using UnityEngine;
using UnityEditor;
using System;
using System.Reflection;

public class TestScaleGUI : EditorWindow
{
    private MethodInfo _getTopRect = null;
    private PropertyInfo _getVisibleRect = null;
    private MethodInfo _setTransform = null;
    private Vector2 _scrPos = Vector2.zero;

    //Windowメニュー
    [MenuItem( "Test/TestScaleGUI" )]
    public static void Create()
    {
        var win = GetWindow<TestScaleGUI>( "TestScaleGUI" );
    }

    private void OnEnable()
    {
        Assembly UnityEngine = System.Reflection.Assembly.Load( "UnityEngine.dll" );
        Type GUIClipType = UnityEngine.GetType( "UnityEngine.GUIClip" );
        _getTopRect = GUIClipType.GetMethod( "GetTopRect", BindingFlags.Static | BindingFlags.NonPublic );
        _getVisibleRect = GUIClipType.GetProperty( "visibleRect", BindingFlags.Static | BindingFlags.Public );
        _setTransform = GUIClipType.GetMethod( "SetTransform", BindingFlags.Static | BindingFlags.NonPublic );
    }

    private void OnDisable()
    {
    }

    private Rect GUIClipGetTopRect()
    {
        if( _getTopRect == null )
            return new Rect( 0, 0, position.width, position.height );
        var rect = (Rect)_getTopRect.Invoke( null, null );
        return rect;
    }

    private Rect GUIClipGetVisibleRect()
    {
        if( _getVisibleRect == null )
            return new Rect( 0, 0, position.width, position.height );
        var rect = (Rect)_getVisibleRect.GetValue( null, null );
        return rect;
    }

    private void GUIClipSetTransform( Matrix4x4 clipTransform, Matrix4x4 objectTransform, Rect clipRect )
    {
        if( _setTransform == null )
            return;
        _setTransform.Invoke( null, new object[]{ clipTransform, objectTransform, clipRect } );
    }

    private void OnGUI()
    {
        var topRect = GUIClipGetTopRect();

        var pivotPoint = Vector2.zero;
        var rect = new Rect( 0, 0, topRect.width, topRect.height );

        var zoom = 2.0f; // 1.0f～ 値が大きいほど、小さく表示される
        var invZoom = 1.0f / zoom;

        {
            using( var scrollScope = new EditorGUILayout.ScrollViewScope( _scrPos ) )
            {
                _scrPos = scrollScope.scrollPosition;

                var area = GUILayoutUtility.GetRect( new GUIContent( string.Empty ), GUIStyle.none, GUILayout.Width( 3000 ), GUILayout.Height( 3000 ) );
                {
                    GUIUtility.ScaleAroundPivot( Vector2.one * invZoom, pivotPoint );
                    var visibleRect = GUIClipGetVisibleRect();
                    visibleRect.position *= zoom;
                    visibleRect.size *= zoom;
                    GUIClipSetTransform( Matrix4x4.identity, Matrix4x4.identity, visibleRect );

                    //内部のGUI　適当！
                    int x, y;
                    x = 3000 -25;
                    for( y = 0; y <= 6000; y+= 100 )
                        GUI.Button( new Rect( x, y, 50, 50 ), y.ToString() );

                    x = 6000 -25;
                    for( y = 0; y <= 6000; y+= 100 )
                        GUI.Button( new Rect( x, y, 50, 50 ), y.ToString() );

                    y = 3000 - 25;
                    for( x = -25; x <= 6000; x+= 100 )
                        GUI.Button( new Rect( x, y, 50, 50 ), x.ToString() );

                    y = 6000 - 25;
                    for( x = 0; x <= 6000; x+= 100 )
                        GUI.Button( new Rect( x, y, 50, 50 ), x.ToString() );


                    GUI.matrix = Matrix4x4.identity;
                }
            }
        }
    }
}