Add fancy tree control (#13426)

* Add fancy tree control

* inject dependencies

Content.Client/UserInterface/Controls/FancyTree/TreeLine.cs

@@ -0,0 +1,61 @@
+using Robust.Client.Graphics;
+using Robust.Client.UserInterface;
+using Robust.Shared.Utility;
+
+namespace Content.Client.UserInterface.Controls;
+
+/// <summary>
+///     This is a basic control that draws the lines connecting parents & children in a tree.
+/// </summary>
+/// <remarks>
+///     Ideally this would just be a draw method in <see cref="TreeItem"/>, but sadly the draw override gets called BEFORE children are drawn.
+/// </remarks>
+public sealed class TreeLine : Control
+{
+    protected override void Draw(DrawingHandleScreen handle)
+    {
+        base.Draw(handle);
+
+        // This is basically just a shitty hack to call Draw() after children get drawn.
+        if (Parent is not TreeItem parent)
+            return;
+
+        if (!parent.Expanded || !parent.Tree.DrawLines || parent.Body.ChildCount == 0)
+            return;
+
+        var width = Math.Max(1, (int) (parent.Tree.LineWidth * UIScale));
+        var w1 = width / 2;
+        var w2 = width - w1;
+
+        var global = parent.GlobalPixelPosition;
+
+        var iconPos = parent.Icon.GlobalPixelPosition - global;
+        var iconSize = parent.Icon.PixelSize;
+        var x = iconPos.X + iconSize.X / 2;
+        DebugTools.Assert(parent.Icon.Visible);
+
+        var buttonPos = parent.Button.GlobalPixelPosition - global;
+        var buttonSize = parent.Button.PixelSize;
+        var y1 = buttonPos.Y + buttonSize.Y;
+
+        var lastItem = (TreeItem) parent.Body.GetChild(parent.Body.ChildCount - 1);
+
+        var childPos = lastItem.Button.GlobalPixelPosition - global;
+        var y2 = childPos.Y + lastItem.Button.PixelSize.Y / 2;
+
+        // Vertical line
+        var rect = new UIBox2i((x - w1, y1), (x + w2, y2));
+        handle.DrawRect(rect, parent.Tree.LineColor);
+
+        // Horizontal lines
+        var dx = Math.Max(1, (int) (FancyTree.Indentation * UIScale / 2));
+        foreach (var child in parent.Body.Children)
+        {
+            var item = (TreeItem) child;
+            var pos = item.Button.GlobalPixelPosition - global;
+            var y = pos.Y + item.Button.PixelSize.Y / 2;
+            rect = new UIBox2i((x - w1, y - w1), (x + dx, y + w2));
+            handle.DrawRect(rect, parent.Tree.LineColor);
+        }
+    }
+}