gui-cs.Terminal.Gui/Terminal.Gui/View/Layout/ViewLayout.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Diagnostics;
using System.Linq;

namespace Terminal.Gui;

/// <summary>
///         <para>
///         Indicates the LayoutStyle for the <see cref="View"/>.
///         </para>
///         <para>
///         If Absolute, the <see cref="View.X"/>, <see cref="View.Y"/>, <see cref="View.Width"/>, and
///         <see cref="View.Height"/>
///         objects are all absolute values and are not relative. The position and size of the view is described by
///         <see cref="View.Frame"/>.
///         </para>
///         <para>
///         If Computed, one or more of the <see cref="View.X"/>, <see cref="View.Y"/>, <see cref="View.Width"/>, or
///         <see cref="View.Height"/>
///         objects are relative to the <see cref="View.SuperView"/> and are computed at layout time.
///         </para>
/// </summary>
public enum LayoutStyle {
	/// <summary>
	/// Indicates the <see cref="View.X"/>, <see cref="View.Y"/>, <see cref="View.Width"/>, and <see cref="View.Height"/>
	/// objects are all absolute values and are not relative. The position and size of the view is described by
	/// <see cref="View.Frame"/>.
	/// </summary>
	Absolute,

	/// <summary>
	/// Indicates one or more of the <see cref="View.X"/>, <see cref="View.Y"/>, <see cref="View.Width"/>, or
	/// <see cref="View.Height"/>
	/// objects are relative to the <see cref="View.SuperView"/> and are computed at layout time.  The position and size of the
	/// view
	/// will be computed based on these objects at layout time. <see cref="View.Frame"/> will provide the absolute computed
	/// values.
	/// </summary>
	Computed
}

public partial class View {
	bool _autoSize;
	Rect _frame;
	Dim _height = Dim.Sized (0);
	Dim _width = Dim.Sized (0);
	Pos _x = Pos.At (0);
	Pos _y = Pos.At (0);

	/// <summary>
	/// Gets or sets the absolute location and dimension of the view.
	/// </summary>
	/// <value>
	/// The rectangle describing absolute location and dimension of the view,
	/// in coordinates relative to the <see cref="SuperView"/>'s <see cref="Bounds"/>.
	/// </value>
	/// <remarks>
	///         <para>
	///         Frame is relative to the <see cref="SuperView"/>'s <see cref="Bounds"/>.
	///         </para>
	///         <para>
	///         Setting Frame will set <see cref="X"/>, <see cref="Y"/>, <see cref="Width"/>, and <see cref="Height"/>
	///         to the values of the corresponding properties of the <paramref name="value"/> parameter.
	///         </para>
	///         <para>
	///         This causes <see cref="LayoutStyle"/> to be <see cref="LayoutStyle.Absolute"/>.
	///         </para>
	///         <para>
	///         Altering the Frame will eventually (when the view hierarchy is next laid out via  see cref="LayoutSubviews"/>)
	///         cause <see cref="LayoutSubview(View, Rect)"/> and <see cref="OnDrawContent(Rect)"/> methods to be called.
	///         </para>
	/// </remarks>
	public Rect Frame {
		get => _frame;
		set {
			_frame = new Rect (value.X, value.Y, Math.Max (value.Width, 0), Math.Max (value.Height, 0));

			// If Frame gets set, by definition, the View is now LayoutStyle.Absolute, so
			// set all Pos/Dim to Absolute values.
			_x = _frame.X;
			_y = _frame.Y;
			_width = _frame.Width;
			_height = _frame.Height;

			// TODO: Figure out if the below can be optimized.
			if (IsInitialized /*|| LayoutStyle == LayoutStyle.Absolute*/) {
				LayoutFrames ();
				SetTextFormatterSize ();
				SetNeedsLayout ();
				SetNeedsDisplay ();
			}
		}
	}

	/// <summary>
	/// The frame (specified as a <see cref="Thickness"/>) that separates a View from other SubViews of the same SuperView.
	/// The margin offsets the <see cref="Bounds"/> from the <see cref="Frame"/>.
	/// </summary>
	/// <remarks>
	///         <para>
	///         The frames (<see cref="Margin"/>, <see cref="Border"/>, and <see cref="Padding"/>) are not part of the View's
	///         content
	///         and are not clipped by the View's Clip Area.
	///         </para>
	///         <para>
	///         Changing the size of a frame (<see cref="Margin"/>, <see cref="Border"/>, or <see cref="Padding"/>)
	///         will change the size of the <see cref="Frame"/> and trigger <see cref="LayoutSubviews"/> to update the layout
	///         of the
	///         <see cref="SuperView"/> and its <see cref="Subviews"/>.
	///         </para>
	/// </remarks>
	public Frame Margin { get; private set; }

	/// <summary>
	/// The frame (specified as a <see cref="Thickness"/>) inside of the view that offsets the <see cref="Bounds"/> from the
	/// <see cref="Margin"/>.
	/// The Border provides the space for a visual border (drawn using line-drawing glyphs) and the Title.
	/// The Border expands inward; in other words if `Border.Thickness.Top == 2` the border and
	/// title will take up the first row and the second row will be filled with spaces.
	/// </summary>
	/// <remarks>
	///         <para>
	///         <see cref="BorderStyle"/> provides a simple helper for turning a simple border frame on or off.
	///         </para>
	///         <para>
	///         The frames (<see cref="Margin"/>, <see cref="Border"/>, and <see cref="Padding"/>) are not part of the View's
	///         content
	///         and are not clipped by the View's Clip Area.
	///         </para>
	///         <para>
	///         Changing the size of a frame (<see cref="Margin"/>, <see cref="Border"/>, or <see cref="Padding"/>)
	///         will change the size of the <see cref="Frame"/> and trigger <see cref="LayoutSubviews"/> to update the layout
	///         of the
	///         <see cref="SuperView"/> and its <see cref="Subviews"/>.
	///         </para>
	/// </remarks>
	public Frame Border { get; private set; }

	/// <summary>
	/// Gets or sets whether the view has a one row/col thick border.
	/// </summary>
	/// <remarks>
	///         <para>
	///         This is a helper for manipulating the view's <see cref="Border"/>. Setting this property to any value other
	///         than
	///         <see cref="LineStyle.None"/> is equivalent to setting <see cref="Border"/>'s <see cref="Frame.Thickness"/>
	///         to `1` and <see cref="BorderStyle"/> to the value.
	///         </para>
	///         <para>
	///         Setting this property to <see cref="LineStyle.None"/> is equivalent to setting <see cref="Border"/>'s
	///         <see cref="Frame.Thickness"/>
	///         to `0` and <see cref="BorderStyle"/> to <see cref="LineStyle.None"/>.
	///         </para>
	///         <para>
	///         For more advanced customization of the view's border, manipulate see <see cref="Border"/> directly.
	///         </para>
	/// </remarks>
	public LineStyle BorderStyle {
		get => Border?.BorderStyle ?? LineStyle.None;
		set {
			if (Border == null) {
				throw new InvalidOperationException ("Border is null; this is likely a bug.");
			}
			if (value != LineStyle.None) {
				Border.Thickness = new Thickness (1);
			} else {
				Border.Thickness = new Thickness (0);
			}
			Border.BorderStyle = value;
			LayoutFrames ();
			SetNeedsLayout ();
		}
	}

	/// <summary>
	/// The frame (specified as a <see cref="Thickness"/>) inside of the view that offsets the <see cref="Bounds"/> from the
	/// <see cref="Border"/>.
	/// </summary>
	/// <remarks>
	///         <para>
	///         The frames (<see cref="Margin"/>, <see cref="Border"/>, and <see cref="Padding"/>) are not part of the View's
	///         content
	///         and are not clipped by the View's Clip Area.
	///         </para>
	///         <para>
	///         Changing the size of a frame (<see cref="Margin"/>, <see cref="Border"/>, or <see cref="Padding"/>)
	///         will change the size of the <see cref="Frame"/> and trigger <see cref="LayoutSubviews"/> to update the layout
	///         of the
	///         <see cref="SuperView"/> and its <see cref="Subviews"/>.
	///         </para>
	/// </remarks>
	public Frame Padding { get; private set; }

	/// <summary>
	///         <para>
	///         Gets the LayoutStyle for the <see cref="View"/>.
	///         </para>
	///         <para>
	///         If Absolute, the <see cref="View.X"/>, <see cref="View.Y"/>, <see cref="View.Width"/>, and
	///         <see cref="View.Height"/>
	///         objects are all absolute values and are not relative. The position and size of the view is described by
	///         <see cref="View.Frame"/>.
	///         </para>
	///         <para>
	///         If Computed, one or more of the <see cref="View.X"/>, <see cref="View.Y"/>, <see cref="View.Width"/>, or
	///         <see cref="View.Height"/>
	///         objects are relative to the <see cref="View.SuperView"/> and are computed at layout time.
	///         </para>
	/// </summary>
	/// <value>The layout style.</value>
	public LayoutStyle LayoutStyle {
		get {
			if (_x is Pos.PosAbsolute && _y is Pos.PosAbsolute && _width is Dim.DimAbsolute && _height is Dim.DimAbsolute) {
				return LayoutStyle.Absolute;
			}
			return LayoutStyle.Computed;
		}
	}

	/// <summary>
	/// The bounds represent the View-relative rectangle used for this view; the area inside of the view where subviews and
	/// content are presented.
	/// </summary>
	/// <value>The rectangle describing the location and size of the area where the views' subviews and content are drawn.</value>
	/// <remarks>
	///         <para>
	///         If <see cref="LayoutStyle"/> is <see cref="LayoutStyle.Computed"/> the value of Bounds is indeterminate until
	///         the view has been initialized (<see cref="IsInitialized"/> is true) and <see cref="LayoutSubviews"/> has been
	///         called.
	///         </para>
	///         <para>
	///         Updates to the Bounds updates <see cref="Frame"/>, and has the same effect as updating the
	///         <see cref="Frame"/>.
	///         </para>
	///         <para>
	///         Altering the Bounds will eventually (when the view is next laid out) cause the
	///         <see cref="LayoutSubview(View, Rect)"/>
	///         and <see cref="OnDrawContent(Rect)"/> methods to be called.
	///         </para>
	///         <para>
	///         Because <see cref="Bounds"/> coordinates are relative to the upper-left corner of the <see cref="View"/>,
	///         the coordinates of the upper-left corner of the rectangle returned by this property are (0,0).
	///         Use this property to obtain the size of the area of the view for tasks such as drawing the view's contents.
	///         </para>
	/// </remarks>
	public virtual Rect Bounds {
		get {
#if DEBUG
			if (LayoutStyle == LayoutStyle.Computed && !IsInitialized) {
				Debug.WriteLine ($"WARNING: Bounds is being accessed before the View has been initialized. This is likely a bug in {this}");
			}
#endif // DEBUG
			var frameRelativeBounds = FrameGetInsideBounds ();
			return new Rect (default, frameRelativeBounds.Size);
		}
		set {
			// TODO: Should we enforce Bounds.X/Y == 0? The code currently ignores value.X/Y which is
			// TODO: correct behavior, but is silent. Perhaps an exception?
#if DEBUG
			if (value.Location != Point.Empty) {
				Debug.WriteLine ($"WARNING: Bounds.Location must always be 0,0. Location ({value.Location}) is ignored. {this}");
			}
#endif // DEBUG
			Frame = new Rect (Frame.Location,
				new Size (
					value.Size.Width + Margin.Thickness.Horizontal + Border.Thickness.Horizontal + Padding.Thickness.Horizontal,
					value.Size.Height + Margin.Thickness.Vertical + Border.Thickness.Vertical + Padding.Thickness.Vertical
				)
			);
		}
	}

	/// <summary>
	/// Gets or sets the X position for the view (the column).
	/// </summary>
	/// <value>The <see cref="Pos"/> object representing the X position.</value>
	/// <remarks>
	///         <para>
	///         If set to a relative value (e.g. <see cref="Pos.Center"/>) the value is indeterminate until the
	///         view has been initialized (<see cref="IsInitialized"/> is true) and <see cref="SetRelativeLayout(Rect)"/> has been
	///         called.
	///         </para>
	///         <para>
	///         Changing this property will eventually (when the view is next drawn) cause the
	///          <see cref="LayoutSubview(View, Rect)"/> and
	///         <see cref="OnDrawContent(Rect)"/> methods to be called.
	///         </para>
	///         <para>
	///         Changing this property will cause <see cref="Frame"/> to be updated. If
	///         the new value is not of type <see cref="Pos.PosAbsolute"/> the <see cref="LayoutStyle"/> will change to
	///         <see cref="LayoutStyle.Computed"/>.
	///         </para>
	///         <para>
	///         The default value is <c>Pos.At (0)</c>.
	///         </para>
	/// </remarks>
	public Pos X {
		get => VerifyIsInitialized (_x, nameof (X));
		set {
			_x = value ?? throw new ArgumentNullException (nameof (value), @$"{nameof (X)} cannot be null");
			OnResizeNeeded ();
		}
	}

	/// <summary>
	/// Gets or sets the Y position for the view (the row).
	/// </summary>
	/// <value>The <see cref="Pos"/> object representing the Y position.</value>
	/// <remarks>
	///         <para>
	///         If set to a relative value (e.g. <see cref="Pos.Center"/>) the value is indeterminate until the
	///         view has been initialized (<see cref="IsInitialized"/> is true) and <see cref="SetRelativeLayout(Rect)"/> has been
	///         called.
	///         </para>
	///         <para>
	///         Changing this property will eventually (when the view is next drawn) cause the
	///         <see cref="LayoutSubview(View, Rect)"/> and
	///         <see cref="OnDrawContent(Rect)"/> methods to be called.
	///         </para>
	///         <para>
	///         Changing this property will cause <see cref="Frame"/> to be updated. If
	///         the new value is not of type <see cref="Pos.PosAbsolute"/> the <see cref="LayoutStyle"/> will change to
	///         <see cref="LayoutStyle.Computed"/>.
	///         </para>
	///         <para>
	///         The default value is <c>Pos.At (0)</c>.
	///         </para>
	/// </remarks>
	public Pos Y {
		get => VerifyIsInitialized (_y, nameof (Y));
		set {
			_y = value ?? throw new ArgumentNullException (nameof (value), @$"{nameof (Y)} cannot be null");
			OnResizeNeeded ();
		}
	}

	/// <summary>
	/// Gets or sets the width dimension of the view.
	/// </summary>
	/// <value>The <see cref="Dim"/> object representing the width of the view (the number of columns).</value>
	/// <remarks>
	///         <para>
	///         If set to a relative value (e.g. <see cref="Dim.Fill(int)"/>) the value is indeterminate until the
	///         view has been initialized (<see cref="IsInitialized"/> is true) and <see cref="SetRelativeLayout(Rect)"/> has been
	///         called.
	///         </para>
	///         <para>
	///         Changing this property will eventually (when the view is next drawn) cause the
	///         <see cref="LayoutSubview(View, Rect)"/>
	///         and <see cref="OnDrawContent(Rect)"/> methods to be called.
	///         </para>
	///         <para>
	///         Changing this property will cause <see cref="Frame"/> to be updated. If
	///         the new value is not of type <see cref="Dim.DimAbsolute"/> the <see cref="LayoutStyle"/> will change to
	///         <see cref="LayoutStyle.Computed"/>.
	///         </para>
	///         <para>
	///         The default value is <c>Dim.Sized (0)</c>.
	///         </para>
	/// </remarks>
	public Dim Width {
		get => VerifyIsInitialized (_width, nameof (Width));
		set {
			_width = value ?? throw new ArgumentNullException (nameof (value), @$"{nameof (Width)} cannot be null");

			if (ValidatePosDim) {
				var isValidNewAutSize = AutoSize && IsValidAutoSizeWidth (_width);

				if (IsAdded && AutoSize && !isValidNewAutSize) {
					throw new InvalidOperationException ("Must set AutoSize to false before set the Width.");
				}
			}
			OnResizeNeeded ();
		}
	}

	/// <summary>
	/// Gets or sets the height dimension of the view.
	/// </summary>
	/// <value>The <see cref="Dim"/> object representing the height of the view (the number of rows).</value>
	/// <remarks>
	///         <para>
	///         If set to a relative value (e.g. <see cref="Dim.Fill(int)"/>) the value is indeterminate until the
	///         view has been initialized (<see cref="IsInitialized"/> is true) and <see cref="SetRelativeLayout(Rect)"/> has been
	///         called.
	///         </para>
	///         <para>
	///         Changing this property will eventually (when the view is next drawn) cause the
	///         <see cref="LayoutSubview(View, Rect)"/>
	///         and <see cref="OnDrawContent(Rect)"/> methods to be called.
	///         </para>
	///         <para>
	///         Changing this property will cause <see cref="Frame"/> to be updated. If
	///         the new value is not of type <see cref="Dim.DimAbsolute"/> the <see cref="LayoutStyle"/> will change to
	///         <see cref="LayoutStyle.Computed"/>.
	///         </para>
	///         <para>
	///         The default value is <c>Dim.Sized (0)</c>.
	///         </para>
	/// </remarks>
	public Dim Height {
		get => VerifyIsInitialized (_height, nameof (Height));
		set {
			_height = value ?? throw new ArgumentNullException (nameof (value), @$"{nameof (Height)} cannot be null");

			if (ValidatePosDim) {
				var isValidNewAutSize = AutoSize && IsValidAutoSizeHeight (_height);

				if (IsAdded && AutoSize && !isValidNewAutSize) {
					throw new InvalidOperationException ("Must set AutoSize to false before setting the Height.");
				}
			}
			OnResizeNeeded ();
		}
	}

	/// <summary>
	/// Gets or sets whether validation of <see cref="Pos"/> and <see cref="Dim"/> occurs.
	/// </summary>
	/// <remarks>
	/// Setting this to <see langword="true"/> will enable validation of <see cref="X"/>, <see cref="Y"/>, <see cref="Width"/>,
	/// and <see cref="Height"/>
	/// during set operations and in <see cref="LayoutSubviews"/>. If invalid settings are discovered exceptions will be thrown
	/// indicating the error.
	/// This will impose a performance penalty and thus should only be used for debugging.
	/// </remarks>
	public bool ValidatePosDim { get; set; }

	internal bool LayoutNeeded { get; private set; } = true;

	/// <summary>
	/// Gets or sets a flag that determines whether the View will be automatically resized to fit the <see cref="Text"/>
	/// within <see cref="Bounds"/>.
	/// <para>
	/// The default is <see langword="false"/>. Set to <see langword="true"/> to turn on AutoSize. If <see langword="true"/>
	/// then
	/// <see cref="Width"/> and <see cref="Height"/> will be used if <see cref="Text"/> can fit;
	/// if <see cref="Text"/> won't fit the view will be resized as needed.
	/// </para>
	/// <para>
	/// If <see cref="AutoSize"/> is set to <see langword="true"/> then <see cref="Width"/> and <see cref="Height"/>
	/// will be changed to <see cref="Dim.DimAbsolute"/> if they are not already.
	/// </para>
	/// <para>
	/// If <see cref="AutoSize"/> is set to <see langword="false"/> then <see cref="Width"/> and <see cref="Height"/>
	/// will left unchanged.
	/// </para>
	/// </summary>
	public virtual bool AutoSize {
		get => _autoSize;
		set {
			var v = ResizeView (value);
			TextFormatter.AutoSize = v;
			if (_autoSize != v) {
				_autoSize = v;
				TextFormatter.NeedsFormat = true;
				UpdateTextFormatterText ();
				OnResizeNeeded ();
			}
		}
	}

	/// <summary>
	/// Event called only once when the <see cref="View"/> is being initialized for the first time.
	/// Allows configurations and assignments to be performed before the <see cref="View"/> being shown.
	/// This derived from <see cref="ISupportInitializeNotification"/> to allow notify all the views that are being
	/// initialized.
	/// </summary>
	public event EventHandler Initialized;

	/// <summary>
	/// Helper to get the total thickness of the <see cref="Margin"/>, <see cref="Border"/>, and <see cref="Padding"/>.
	/// </summary>
	/// <returns>A thickness that describes the sum of the Frames' thicknesses.</returns>
	public Thickness GetFramesThickness ()
	{
		var left = Margin.Thickness.Left + Border.Thickness.Left + Padding.Thickness.Left;
		var top = Margin.Thickness.Top + Border.Thickness.Top + Padding.Thickness.Top;
		var right = Margin.Thickness.Right + Border.Thickness.Right + Padding.Thickness.Right;
		var bottom = Margin.Thickness.Bottom + Border.Thickness.Bottom + Padding.Thickness.Bottom;
		return new Thickness (left, top, right, bottom);
	}

	/// <summary>
	/// Helper to get the X and Y offset of the Bounds from the Frame. This is the sum of the Left and Top properties of
	/// <see cref="Margin"/>, <see cref="Border"/> and <see cref="Padding"/>.
	/// </summary>
	public Point GetBoundsOffset () => new (Padding?.Thickness.GetInside (Padding.Frame).X ?? 0, Padding?.Thickness.GetInside (Padding.Frame).Y ?? 0);

	/// <summary>
	/// Creates the view's <see cref="Frame"/> objects. This internal method is overridden by Frame to do nothing
	/// to prevent recursion during View construction.
	/// </summary>
	internal virtual void CreateFrames ()
	{
		void ThicknessChangedHandler (object sender, EventArgs e)
		{
			if (IsInitialized) {
				LayoutFrames ();
			}
			SetNeedsLayout ();
			SetNeedsDisplay ();
		}

		if (Margin != null) {
			Margin.ThicknessChanged -= ThicknessChangedHandler;
			Margin.Dispose ();
		}
		Margin = new Frame { Id = "Margin", Thickness = new Thickness (0) };
		Margin.ThicknessChanged += ThicknessChangedHandler;
		Margin.Parent = this;

		if (Border != null) {
			Border.ThicknessChanged -= ThicknessChangedHandler;
			Border.Dispose ();
		}
		Border = new Frame { Id = "Border", Thickness = new Thickness (0) };
		Border.ThicknessChanged += ThicknessChangedHandler;
		Border.Parent = this;

		// TODO: Create View.AddAdornment

		if (Padding != null) {
			Padding.ThicknessChanged -= ThicknessChangedHandler;
			Padding.Dispose ();
		}
		Padding = new Frame { Id = "Padding", Thickness = new Thickness (0) };
		Padding.ThicknessChanged += ThicknessChangedHandler;
		Padding.Parent = this;
	}

	Rect FrameGetInsideBounds ()
	{
		if (Margin == null || Border == null || Padding == null) {
			return new Rect (default, Frame.Size);
		}
		var width = Math.Max (0,  Frame.Size.Width - Margin.Thickness.Horizontal - Border.Thickness.Horizontal - Padding.Thickness.Horizontal);
		var height = Math.Max (0, Frame.Size.Height - Margin.Thickness.Vertical - Border.Thickness.Vertical - Padding.Thickness.Vertical);
		return new Rect (Point.Empty, new Size (width, height));
	}

	// Diagnostics to highlight when X or Y is read before the view has been initialized
	Pos VerifyIsInitialized (Pos pos, string member)
	{
#if DEBUG
		if (LayoutStyle == LayoutStyle.Computed && !IsInitialized) {
			Debug.WriteLine ($"WARNING: \"{this}\" has not been initialized; {member} is indeterminate {pos}. This is potentially a bug.");
		}
#endif // DEBUG
		return pos;
	}

	// Diagnostics to highlight when Width or Height is read before the view has been initialized
	Dim VerifyIsInitialized (Dim dim, string member)
	{
#if DEBUG
		if (LayoutStyle == LayoutStyle.Computed && !IsInitialized) {
			Debug.WriteLine ($"WARNING: \"{this}\" has not been initialized; {member} is indeterminate: {dim}. This is potentially a bug.");
		}
#endif // DEBUG		
		return dim;
	}

	/// <summary>
	/// Called whenever the view needs to be resized. Sets <see cref="Frame"/> and triggers a <see cref="LayoutSubviews()"/>
	/// call.
	/// </summary>
	/// <remarks>
	///         <para>
	///         Sets the <see cref="Frame"/>.
	///         </para>
	///         <para>
	///         Can be overridden if the view resize behavior is different than the default.
	///         </para>
	/// </remarks>
	protected virtual void OnResizeNeeded ()
	{
		// First try SuperView.Bounds, then Application.Top, then Driver.Bounds.
		// Finally, if none of those are valid, use int.MaxValue (for Unit tests).
		var relativeBounds = SuperView is { IsInitialized: true }        ? SuperView.Bounds :
			Application.Top != null && Application.Top.IsInitialized ? Application.Top.Bounds :
										   Application.Driver?.Bounds ??
										   new Rect (0, 0, int.MaxValue, int.MaxValue);
		SetRelativeLayout (relativeBounds);

		// TODO: Determine what, if any of the below is actually needed here.
		if (IsInitialized) {
			SetFrameToFitText ();
			LayoutFrames ();
			SetTextFormatterSize ();
			SetNeedsLayout ();
			SetNeedsDisplay ();
		}
	}

	/// <summary>
	/// Sets the internal <see cref="LayoutNeeded"/> flag for this View and all of it's
	/// subviews and it's SuperView. The main loop will call SetRelativeLayout and LayoutSubviews
	/// for any view with <see cref="LayoutNeeded"/> set.
	/// </summary>
	internal void SetNeedsLayout ()
	{
		if (LayoutNeeded) {
			return;
		}
		LayoutNeeded = true;
		foreach (var view in Subviews) {
			view.SetNeedsLayout ();
		}
		TextFormatter.NeedsFormat = true;
		SuperView?.SetNeedsLayout ();
	}

	/// <summary>
	/// Indicates that the view does not need to be laid out.
	/// </summary>
	protected void ClearLayoutNeeded () => LayoutNeeded = false;

	/// <summary>
	/// Converts a screen-relative coordinate to a Frame-relative coordinate. Frame-relative means
	/// relative to the View's <see cref="SuperView"/>'s <see cref="Bounds"/>.
	/// </summary>
	/// <returns>The coordinate relative to the <see cref="SuperView"/>'s <see cref="Bounds"/>.</returns>
	/// <param name="x">Screen-relative column.</param>
	/// <param name="y">Screen-relative row.</param>
	public Point ScreenToFrame (int x, int y)
	{
		var superViewBoundsOffset = SuperView?.GetBoundsOffset () ?? Point.Empty;
		var ret = new Point (x - Frame.X - superViewBoundsOffset.X, y - Frame.Y - superViewBoundsOffset.Y);
		if (SuperView != null) {
			var superFrame = SuperView.ScreenToFrame (x - superViewBoundsOffset.X, y - superViewBoundsOffset.Y);
			ret = new Point (superFrame.X - Frame.X, superFrame.Y - Frame.Y);
		}
		return ret;
	}

	/// <summary>
	/// Converts a screen-relative coordinate to a bounds-relative coordinate.
	/// </summary>
	/// <returns>The coordinate relative to this view's <see cref="Bounds"/>.</returns>
	/// <param name="x">Screen-relative column.</param>
	/// <param name="y">Screen-relative row.</param>
	public Point ScreenToBounds (int x, int y)
	{
		var screen = ScreenToFrame (x, y);
		var boundsOffset = GetBoundsOffset ();
		return new Point (screen.X - boundsOffset.X, screen.Y - boundsOffset.Y);
	}

	/// <summary>
	/// Converts a <see cref="Bounds"/>-relative coordinate to a screen-relative coordinate. The output is optionally clamped
	/// to the screen dimensions.
	/// </summary>
	/// <param name="x"><see cref="Bounds"/>-relative column.</param>
	/// <param name="y"><see cref="Bounds"/>-relative row.</param>
	/// <param name="rx">Absolute column; screen-relative.</param>
	/// <param name="ry">Absolute row; screen-relative.</param>
	/// <param name="clamped">
	/// If <see langword="true"/>, <paramref name="rx"/> and <paramref name="ry"/> will be clamped to the
	/// screen dimensions (will never be negative and will always be less than <see cref="ConsoleDriver.Cols"/> and
	/// <see cref="ConsoleDriver.Rows"/>, respectively.
	/// </param>
	public virtual void BoundsToScreen (int x, int y, out int rx, out int ry, bool clamped = true)
	{
		var boundsOffset = GetBoundsOffset ();
		rx = x + Frame.X + boundsOffset.X;
		ry = y + Frame.Y + boundsOffset.Y;

		var super = SuperView;
		while (super != null) {
			boundsOffset = super.GetBoundsOffset ();
			rx += super.Frame.X + boundsOffset.X;
			ry += super.Frame.Y + boundsOffset.Y;
			super = super.SuperView;
		}

		// The following ensures that the cursor is always in the screen boundaries.
		if (clamped) {
			ry = Math.Min (ry, Driver.Rows - 1);
			rx = Math.Min (rx, Driver.Cols - 1);
		}
	}

	/// <summary>
	/// Converts a <see cref="Bounds"/>-relative region to a screen-relative region.
	/// </summary>
	public Rect BoundsToScreen (Rect region)
	{
		BoundsToScreen (region.X, region.Y, out var x, out var y, false);
		return new Rect (x, y, region.Width, region.Height);
	}

	/// <summary>
	/// Gets the <see cref="Frame"/> with a screen-relative location.
	/// </summary>
	/// <returns>The location and size of the view in screen-relative coordinates.</returns>
	public virtual Rect FrameToScreen ()
	{
		var ret = Frame;
		var super = SuperView;
		while (super != null) {
			var boundsOffset = super.GetBoundsOffset ();
			ret.X += super.Frame.X + boundsOffset.X;
			ret.Y += super.Frame.Y + boundsOffset.Y;
			super = super.SuperView;
		}
		return ret;
	}

	/// <summary>
	/// Applies the view's position (<see cref="X"/>, <see cref="Y"/>) and dimension (<see cref="Width"/>, and
	/// <see cref="Height"/>) to
	/// <see cref="Frame"/>, given a rectangle describing the SuperView's Bounds (nominally the same as
	/// <c>this.SuperView.Bounds</c>).
	/// </summary>
	/// <param name="superviewBounds">
	/// The rectangle describing the SuperView's Bounds (nominally the same as
	/// <c>this.SuperView.Bounds</c>).
	/// </param>
	internal void SetRelativeLayout (Rect superviewBounds)
	{
		Debug.Assert (_x != null);
		Debug.Assert (_y != null);
		Debug.Assert (_width != null);
		Debug.Assert (_height != null);

		int newX, newW, newY, newH;
		var autosize = Size.Empty;

		if (AutoSize) {
			// Note this is global to this function and used as such within the local functions defined
			// below. In v2 AutoSize will be re-factored to not need to be dealt with in this function.
			autosize = GetAutoSize ();
		}

		// TODO: Since GetNewLocationAndDimension does not depend on View, it can be moved into PosDim.cs
		// TODO: to make architecture more clean. Do this after DimAuto is implemented and the 
		// TODO: View.AutoSize stuff is removed.

		// Returns the new dimension (width or height) and location (x or y) for the View given
		//   the superview's Bounds
		//   the current Pos (View.X or View.Y)
		//   the current Dim (View.Width or View.Height)
		// This method is called recursively if pos is Pos.PosCombine
		(int newLocation, int newDimension) GetNewLocationAndDimension (bool width, Rect superviewBounds, Pos pos, Dim dim, int autosizeDimension)
		{
			// Gets the new dimension (width or height, dependent on `width`) of the given Dim given:
			//   location: the current location (x or y)
			//   dimension: the new dimension (width or height) (if relevant for Dim type)
			//   autosize: the size to use if autosize = true
			// This method is recursive if d is Dim.DimCombine
			int GetNewDimension (Dim d, int location, int dimension, int autosize)
			{
				int newDimension;
				switch (d) {

				case Dim.DimCombine combine:
					// TODO: Move combine logic into DimCombine?
					var leftNewDim = GetNewDimension (combine._left,   location, dimension, autosize);
					var rightNewDim = GetNewDimension (combine._right, location, dimension, autosize);
					if (combine._add) {
						newDimension = leftNewDim + rightNewDim;
					} else {
						newDimension = leftNewDim - rightNewDim;
					}
					newDimension = AutoSize && autosize > newDimension ? autosize : newDimension;
					break;

				case Dim.DimFactor factor when !factor.IsFromRemaining ():
					newDimension = d.Anchor (dimension);
					newDimension = AutoSize && autosize > newDimension ? autosize : newDimension;
					break;

				case Dim.DimAbsolute:
					// DimAbsoulte.Anchor (int width) ignores width and returns n
					newDimension = Math.Max (d.Anchor (0), 0);
					newDimension = AutoSize && autosize > newDimension ? autosize : newDimension;
					break;

				case Dim.DimFill:
				default:
					newDimension = Math.Max (d.Anchor (dimension - location), 0);
					newDimension = AutoSize && autosize > newDimension ? autosize : newDimension;
					break;
				}

				return newDimension;
			}

			int newDimension, newLocation;
			var superviewDimension = width ? superviewBounds.Width : superviewBounds.Height;

			// Determine new location
			switch (pos) {
			case Pos.PosCenter posCenter:
				// For Center, the dimension is dependent on location, but we need to force getting the dimension first
				// using a location of 0
				newDimension = Math.Max (GetNewDimension (dim, 0, superviewDimension, autosizeDimension), 0);
				newLocation = posCenter.Anchor (superviewDimension - newDimension);
				newDimension = Math.Max (GetNewDimension (dim, newLocation, superviewDimension, autosizeDimension), 0);
				break;

			case Pos.PosCombine combine:
				// TODO: Move combine logic into PosCombine?
				int left, right;
				(left, newDimension) = GetNewLocationAndDimension (width,  superviewBounds, combine._left,  dim, autosizeDimension);
				(right, newDimension) = GetNewLocationAndDimension (width, superviewBounds, combine._right, dim, autosizeDimension);
				if (combine._add) {
					newLocation = left + right;
				} else {
					newLocation = left - right;
				}
				newDimension = Math.Max (GetNewDimension (dim, newLocation, superviewDimension, autosizeDimension), 0);
				break;

			case Pos.PosAnchorEnd:
			case Pos.PosAbsolute:
			case Pos.PosFactor:
			case Pos.PosFunc:
			case Pos.PosView:
			default:
				newLocation = pos?.Anchor (superviewDimension) ?? 0;
				newDimension = Math.Max (GetNewDimension (dim, newLocation, superviewDimension, autosizeDimension), 0);
				break;
			}


			return (newLocation, newDimension);
		}

		// horizontal/width
		(newX, newW) = GetNewLocationAndDimension (true, superviewBounds, _x, _width, autosize.Width);

		// vertical/height
		(newY, newH) = GetNewLocationAndDimension (false, superviewBounds, _y, _height, autosize.Height);

		var r = new Rect (newX, newY, newW, newH);
		if (Frame != r) {
			// Set the frame. Do NOT use `Frame` as it overwrites X, Y, Width, and Height, making
			// the view LayoutStyle.Absolute.
			_frame = r;
			if (_x is Pos.PosAbsolute) {
				_x = Frame.X;
			}
			if (_y is Pos.PosAbsolute) {
				_y = Frame.Y;
			}
			if (_width is Dim.DimAbsolute) {
				_width = Frame.Width;
			}
			if (_height is Dim.DimAbsolute) {
				_height = Frame.Height;
			}

			if (IsInitialized) {
				// TODO: Figure out what really is needed here. All unit tests (except AutoSize) pass as-is
				//LayoutFrames ();
				SetTextFormatterSize ();
				SetNeedsLayout ();
				//SetNeedsDisplay ();
			}

			// BUGBUG: Why is this AFTER setting Frame? Seems duplicative.
			if (!SetFrameToFitText ()) {
				SetTextFormatterSize ();
			}
		}
	}

	/// <summary>
	/// Fired after the View's <see cref="LayoutSubviews"/> method has completed.
	/// </summary>
	/// <remarks>
	/// Subscribe to this event to perform tasks when the <see cref="View"/> has been resized or the layout has otherwise
	/// changed.
	/// </remarks>
	public event EventHandler<LayoutEventArgs> LayoutStarted;

	/// <summary>
	/// Raises the <see cref="LayoutStarted"/> event. Called from  <see cref="LayoutSubviews"/> before any subviews have been
	/// laid out.
	/// </summary>
	internal virtual void OnLayoutStarted (LayoutEventArgs args) => LayoutStarted?.Invoke (this, args);

	/// <summary>
	/// Fired after the View's <see cref="LayoutSubviews"/> method has completed.
	/// </summary>
	/// <remarks>
	/// Subscribe to this event to perform tasks when the <see cref="View"/> has been resized or the layout has otherwise
	/// changed.
	/// </remarks>
	public event EventHandler<LayoutEventArgs> LayoutComplete;

	/// <summary>
	/// Raises the <see cref="LayoutComplete"/> event. Called from  <see cref="LayoutSubviews"/> before all sub-views have been
	/// laid out.
	/// </summary>
	internal virtual void OnLayoutComplete (LayoutEventArgs args) => LayoutComplete?.Invoke (this, args);

	internal void CollectPos (Pos pos, View from, ref HashSet<View> nNodes, ref HashSet<(View, View)> nEdges)
	{
		switch (pos) {
		case Pos.PosView pv:
			// See #2461
			//if (!from.InternalSubviews.Contains (pv.Target)) {
			//	throw new InvalidOperationException ($"View {pv.Target} is not a subview of {from}");
			//}
			if (pv.Target != this) {
				nEdges.Add ((pv.Target, from));
			}
			return;
		case Pos.PosCombine pc:
			CollectPos (pc._left,  from, ref nNodes, ref nEdges);
			CollectPos (pc._right, from, ref nNodes, ref nEdges);
			break;
		}
	}

	internal void CollectDim (Dim dim, View from, ref HashSet<View> nNodes, ref HashSet<(View, View)> nEdges)
	{
		switch (dim) {
		case Dim.DimView dv:
			// See #2461
			//if (!from.InternalSubviews.Contains (dv.Target)) {
			//	throw new InvalidOperationException ($"View {dv.Target} is not a subview of {from}");
			//}
			if (dv.Target != this) {
				nEdges.Add ((dv.Target, from));
			}
			return;
		case Dim.DimCombine dc:
			CollectDim (dc._left,  from, ref nNodes, ref nEdges);
			CollectDim (dc._right, from, ref nNodes, ref nEdges);
			break;
		}
	}

	internal void CollectAll (View from, ref HashSet<View> nNodes, ref HashSet<(View, View)> nEdges)
	{
		// BUGBUG: This should really only work on initialized subviews
		foreach (var v in from.InternalSubviews /*.Where(v => v.IsInitialized)*/) {
			nNodes.Add (v);
			if (v.LayoutStyle != LayoutStyle.Computed) {
				continue;
			}
			CollectPos (v.X, v, ref nNodes, ref nEdges);
			CollectPos (v.Y, v, ref nNodes, ref nEdges);
			CollectDim (v.Width,  v, ref nNodes, ref nEdges);
			CollectDim (v.Height, v, ref nNodes, ref nEdges);
		}
	}

	// https://en.wikipedia.org/wiki/Topological_sorting
	internal static List<View> TopologicalSort (View superView, IEnumerable<View> nodes, ICollection<(View From, View To)> edges)
	{
		var result = new List<View> ();

		// Set of all nodes with no incoming edges
		var noEdgeNodes = new HashSet<View> (nodes.Where (n => edges.All (e => !e.To.Equals (n))));

		while (noEdgeNodes.Any ()) {
			//  remove a node n from S
			var n = noEdgeNodes.First ();
			noEdgeNodes.Remove (n);

			// add n to tail of L
			if (n != superView) {
				result.Add (n);
			}

			// for each node m with an edge e from n to m do
			foreach (var e in edges.Where (e => e.From.Equals (n)).ToArray ()) {
				var m = e.To;

				// remove edge e from the graph
				edges.Remove (e);

				// if m has no other incoming edges then
				if (edges.All (me => !me.To.Equals (m)) && m != superView) {
					// insert m into S
					noEdgeNodes.Add (m);
				}
			}
		}

		if (!edges.Any ()) {
			return result;
		}

		foreach ((var from, var to) in edges) {
			if (from == to) {
				// if not yet added to the result, add it and remove from edge
				if (result.Find (v => v == from) == null) {
					result.Add (from);
				}
				edges.Remove ((from, to));
			} else if (from.SuperView == to.SuperView) {
				// if 'from' is not yet added to the result, add it
				if (result.Find (v => v == from) == null) {
					result.Add (from);
				}
				// if 'to' is not yet added to the result, add it
				if (result.Find (v => v == to) == null) {
					result.Add (to);
				}
				// remove from edge
				edges.Remove ((from, to));
			} else if (from != superView?.GetTopSuperView (to, from) && !ReferenceEquals (from, to)) {
				if (ReferenceEquals (from.SuperView, to)) {
					throw new InvalidOperationException ($"ComputedLayout for \"{superView}\": \"{to}\" references a SubView (\"{from}\").");
				}
				throw new InvalidOperationException ($"ComputedLayout for \"{superView}\": \"{from}\" linked with \"{to}\" was not found. Did you forget to add it to {superView}?");
			}
		}
		// return L (a topologically sorted order)
		return result;
	} // TopologicalSort

	/// <summary>
	/// Overriden by <see cref="Frame"/> to do nothing, as the <see cref="Frame"/> does not have frames.
	/// </summary>
	internal virtual void LayoutFrames ()
	{
		if (Margin == null) {
			return; // CreateFrames() has not been called yet
		}

		if (Margin.Frame.Size != Frame.Size) {
			Margin._frame = new Rect (Point.Empty, Frame.Size);
			Margin.X = 0;
			Margin.Y = 0;
			Margin.Width = Frame.Size.Width;
			Margin.Height = Frame.Size.Height;
			Margin.SetNeedsLayout ();
			Margin.SetNeedsDisplay ();
		}

		var border = Margin.Thickness.GetInside (Margin.Frame);
		if (border != Border.Frame) {
			Border._frame = new Rect (new Point (border.Location.X, border.Location.Y), border.Size);
			Border.X = border.Location.X;
			Border.Y = border.Location.Y;
			Border.Width = border.Size.Width;
			Border.Height = border.Size.Height;
			Border.SetNeedsLayout ();
			Border.SetNeedsDisplay ();
		}

		var padding = Border.Thickness.GetInside (Border.Frame);
		if (padding != Padding.Frame) {
			Padding._frame = new Rect (new Point (padding.Location.X, padding.Location.Y), padding.Size);
			Padding.X = padding.Location.X;
			Padding.Y = padding.Location.Y;
			Padding.Width = padding.Size.Width;
			Padding.Height = padding.Size.Height;
			Padding.SetNeedsLayout ();
			Padding.SetNeedsDisplay ();
		}
	}

	/// <summary>
	/// Invoked when a view starts executing or when the dimensions of the view have changed, for example in
	/// response to the container view or terminal resizing.
	/// </summary>
	/// <remarks>
	///         <para>
	///         The position and dimensions of the view are indeterminate until the view has been initialized. Therefore,
	///         the behavior of this method is indeterminate if <see cref="IsInitialized"/> is <see langword="false"/>.
	///         </para>
	///         <para>
	///         Raises the <see cref="LayoutComplete"/> event) before it returns.
	///         </para>
	/// </remarks>
	public virtual void LayoutSubviews ()
	{
		if (!IsInitialized) {
			Debug.WriteLine ($"WARNING: LayoutSubviews called before view has been initialized. This is likely a bug in {this}");
		}

		if (!LayoutNeeded) {
			return;
		}

		LayoutFrames ();

		var oldBounds = Bounds;
		OnLayoutStarted (new LayoutEventArgs { OldBounds = oldBounds });

		SetTextFormatterSize ();

		// Sort out the dependencies of the X, Y, Width, Height properties
		var nodes = new HashSet<View> ();
		var edges = new HashSet<(View, View)> ();
		CollectAll (this, ref nodes, ref edges);
		var ordered = TopologicalSort (SuperView, nodes, edges);
		foreach (var v in ordered) {
			LayoutSubview (v, new Rect (GetBoundsOffset (), Bounds.Size));
		}

		// If the 'to' is rooted to 'from' and the layoutstyle is Computed it's a special-case.
		// Use LayoutSubview with the Frame of the 'from' 
		if (SuperView != null && GetTopSuperView () != null && LayoutNeeded && edges.Count > 0) {
			foreach ((var from, var to) in edges) {
				LayoutSubview (to, from.Frame);
			}
		}

		LayoutNeeded = false;

		OnLayoutComplete (new LayoutEventArgs { OldBounds = oldBounds });
	}

	void LayoutSubview (View v, Rect contentArea)
	{
		//if (v.LayoutStyle == LayoutStyle.Computed) {
		v.SetRelativeLayout (contentArea);
		//}

		v.LayoutSubviews ();
		v.LayoutNeeded = false;
	}

	bool ResizeView (bool autoSize)
	{
		if (!autoSize) {
			return false;
		}

		var boundsChanged = true;
		var newFrameSize = GetAutoSize ();
		if (IsInitialized && newFrameSize != Frame.Size) {
			if (ValidatePosDim) {
				// BUGBUG: This ain't right, obviously.  We need to figure out how to handle this.
				boundsChanged = ResizeBoundsToFit (newFrameSize);
			} else {
				Height = newFrameSize.Height;
				Width = newFrameSize.Width;
			}
		}
		return boundsChanged;
	}

	/// <summary>
	/// Resizes the View to fit the specified size. Factors in the HotKey.
	/// </summary>
	/// <param name="size"></param>
	/// <returns>whether the Bounds was changed or not</returns>
	bool ResizeBoundsToFit (Size size)
	{
		var boundsChanged = false;
		var canSizeW = TrySetWidth (size.Width - GetHotKeySpecifierLength (), out var rW);
		var canSizeH = TrySetHeight (size.Height - GetHotKeySpecifierLength (false), out var rH);
		if (canSizeW) {
			boundsChanged = true;
			_width = rW;
		}
		if (canSizeH) {
			boundsChanged = true;
			_height = rH;
		}
		if (boundsChanged) {
			Bounds = new Rect (Bounds.X, Bounds.Y, canSizeW ? rW : Bounds.Width, canSizeH ? rH : Bounds.Height);
		}

		return boundsChanged;
	}


	/// <summary>
	/// Determines if the View's <see cref="Width"/> can be set to a new value.
	/// </summary>
	/// <param name="desiredWidth"></param>
	/// <param name="resultWidth">
	/// Contains the width that would result if <see cref="Width"/> were set to
	/// <paramref name="desiredWidth"/>"/>
	/// </param>
	/// <returns>
	/// <see langword="true"/> if the View's <see cref="Width"/> can be changed to the specified value. False
	/// otherwise.
	/// </returns>
	internal bool TrySetWidth (int desiredWidth, out int resultWidth)
	{
		var w = desiredWidth;
		bool canSetWidth;
		switch (Width) {
		case Dim.DimCombine _:
		case Dim.DimView _:
		case Dim.DimFill _:
			// It's a Dim.DimCombine and so can't be assigned. Let it have it's Width anchored.
			w = Width.Anchor (w);
			canSetWidth = !ValidatePosDim;
			break;
		case Dim.DimFactor factor:
			// Tries to get the SuperView Width otherwise the view Width.
			var sw = SuperView != null ? SuperView.Frame.Width : w;
			if (factor.IsFromRemaining ()) {
				sw -= Frame.X;
			}
			w = Width.Anchor (sw);
			canSetWidth = !ValidatePosDim;
			break;
		default:
			canSetWidth = true;
			break;
		}
		resultWidth = w;

		return canSetWidth;
	}

	/// <summary>
	/// Determines if the View's <see cref="Height"/> can be set to a new value.
	/// </summary>
	/// <param name="desiredHeight"></param>
	/// <param name="resultHeight">
	/// Contains the width that would result if <see cref="Height"/> were set to
	/// <paramref name="desiredHeight"/>"/>
	/// </param>
	/// <returns>
	/// <see langword="true"/> if the View's <see cref="Height"/> can be changed to the specified value. False
	/// otherwise.
	/// </returns>
	internal bool TrySetHeight (int desiredHeight, out int resultHeight)
	{
		var h = desiredHeight;
		bool canSetHeight;
		switch (Height) {
		case Dim.DimCombine _:
		case Dim.DimView _:
		case Dim.DimFill _:
			// It's a Dim.DimCombine and so can't be assigned. Let it have it's height anchored.
			h = Height.Anchor (h);
			canSetHeight = !ValidatePosDim;
			break;
		case Dim.DimFactor factor:
			// Tries to get the SuperView height otherwise the view height.
			var sh = SuperView != null ? SuperView.Frame.Height : h;
			if (factor.IsFromRemaining ()) {
				sh -= Frame.Y;
			}
			h = Height.Anchor (sh);
			canSetHeight = !ValidatePosDim;
			break;
		default:
			canSetHeight = true;
			break;
		}
		resultHeight = h;

		return canSetHeight;
	}

	/// <summary>
	/// Finds which view that belong to the <paramref name="start"/> superview at the provided location.
	/// </summary>
	/// <param name="start">The superview where to look for.</param>
	/// <param name="x">The column location in the superview.</param>
	/// <param name="y">The row location in the superview.</param>
	/// <param name="resx">The found view screen relative column location.</param>
	/// <param name="resy">The found view screen relative row location.</param>
	/// <returns>
	/// The view that was found at the <praramref name="x"/> and <praramref name="y"/> coordinates.
	/// <see langword="null"/> if no view was found.
	/// </returns>
	public static View FindDeepestView (View start, int x, int y, out int resx, out int resy)
	{
		resy = resx = 0;
		if (start == null || !start.Frame.Contains (x, y)) {
			return null;
		}

		var startFrame = start.Frame;
		if (start.InternalSubviews != null) {
			var count = start.InternalSubviews.Count;
			if (count > 0) {
				var boundsOffset = start.GetBoundsOffset ();
				var rx = x - (startFrame.X + boundsOffset.X);
				var ry = y - (startFrame.Y + boundsOffset.Y);
				for (var i = count - 1; i >= 0; i--) {
					var v = start.InternalSubviews [i];
					if (v.Visible && v.Frame.Contains (rx, ry)) {
						var deep = FindDeepestView (v, rx, ry, out resx, out resy);
						if (deep == null) {
							return v;
						}
						return deep;
					}
				}
			}
		}
		resx = x - startFrame.X;
		resy = y - startFrame.Y;
		return start;
	}
}