feat(ui): port retained widget foundations

src/AcDream.App/UI/UiLayoutPolicy.cs

@@ -0,0 +1,151 @@
+namespace AcDream.App.UI;
+
+/// <summary>An inclusive integer pixel box, matching retail <c>Box2D</c>.</summary>
+public readonly record struct UiPixelRect(int X0, int Y0, int X1, int Y1)
+{
+    public int Width => X1 - X0 + 1;
+    public int Height => Y1 - Y0 + 1;
+
+    public static UiPixelRect FromPositionAndSize(int x, int y, int width, int height)
+        => new(x, y, x + width - 1, y + height - 1);
+}
+
+/// <summary>
+/// Exact retail raw-edge layout policy from
+/// <c>UIElement::UpdateForParentSizeChange @ 0x00462640</c>. Imported DAT elements
+/// retain all four independent modes; programmatic widgets continue to use
+/// <see cref="AnchorEdges"/>.
+/// </summary>
+public sealed class UiLayoutPolicy
+{
+    public uint LeftMode { get; }
+    public uint TopMode { get; }
+    public uint RightMode { get; }
+    public uint BottomMode { get; }
+    public UiPixelRect OriginalChild { get; private set; }
+    public UiPixelRect OriginalParent { get; private set; }
+    public bool PreserveCurrentWhenEmpty { get; set; }
+
+    public UiLayoutPolicy(
+        uint leftMode,
+        uint topMode,
+        uint rightMode,
+        uint bottomMode,
+        UiPixelRect originalChild,
+        UiPixelRect originalParent)
+    {
+        ValidateMode(leftMode, nameof(leftMode));
+        ValidateMode(topMode, nameof(topMode));
+        ValidateMode(rightMode, nameof(rightMode));
+        ValidateMode(bottomMode, nameof(bottomMode));
+        LeftMode = leftMode;
+        TopMode = topMode;
+        RightMode = rightMode;
+        BottomMode = bottomMode;
+        OriginalChild = originalChild;
+        OriginalParent = originalParent;
+    }
+
+    /// <summary>
+    /// Makes a controller-supplied geometry change the new design baseline while
+    /// retaining the raw retail edge modes.
+    /// </summary>
+    public void Rebase(UiPixelRect child, UiPixelRect parent)
+    {
+        OriginalChild = child;
+        OriginalParent = parent;
+    }
+
+    public UiPixelRect Apply(UiPixelRect currentChild, UiPixelRect currentParent)
+        => Apply(
+            LeftMode,
+            TopMode,
+            RightMode,
+            BottomMode,
+            OriginalChild,
+            OriginalParent,
+            currentChild,
+            currentParent,
+            PreserveCurrentWhenEmpty);
+
+    public static UiPixelRect Apply(
+        uint leftMode,
+        uint topMode,
+        uint rightMode,
+        uint bottomMode,
+        UiPixelRect originalChild,
+        UiPixelRect originalParent,
+        UiPixelRect currentChild,
+        UiPixelRect currentParent,
+        bool preserveCurrentWhenEmpty = false)
+    {
+        ValidateMode(leftMode, nameof(leftMode));
+        ValidateMode(topMode, nameof(topMode));
+        ValidateMode(rightMode, nameof(rightMode));
+        ValidateMode(bottomMode, nameof(bottomMode));
+
+        int deltaX = currentParent.Width - originalParent.Width;
+        int deltaY = currentParent.Height - originalParent.Height;
+        double scaleX = originalParent.Width != 0
+            ? (double)currentParent.Width / originalParent.Width
+            : 0d;
+        double scaleY = originalParent.Height != 0
+            ? (double)currentParent.Height / originalParent.Height
+            : 0d;
+
+        int x0 = ApplyNear(leftMode, originalChild.X0, originalChild.Width,
+            currentParent.Width, deltaX, scaleX);
+        int y0 = ApplyNear(topMode, originalChild.Y0, originalChild.Height,
+            currentParent.Height, deltaY, scaleY);
+        int x1 = ApplyFar(rightMode, originalChild.X1, originalChild.Width,
+            currentParent.Width, deltaX, scaleX);
+        int y1 = ApplyFar(bottomMode, originalChild.Y1, originalChild.Height,
+            currentParent.Height, deltaY, scaleY);
+
+        if (currentChild.Width != 0 || currentChild.Height != 0 || preserveCurrentWhenEmpty)
+        {
+            if (leftMode == 0) x0 = currentChild.X0;
+            if (topMode == 0) y0 = currentChild.Y0;
+            if (rightMode == 0) x1 = currentChild.X1;
+            if (bottomMode == 0) y1 = currentChild.Y1;
+        }
+
+        return new UiPixelRect(x0, y0, x1, y1);
+    }
+
+    private static int ApplyNear(
+        uint mode,
+        int originalEdge,
+        int originalSize,
+        int currentParentSize,
+        int parentDelta,
+        double scale)
+        => mode switch
+        {
+            2 => originalEdge + parentDelta,
+            3 => currentParentSize / 2 - originalSize / 2,
+            4 => (int)(originalEdge * scale),
+            _ => originalEdge,
+        };
+
+    private static int ApplyFar(
+        uint mode,
+        int originalEdge,
+        int originalSize,
+        int currentParentSize,
+        int parentDelta,
+        double scale)
+        => mode switch
+        {
+            1 => originalEdge + parentDelta,
+            3 => currentParentSize / 2 + originalSize / 2 - 1,
+            4 => (int)(originalEdge * scale),
+            _ => originalEdge,
+        };
+
+    private static void ValidateMode(uint mode, string parameterName)
+    {
+        if (mode > 4)
+            throw new ArgumentOutOfRangeException(parameterName, mode, "Retail edge mode must be in 0..4.");
+    }
+}