DockUtilities.cs

using System.Collections;
using System.Collections.Generic;
using System.Reflection;
using UnityEditor;
using UnityEngine;

public static class DockUtilities
{
	public enum DockPosition
	{
		Left,
		Top,
		Right,
		Bottom
	}

	private static Vector2 GetFakeMousePosition(EditorWindow wnd, DockPosition position)
	{
		Vector2 mousePosition = Vector2.zero;

		// The 20 is required to make the docking work.
		// Smaller values might not work when faking the mouse position.
		switch (position)
		{
			case DockPosition.Left: mousePosition = new Vector2(20, wnd.position.size.y / 2); break;
			case DockPosition.Top: mousePosition = new Vector2(wnd.position.size.x / 2, 20); break;
			case DockPosition.Right: mousePosition = new Vector2(wnd.position.size.x - 20, wnd.position.size.y / 2); break;
			case DockPosition.Bottom: mousePosition = new Vector2(wnd.position.size.x / 2, wnd.position.size.y - 20); break;
		}

		return new Vector2(wnd.position.x + mousePosition.x, wnd.position.y + mousePosition.y);
	}

	/// <summary>
	/// Docks the "docked" window to the "anchor" window at the given position
	/// </summary>
	public static void DockWindow(this EditorWindow anchor, EditorWindow docked, DockPosition position)
	{
		var anchorParent = GetParentOf(anchor);

		SetDragSource(anchorParent, GetParentOf(docked));
		PerformDrop(GetWindowOf(anchorParent), docked, GetFakeMousePosition(anchor, position));
	}

	static object GetParentOf(object target)
	{
		var field = target.GetType().GetField("m_Parent", BindingFlags.Instance | BindingFlags.NonPublic);
		return field.GetValue(target);
	}

	static object GetWindowOf(object target)
	{
		var property = target.GetType().GetProperty("window", BindingFlags.Instance | BindingFlags.Public);
		return property.GetValue(target, null);
	}

	static void SetDragSource(object target, object source)
	{
		var field = target.GetType().GetField("s_OriginalDragSource", BindingFlags.Static | BindingFlags.NonPublic);
		field.SetValue(null, source);
	}

	static void PerformDrop(object window, EditorWindow child, Vector2 screenPoint)
	{
		var rootSplitViewProperty = window.GetType().GetProperty("rootSplitView", BindingFlags.Instance | BindingFlags.Public);
		object rootSplitView = rootSplitViewProperty.GetValue(window, null);

		var dragMethod = rootSplitView.GetType().GetMethod("DragOver", BindingFlags.Instance | BindingFlags.Public);
		var dropMethod = rootSplitView.GetType().GetMethod("PerformDrop", BindingFlags.Instance | BindingFlags.Public);

		var dropInfo = dragMethod.Invoke(rootSplitView, new object[] { child, screenPoint });
		dropMethod.Invoke(rootSplitView, new object[] { child, dropInfo, screenPoint });
	}
}