }
+
+        public double V
+        {
+            readonly get => _horizontal ? Y : X;
+            set
+            {
+                if (_horizontal)
+                {
+                    Y = value;
+                }
+                else
+                {
+                    X = value;
+                }
+            }
+        }
+
+        public readonly Size Size => new(X, Y);
+    }
+}