Creating & editing BoxColliders intuitively in Unity

BoxColliderWizard.cs

#if UNITY_EDITOR
using System.Collections.Generic;
using System.Reflection;
using UnityEditor;
using UnityEditor.IMGUI.Controls;
using UnityEngine.Rendering;
#endif
using UnityEngine;

public class BoxColliderWizard : MonoBehaviour
{
#if UNITY_EDITOR
	[ContextMenu( "Help" )]
	private void ShowHelp()
	{
		EditorUtility.DisplayDialog( "Help",
			"In Edit mode, you can edit the active child colliders using Move, Rotate, Scale and Rect tools. " +
			"These colliders need to have 0,0,0 Center and 1,1,1 Size values.\n\n" +
			"The following shortcuts work while Scene view has focus:\n" +
			"- Tab: toggle active mode\n" +
			"- Z: toggle Pivot Position\n" +
			"- X: toggle Collider Alignment (in Create mode)", "OK" );
	}
#endif
}

#if UNITY_EDITOR
[CustomEditor( typeof( BoxColliderWizard ) )]
[CanEditMultipleObjects]
public class BoxColliderWizardEditor : Editor
{
	private enum Mode { None, Create, Edit, Delete };
	private enum VolumeDrawMode { None, BaseOnly, VolumeOutline, VolumeFilled };
	private enum PivotPosition { Surface, Center };
	private enum CreationStage { PendingClick, SetLength, SetWidth, SetHeight };
	private enum ColliderAlignment { XZ, XY, YZ, RaycastDetermines };

	private class ColliderHolder
	{
		public readonly Collider collider;
		public readonly Transform colliderTransform;

		// Values used in Rect Tool
		public Vector3 snapshotPosition;
		public Quaternion snapshotRotation;
		public Vector3 snapshotScale;

		public bool isActiveCollider, isBeingCreated;
		public double lastActiveTime;

		public Vector3 position
		{
			get { return colliderTransform.position; }
			set
			{
				if( !isBeingCreated )
					Undo.RecordObject( colliderTransform, "Modify Collider" );

				colliderTransform.position = value;
			}
		}

		public Quaternion rotation
		{
			get { return colliderTransform.rotation; }
			set
			{
				if( !isBeingCreated )
					Undo.RecordObject( colliderTransform, "Modify Collider" );

				colliderTransform.rotation = value;
			}
		}

		public Vector3 scale
		{
			get { return colliderTransform.lossyScale; }
			set
			{
				if( !isBeingCreated )
					Undo.RecordObject( colliderTransform, "Modify Collider" );

				Transform parent = colliderTransform.parent;
				int siblingIndex = colliderTransform.GetSiblingIndex();
				colliderTransform.SetParent( null, true );
				try
				{
					colliderTransform.localScale = new Vector3( Mathf.Abs( value.x ), Mathf.Abs( value.y ), Mathf.Abs( value.z ) );
				}
				finally
				{
					colliderTransform.SetParent( parent, true );
					colliderTransform.SetSiblingIndex( siblingIndex );
				}
			}
		}

		public Vector3 surfacePosition
		{
			get { return ( pivotPosition == PivotPosition.Center ) ? colliderTransform.position : ( colliderTransform.position - colliderTransform.rotation * new Vector3( 0f, colliderTransform.lossyScale.y * 0.5f, 0f ) ); }
			set
			{
				if( !isBeingCreated )
					Undo.RecordObject( colliderTransform, "Modify Collider" );

				colliderTransform.position = ( pivotPosition == PivotPosition.Center ) ? value : ( value + colliderTransform.rotation * new Vector3( 0f, colliderTransform.lossyScale.y * 0.5f, 0f ) );
			}
		}

		public ColliderHolder( Collider collider )
		{
			this.collider = collider;
			colliderTransform = collider.transform;
		}

		public void TakeSnapshot()
		{
			snapshotPosition = colliderTransform.position;
			snapshotRotation = colliderTransform.rotation;
			snapshotScale = colliderTransform.lossyScale;

			if( pivotPosition == PivotPosition.Surface )
				snapshotPosition -= snapshotRotation * new Vector3( 0f, snapshotScale.y * 0.5f, 0f );

			isActiveCollider = false;
		}

		public bool SurfaceRaycast( Ray ray, out float enter )
		{
			Vector3 surfacePosition = this.surfacePosition;
			Plane plane = new Plane( rotation * Vector3.up, surfacePosition );
			if( !plane.Raycast( ray, out enter ) )
				return false;

			Vector3 hitLocalPoint = Matrix4x4.TRS( surfacePosition, rotation, new Vector3( scale.x, 1f, scale.z ) ).inverse.MultiplyPoint3x4( ray.GetPoint( enter ) );
			return Mathf.Abs( hitLocalPoint.x ) <= 0.5f && Mathf.Abs( hitLocalPoint.z ) <= 0.5f;
		}

		public void GetSurfaceWorldCorners( Vector3[] fillArray )
		{
			Vector3 position = colliderTransform.position;
			Quaternion rotation = colliderTransform.rotation;
			Vector3 scale = colliderTransform.lossyScale;

			if( pivotPosition == PivotPosition.Surface )
				position -= rotation * new Vector3( 0f, scale.y * 0.5f, 0f );

			Vector3 tangent = rotation * new Vector3( 0f, 0f, scale.z * 0.5f );
			Vector3 bitangent = rotation * new Vector3( scale.x * 0.5f, 0f, 0f );

			fillArray[0] = position - tangent - bitangent; // Rear left
			fillArray[1] = position + tangent - bitangent; // Forward left
			fillArray[2] = position + tangent + bitangent; // Forward right
			fillArray[3] = position - tangent + bitangent; // Rear right
		}
	}

	private readonly Color COLLIDER_FILL_COLOR = new Color( 0f, 1f, 0f, 0.3f );
	private readonly Color COLLIDER_FILL_COLOR_DELETE = new Color( 1f, 0f, 0f, 0.3f );
	private readonly Color COLLIDER_OUTLINE_COLOR = new Color( 1f, 1f, 1f, 1f );
	private readonly Color COLLIDER_CREATION_GRIDLINES_COLOR = new Color( 1f, 1f, 1f, 0.85f );
	private readonly Color COLLIDER_CREATION_GRIDLINES_OBSTRUCTED_COLOR = new Color( 0.5f, 0.5f, 0.5f, 0.85f );
	private readonly Color COLLIDER_CREATION_REFERENCE_PLANE_COLOR = new Color( 0f, 0f, 1f, 0.3f );
	private readonly Color COLLIDER_CREATION_REFERENCE_PLANE_OBSTRUCTED_COLOR = new Color( 1f, 0f, 0f, 0.3f );

	#region Saved Properties
	private Mode? m_mode;
	private Mode mode
	{
		get { if( !m_mode.HasValue ) m_mode = (Mode) EditorPrefs.GetInt( "BCWMode", (int) Mode.None ); return m_mode.Value; }
		set
		{
			if( mode != value )
			{
				m_mode = value;
				Tools.hidden = ( value != Mode.None );

				EditorApplication.update -= SceneView.RepaintAll;
				if( value == Mode.Delete )
					EditorApplication.update += SceneView.RepaintAll;

				if( colliderCreationStage != CreationStage.PendingClick )
				{
					colliderCreationStage = CreationStage.PendingClick;
					DestroyUnfinishedCollider();
				}

				EditorPrefs.SetInt( "BCWMode", (int) value );
			}
		}
	}

	private VolumeDrawMode? m_volumeDrawMode;
	private VolumeDrawMode volumeDrawMode
	{
		get { if( !m_volumeDrawMode.HasValue ) m_volumeDrawMode = (VolumeDrawMode) EditorPrefs.GetInt( "BCWVolume", (int) VolumeDrawMode.VolumeOutline ); return m_volumeDrawMode.Value; }
		set
		{
			if( volumeDrawMode != value )
			{
				m_volumeDrawMode = value;
				EditorPrefs.SetInt( "BCWVolume", (int) value );
			}
		}
	}

	private static PivotPosition? m_pivotPosition;
	private static PivotPosition pivotPosition
	{
		get { if( !m_pivotPosition.HasValue ) m_pivotPosition = (PivotPosition) EditorPrefs.GetInt( "BCWPivot", (int) PivotPosition.Surface ); return m_pivotPosition.Value; }
		set
		{
			if( pivotPosition != value )
			{
				m_pivotPosition = value;
				EditorPrefs.SetInt( "BCWPivot", (int) value );
			}
		}
	}

	private ColliderAlignment? m_colliderCreationAlignment;
	private ColliderAlignment colliderCreationAlignment
	{
		get { if( !m_colliderCreationAlignment.HasValue ) m_colliderCreationAlignment = (ColliderAlignment) EditorPrefs.GetInt( "BCWCAlignment", (int) ColliderAlignment.XZ ); return m_colliderCreationAlignment.Value; }
		set
		{
			if( colliderCreationAlignment != value )
			{
				m_colliderCreationAlignment = value;
				EditorPrefs.SetInt( "BCWCAlignment", (int) value );
			}
		}
	}

	private bool? m_showColliderProperties;
	private bool showColliderProperties
	{
		get { if( !m_showColliderProperties.HasValue ) m_showColliderProperties = EditorPrefs.GetBool( "BCWShowProp", true ); return m_showColliderProperties.Value; }
		set
		{
			if( showColliderProperties != value )
			{
				m_showColliderProperties = value;
				EditorPrefs.SetBool( "BCWShowProp", value );
			}
		}
	}
	#endregion

	private BoxColliderWizard mainWizard;

	private readonly List<ColliderHolder> colliders = new List<ColliderHolder>( 64 );
	private readonly List<ColliderHolder> visibleColliders = new List<ColliderHolder>( 64 );

	private Material fillMaterial, outlineMaterial;

	private bool isPointerDown, isRightMouseButtonDown, isRightClick;
	private Vector3 previousHandlePosition;
	private bool? colliderGizmosWereActive;

	private CreationStage colliderCreationStage = CreationStage.PendingClick;
	private Vector3? colliderCreationReferencePlaneCenter;
	private Vector3 colliderCreationPreviousPoint, colliderCreationClickedPoint;
	private Quaternion colliderCreationOrientation;

	private double rightClickTime;
	private Vector2 rightClickPosition;

#if UNITY_2017_1_OR_NEWER
	private readonly BoxBoundsHandle boundsHandle = new BoxBoundsHandle();
#else
	private readonly BoxBoundsHandle boundsHandle = new BoxBoundsHandle( 1453541 );
#endif

#if UNITY_2017_3_OR_NEWER
	private readonly Plane[] sceneCameraFrustumPlanes = new Plane[6];
#endif

	private readonly string[] modeLabels = new string[4] { "None", "Create", "Edit", "Delete" };

	private readonly Vector3[] colliderSurfaceWorldCorners = new Vector3[4];
	private readonly object[] resizeHandleParameters = new object[4];
	private readonly object[] otherHandleParameters = new object[3];

	private readonly Quaternion[] refAlignments = new Quaternion[]
	{
		Quaternion.LookRotation( Vector3.right, Vector3.up ),
		Quaternion.LookRotation( Vector3.right, Vector3.forward ),
		Quaternion.LookRotation( Vector3.up, Vector3.forward ),
		Quaternion.LookRotation( Vector3.up, Vector3.right ),
		Quaternion.LookRotation( Vector3.forward, Vector3.right ),
		Quaternion.LookRotation( Vector3.forward, Vector3.up )
	};

	#region Reflection Variables
	private readonly MethodInfo moveHandlesGUI = typeof( EditorWindow ).Assembly.GetType( "UnityEditor.RectTool" ).GetMethod( "MoveHandlesGUI", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static );
#pragma warning disable 0414 // Will be needed if Rect tool's rotate handles are uncommented
	private readonly MethodInfo rotationHandlesGUI = typeof( EditorWindow ).Assembly.GetType( "UnityEditor.RectTool" ).GetMethod( "RotationHandlesGUI", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static );
#pragma warning restore 0414
	private readonly MethodInfo resizeHandlesGUI = typeof( EditorWindow ).Assembly.GetType( "UnityEditor.RectTool" ).GetMethod( "ResizeHandlesGUI", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static );
	private readonly MethodInfo raycastWorld = typeof( EditorWindow ).Assembly.GetType( "UnityEditor.SceneViewMotion" ).GetMethod( "RaycastWorld", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static );

	private readonly FieldInfo s_Moving = typeof( EditorWindow ).Assembly.GetType( "UnityEditor.RectTool" ).GetField( "s_Moving", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static );
	private readonly PropertyInfo minDragDifference = typeof( EditorWindow ).Assembly.GetType( "UnityEditor.ManipulationToolUtility" ).GetProperty( "minDragDifference", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static );
#if UNITY_2020_1_OR_NEWER
	private readonly PropertyInfo incrementalSnapActive = typeof( EditorWindow ).Assembly.GetType( "UnityEditor.EditorSnapSettings" ).GetProperty( "incrementalSnapActive", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static );
	private readonly PropertyInfo gridSnapActive = typeof( EditorWindow ).Assembly.GetType( "UnityEditor.EditorSnapSettings" ).GetProperty( "gridSnapActive", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static );
	private readonly PropertyInfo vertexSnapActive = typeof( EditorWindow ).Assembly.GetType( "UnityEditor.EditorSnapSettings" ).GetProperty( "vertexSnapActive", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Static );
#endif
	#endregion

	private void OnEnable()
	{
		mainWizard = (BoxColliderWizard) target;

		InitializeColliders();

		fillMaterial = new Material( Shader.Find( "Hidden/Internal-Colored" ) ) { hideFlags = HideFlags.HideAndDontSave };
		fillMaterial.SetInt( "_SrcBlend", (int) BlendMode.SrcAlpha );
		fillMaterial.SetInt( "_DstBlend", (int) BlendMode.OneMinusSrcAlpha );
		fillMaterial.SetInt( "_Cull", (int) CullMode.Off );
		fillMaterial.SetInt( "_ZWrite", (int) CompareFunction.Disabled );
		fillMaterial.SetFloat( "_ZBias", -1f );

		outlineMaterial = new Material( Shader.Find( "Hidden/Internal-Colored" ) ) { hideFlags = HideFlags.HideAndDontSave };
		outlineMaterial.SetInt( "_SrcBlend", (int) BlendMode.SrcAlpha );
		outlineMaterial.SetInt( "_DstBlend", (int) BlendMode.OneMinusSrcAlpha );
		outlineMaterial.SetInt( "_Cull", (int) CullMode.Off );
		outlineMaterial.SetInt( "_ZTest", (int) CompareFunction.Always );

		Tools.hidden = ( mode != Mode.None );

		if( mode == Mode.Delete )
		{
			EditorApplication.update -= SceneView.RepaintAll;
			EditorApplication.update += SceneView.RepaintAll;
		}

		// Undo&redo might delete/restore a collider we are editing, refresh the colliders list to be safe
		Undo.undoRedoPerformed -= InitializeColliders;
		Undo.undoRedoPerformed += InitializeColliders;

#if !UNITY_2018_4_OR_NEWER
		// Unity doesn't call OnDisable automatically before code compilation on Unity 5.6 but it does on 2018.4.
		// I don't know which intermediate versions call OnDisable automatically, so me manually call OnDisable on
		// versions up to 2018.4 just before code compilation
		EditorApplication.update -= CallOnDisableBeforeCompilation;
		EditorApplication.update += CallOnDisableBeforeCompilation;
#endif
#if !UNITY_2019_4_OR_NEWER
		// On older Unity versions, editing or creating colliders while the wizard isn't uniformly scaled causes the
		// collider's scale to skyrocket. Thus, we won't activate the wizard on those versions until it is uniformly scaled
		EditorApplication.update -= ShowErrorWhenWizardIsSkewed;
		EditorApplication.update += ShowErrorWhenWizardIsSkewed;
#endif
	}

	private void OnDisable()
	{
		Tools.hidden = false;

		EditorApplication.update -= SceneView.RepaintAll;
		Undo.undoRedoPerformed -= InitializeColliders;
#if !UNITY_2018_4_OR_NEWER
		EditorApplication.update -= CallOnDisableBeforeCompilation;
#endif
#if !UNITY_2019_4_OR_NEWER
		EditorApplication.update -= ShowErrorWhenWizardIsSkewed;
#endif

		// Restore BoxCollider gizmos state
		if( colliderGizmosWereActive.HasValue )
		{
			ColliderHolder existingBoxCollider = colliders.Find( ( collider ) => collider.collider );
			if( existingBoxCollider != null )
				UnityEditorInternal.InternalEditorUtility.SetIsInspectorExpanded( existingBoxCollider.collider, colliderGizmosWereActive.Value );
			else
			{
				// Use a dummy BoxCollider to toggle gizmos
				BoxCollider dummyCollider = new GameObject().AddComponent<BoxCollider>();
				try
				{
					UnityEditorInternal.InternalEditorUtility.SetIsInspectorExpanded( dummyCollider, colliderGizmosWereActive.Value );
				}
				finally
				{
					DestroyImmediate( dummyCollider.gameObject );
				}
			}

			colliderGizmosWereActive = null;
		}

		if( colliderCreationStage != CreationStage.PendingClick )
		{
			colliderCreationStage = CreationStage.PendingClick;
			DestroyUnfinishedCollider();
		}

		if( fillMaterial )
		{
			DestroyImmediate( fillMaterial );
			fillMaterial = null;
		}

		if( outlineMaterial )
		{
			DestroyImmediate( outlineMaterial );
			outlineMaterial = null;
		}
	}

	private void InitializeColliders()
	{
		if( colliderCreationStage != CreationStage.PendingClick )
		{
			colliderCreationStage = CreationStage.PendingClick;
			DestroyUnfinishedCollider();
		}

		colliders.Clear();

		foreach( Object target in targets )
		{
			BoxColliderWizard wizard = (BoxColliderWizard) target;
			foreach( BoxCollider boxCollider in wizard.GetComponentsInChildren<BoxCollider>( false ) )
			{
				if( boxCollider && boxCollider.transform != wizard.transform && boxCollider.center == Vector3.zero && boxCollider.size == Vector3.one )
				{
					colliders.Add( new ColliderHolder( boxCollider ) );

					if( !colliderGizmosWereActive.HasValue )
					{
						// Hide BoxCollider gizmos
						colliderGizmosWereActive = UnityEditorInternal.InternalEditorUtility.GetIsInspectorExpanded( boxCollider );
						UnityEditorInternal.InternalEditorUtility.SetIsInspectorExpanded( boxCollider, false );
					}
				}
			}
		}

		if( !colliderGizmosWereActive.HasValue )
		{
			// Use a dummy BoxCollider to toggle gizmos
			BoxCollider dummyCollider = new GameObject().AddComponent<BoxCollider>();
			try
			{
				colliderGizmosWereActive = UnityEditorInternal.InternalEditorUtility.GetIsInspectorExpanded( dummyCollider );
				UnityEditorInternal.InternalEditorUtility.SetIsInspectorExpanded( dummyCollider, false );
			}
			finally
			{
				DestroyImmediate( dummyCollider.gameObject );
			}
		}
	}

	private void DestroyUnfinishedCollider()
	{
		ColliderHolder colliderToCreate = colliders.Find( ( collider ) => collider.isBeingCreated );
		if( colliderToCreate != null )
		{
			colliders.Remove( colliderToCreate );
			DestroyImmediate( colliderToCreate.collider.gameObject );
		}
	}

#if !UNITY_2018_4_OR_NEWER
	private void CallOnDisableBeforeCompilation()
	{
		if( EditorApplication.isCompiling )
			OnDisable();
	}
#endif

#if !UNITY_2019_4_OR_NEWER
	private void ShowErrorWhenWizardIsSkewed()
	{
		// Check if the wizard is skewed (not uniformly-scaled). When it is skewed, SceneView shows error message at cursor position
		// and we want to constantly repaint Scene view to keep this error message's position correct
		Vector3 wizardScale = mainWizard.transform.lossyScale;
		if( !Mathf.Approximately( wizardScale.x, wizardScale.y ) || !Mathf.Approximately( wizardScale.x, wizardScale.z ) )
			SceneView.RepaintAll();
	}
#endif

	public override void OnInspectorGUI()
	{
		EditorGUI.BeginChangeCheck();

		mode = (Mode) GUILayout.Toolbar( (int) mode, modeLabels );

		EditorGUILayout.Space();

		volumeDrawMode = (VolumeDrawMode) EditorGUILayout.EnumPopup( "Draw Volume", volumeDrawMode );
		pivotPosition = (PivotPosition) EditorGUILayout.EnumPopup( "Pivot Position (Z)", pivotPosition );

		if( mode == Mode.Create )
		{
			GUI.enabled = colliderCreationStage == CreationStage.PendingClick || colliderCreationStage == CreationStage.SetLength;
			colliderCreationAlignment = (ColliderAlignment) EditorGUILayout.EnumPopup( "Collider Alignment (X)", colliderCreationAlignment );

			if( colliderCreationReferencePlaneCenter.HasValue )
				EditorGUILayout.HelpBox( "Creating colliders on a reference plane (world geometry is ignored as long as reference plane is hit). Right click to disable the reference plane", MessageType.Info );
			else
				EditorGUILayout.HelpBox( "To create colliders on a reference plane that is centered at a specified point, hold CTRL+Shift and left click the target position", MessageType.None );

			if( colliderCreationStage != CreationStage.PendingClick )
			{
				ColliderHolder colliderToCreate = colliders.Find( ( collider ) => collider.isBeingCreated );
				if( colliderToCreate != null )
				{
					GUI.enabled = false;

					EditorGUILayout.Space();
					DrawColliderProperties( colliderToCreate );
				}
			}

			GUI.enabled = true;
		}
		else if( colliders.Count > 0 )
		{
			EditorGUILayout.Space();

#if UNITY_2019_1_OR_NEWER
			showColliderProperties = EditorGUILayout.BeginFoldoutHeaderGroup( showColliderProperties, "Colliders" );
#else
			showColliderProperties = EditorGUILayout.Foldout( showColliderProperties, "Colliders", true );
#endif

			if( showColliderProperties )
			{
				foreach( ColliderHolder collider in colliders )
				{
					DrawColliderProperties( collider );
					EditorGUILayout.Space();
				}
			}

#if UNITY_2019_1_OR_NEWER
			EditorGUILayout.EndFoldoutHeaderGroup();
#endif
		}

		if( EditorGUI.EndChangeCheck() )
			SceneView.RepaintAll();
	}

	private void DrawColliderProperties( ColliderHolder collider )
	{
		GUILayout.Box( collider.collider.name, GUILayout.ExpandWidth( true ) );

		bool wideMode = EditorGUIUtility.wideMode;
		float labelWidth = EditorGUIUtility.labelWidth;
		EditorGUIUtility.wideMode = true;
		EditorGUIUtility.labelWidth = 60f;

		EditorGUI.BeginChangeCheck();

		EditorGUI.BeginChangeCheck();
		Vector3 position = EditorGUILayout.Vector3Field( "Position", collider.colliderTransform.localPosition );
		if( EditorGUI.EndChangeCheck() )
		{
			if( !collider.isBeingCreated )
				Undo.RecordObject( collider.colliderTransform, "Modify Collider" );

			collider.colliderTransform.localPosition = position;
		}

		EditorGUI.BeginChangeCheck();
		Vector3 rotation = EditorGUILayout.Vector3Field( "Rotation", collider.colliderTransform.localEulerAngles );
		if( EditorGUI.EndChangeCheck() )
		{
			if( !collider.isBeingCreated )
				Undo.RecordObject( collider.colliderTransform, "Modify Collider" );

			collider.colliderTransform.localEulerAngles = rotation;
		}

		EditorGUI.BeginChangeCheck();
		Vector3 scale = EditorGUILayout.Vector3Field( "Scale", collider.colliderTransform.localScale );
		if( EditorGUI.EndChangeCheck() )
		{
			if( !collider.isBeingCreated )
				Undo.RecordObject( collider.colliderTransform, "Modify Collider" );

			collider.colliderTransform.localScale = scale;
		}

		if( EditorGUI.EndChangeCheck() )
			SceneView.RepaintAll();

		EditorGUIUtility.labelWidth = labelWidth;
		EditorGUIUtility.wideMode = wideMode;
	}

	private void OnSceneGUI()
	{
		// Draw scene GUI only once, not per selected BoxColliderWizard
		if( target != mainWizard )
			return;

		if( volumeDrawMode == VolumeDrawMode.None )
			return;

#if !UNITY_2018_4_OR_NEWER
		// OnDisable is called manually just before code recompilation, we can't call OnSceneGUI until compilation is completed
		if( !fillMaterial || !outlineMaterial )
			return;
#endif

		Event ev = Event.current;

		HandleSceneGUIInput( ev );

		ColliderHolder activeCollider = colliders.Find( ( collider ) => collider.isActiveCollider );
		ColliderHolder colliderToCreate = colliders.Find( ( collider ) => collider.isBeingCreated );
		ColliderHolder colliderToDelete = null;
		if( mode == Mode.Delete )
		{
			Ray ray = HandleUtility.GUIPointToWorldRay( ev.mousePosition );
			float closestColliderDistance = float.PositiveInfinity;
			foreach( ColliderHolder collider in colliders )
			{
				RaycastHit hit;
				if( collider.collider.Raycast( ray, out hit, float.PositiveInfinity ) && hit.distance < closestColliderDistance )
				{
					closestColliderDistance = hit.distance;
					colliderToDelete = collider;
				}
			}
		}

		// Find colliders that are visible to Scene view camera
#if UNITY_2017_3_OR_NEWER
		GeometryUtility.CalculateFrustumPlanes( SceneView.currentDrawingSceneView.camera, sceneCameraFrustumPlanes );
#else
		Plane[] sceneCameraFrustumPlanes = GeometryUtility.CalculateFrustumPlanes( SceneView.currentDrawingSceneView.camera );
#endif
		visibleColliders.Clear();
		foreach( ColliderHolder collider in colliders )
		{
			Vector3 scale = collider.scale;
			float maxScaleComponent = scale.x;
			if( scale.y > maxScaleComponent )
				maxScaleComponent = scale.y;
			if( scale.z > maxScaleComponent )
				maxScaleComponent = scale.z;

			if( GeometryUtility.TestPlanesAABB( sceneCameraFrustumPlanes, new Bounds( collider.position, new Vector3( maxScaleComponent, maxScaleComponent, maxScaleComponent ) ) ) )
				visibleColliders.Add( collider );
		}

		// Frame to the collider when F key is pressed
		if( ( mode == Mode.Create || mode == Mode.Edit ) && ev.type == EventType.KeyDown && ev.keyCode == KeyCode.F )
		{
			ColliderHolder colliderToFocus = colliderToCreate ?? activeCollider;
			if( colliderToFocus != null )
			{
#if UNITY_2018_2_OR_NEWER
				SceneView.currentDrawingSceneView.Frame( colliderToFocus.collider.bounds, false );
#else
				float boundsSize = colliderToFocus.collider.bounds.extents.magnitude * 3.3f;
				if( boundsSize != Mathf.Infinity )
				{
					if( boundsSize == 0f )
						boundsSize = 10f;

					SceneView sceneView = SceneView.currentDrawingSceneView;
					EditorApplication.delayCall += () => sceneView.LookAt( colliderToFocus.collider.bounds.center, sceneView.rotation, boundsSize * 2.2f, sceneView.orthographic, true );
				}
#endif
				ev.Use();
			}
		}

		if( ev.type == EventType.Repaint )
			DrawColliderVisuals( colliderToDelete, ev );

		bool isPanningWindow = ( ev.alt && !isPointerDown );
		if( volumeDrawMode != VolumeDrawMode.BaseOnly )
			DrawColliderBounds( visibleColliders, !isPanningWindow && Tools.current == Tool.Rect && mode == Mode.Edit );
		else if( colliderToCreate != null ) // Always draw the created collider's Bounds
			DrawColliderBounds( new ColliderHolder[1] { colliderToCreate }, false );

#if !UNITY_2019_4_OR_NEWER
		if( mode != Mode.None )
		{
			// This plugin doesn't work well with skewed colliders on old Unity versions, so don't run the plugin at all if this is the case
			Vector3 wizardScale = mainWizard.transform.lossyScale;
			if( !Mathf.Approximately( wizardScale.x, wizardScale.y ) || !Mathf.Approximately( wizardScale.x, wizardScale.z ) )
			{
				// Show error message at cursor position
				Handles.BeginGUI();
				Vector2 cursorPos = HandleUtility.GUIPointToScreenPixelCoordinate( ev.mousePosition );
				cursorPos.y = Screen.height - cursorPos.y;
				EditorGUI.HelpBox( new Rect( cursorPos - new Vector2( 100f, 90f ), new Vector2( 200f, 45f ) ), "BoxColliderWizard doesn't work when the wizard's Transform isn't uniformly scaled (skewed).", MessageType.Error );
				Handles.EndGUI();

				return;
			}
		}
#endif

		if( mode == Mode.None || isPanningWindow )
			return;

		switch( mode )
		{
			case Mode.Create:
			{
				EditorGUI.BeginChangeCheck();
				HandleCreateMode( ref colliderToCreate, ev );
				if( EditorGUI.EndChangeCheck() )
					Repaint();

				break;
			}
			case Mode.Edit:
			{
				EditorGUI.BeginChangeCheck();
				HandleEditMode( ref activeCollider, ev );
				if( EditorGUI.EndChangeCheck() )
					Repaint();

				break;
			}
			case Mode.Delete:
			{
				HandleDeleteMode( ref colliderToDelete, ev );
				break;
			}
		}

		if( activeCollider != null )
		{
			activeCollider.lastActiveTime = EditorApplication.timeSinceStartup;
			activeCollider.isActiveCollider = true;
		}

		HandleUtility.AddDefaultControl( 0 );
	}

	private void HandleSceneGUIInput( Event ev )
	{
		isRightClick = false;

		if( ev.type == EventType.MouseDown )
		{
			if( ev.button == 0 && !ev.alt ) // Left click
			{
				foreach( ColliderHolder collider in colliders )
					collider.TakeSnapshot();

				isPointerDown = true;
			}
			else if( ev.button == 1 ) // Right click
			{
				isRightMouseButtonDown = true;

				if( !ev.alt )
				{
					rightClickTime = EditorApplication.timeSinceStartup;
					rightClickPosition = ev.mousePosition;
				}
			}
		}
		else if( ev.type == EventType.MouseUp )
		{
			if( ev.button == 0 ) // Left release
			{
				isPointerDown = false;

				// RectTool's moveHandlesGUI function changes selection on mouse click (i.e. when mouse doesn't move after press: 's_Moving == false'). We don't want that
				// Source: https://github.com/Unity-Technologies/UnityCsReference/blob/61f92bd79ae862c4465d35270f9d1d57befd1761/Editor/Mono/GUI/Tools/BuiltinTools.cs#L889-L890
				if( mode == Mode.Edit )
					s_Moving.SetValue( null, true );
			}
			else if( ev.button == 1 ) // Right release
			{
				isRightMouseButtonDown = false;

				if( EditorApplication.timeSinceStartup - rightClickTime <= 0.3f && Vector2.Distance( ev.mousePosition, rightClickPosition ) <= 5f )
					isRightClick = true;
			}
		}
		else if( ev.type == EventType.KeyDown && !ev.control && !ev.command )
		{
			if( ev.keyCode == KeyCode.Tab && !ev.alt ) // Toggle mode
			{
				mode = (Mode) ( (int) mode + ( ev.shift ? -1 : 1 ) );
				if( (int) mode >= 4 )
					mode = (Mode) 0;
				else if( (int) mode < 0 )
					mode = (Mode) 3;

				Repaint();
				ev.Use();
			}
			else if( ev.character == '\t' && !ev.alt )
			{
				// Unity sends (keyCode == KeyCode.Tab) event and (character == '\t') event separately (but consecutively).
				// If we don't eat both of them, upon clicking Tab, Scene View's search field gains focus. We need to change
				// 'mode' in only one of them because we want to switch one tab per Tab click, not two
				ev.Use();
			}
			else if( ev.keyCode == KeyCode.Z ) // Toggle pivotPosition
			{
				pivotPosition = (PivotPosition) ( ( (int) pivotPosition + 1 ) % 2 );

				Repaint();
				ev.Use();
			}
			else if( ev.keyCode == KeyCode.X && mode == Mode.Create ) // Toggle colliderCreationAlignment
			{
				colliderCreationAlignment = (ColliderAlignment) ( ( (int) colliderCreationAlignment + 1 ) % 4 );

				Repaint();
				ev.Use();
			}
		}
	}

	private void DrawColliderVisuals( ColliderHolder colliderToDelete, Event ev )
	{
		Matrix4x4 handlesMatrix = Handles.matrix;
		Color handlesColor = Handles.color;

		if( volumeDrawMode == VolumeDrawMode.BaseOnly || pivotPosition == PivotPosition.Center )
		{
			// Draw all outlines first so that they can be obstructed by VolumeFilled
			outlineMaterial.SetPass( 0 );
			foreach( ColliderHolder collider in visibleColliders )
			{
				collider.GetSurfaceWorldCorners( colliderSurfaceWorldCorners );

				GL.Begin( GL.LINES );
				GL.Color( COLLIDER_OUTLINE_COLOR );
				for( int i = 0; i < 4; i++ )
				{
					GL.Vertex( colliderSurfaceWorldCorners[i] );
					GL.Vertex( colliderSurfaceWorldCorners[( i + 1 ) % 4] );
				}
				GL.End();
			}
		}

		if( volumeDrawMode != VolumeDrawMode.VolumeFilled && mode != Mode.Delete )
		{
			// Draw surface only
			fillMaterial.SetPass( 0 );
			foreach( ColliderHolder collider in visibleColliders )
			{
				collider.GetSurfaceWorldCorners( colliderSurfaceWorldCorners );

				GL.Begin( GL.TRIANGLES );
				GL.Color( COLLIDER_FILL_COLOR );
				for( int i = 0; i < 2; i++ )
				{
					GL.Vertex( colliderSurfaceWorldCorners[i * 2 + 0] );
					GL.Vertex( colliderSurfaceWorldCorners[i * 2 + 1] );
					GL.Vertex( colliderSurfaceWorldCorners[( i * 2 + 2 ) % 4] );
				}
				GL.End();
			}
		}
		else
		{
			// Draw whole volume
			Color volumeFillColor = new Color( COLLIDER_FILL_COLOR.r, COLLIDER_FILL_COLOR.g, COLLIDER_FILL_COLOR.b, COLLIDER_FILL_COLOR.a * 0.5f );
			bool handlesLighting = Handles.lighting;
			CompareFunction zTest = Handles.zTest;
			Handles.zTest = CompareFunction.LessEqual;
			Handles.lighting = false;

			foreach( ColliderHolder collider in visibleColliders )
			{
				Handles.color = ( collider != colliderToDelete ) ? volumeFillColor : COLLIDER_FILL_COLOR_DELETE;
				Handles.matrix = Matrix4x4.TRS( collider.position, collider.rotation, collider.scale );
				Handles.CubeHandleCap( 0, Vector3.zero, Quaternion.identity, 1f, ev.type );
			}

			Handles.lighting = handlesLighting;
			Handles.zTest = zTest;
			Handles.color = handlesColor;
			Handles.matrix = handlesMatrix;
		}
	}

	private void DrawColliderBounds( IList<ColliderHolder> colliders, bool interactable )
	{
		Matrix4x4 handlesMatrix = Handles.matrix;

		// Don't allow interacting with the bounds handles if Rect tool isn't selected
		bool guiEnabled = GUI.enabled;
		GUI.enabled = interactable;
#if UNITY_2018_1_OR_NEWER
		boundsHandle.midpointHandleSizeFunction = interactable ? BoxBoundsHandle.DefaultMidpointHandleSizeFunction : (Handles.SizeFunction) null;
#else
		boundsHandle.midpointHandleSizeFunction = ( position ) => ( interactable ? HandleUtility.GetHandleSize( position ) * 0.03f : 0f );
#endif
		EditorGUI.BeginChangeCheck();

		foreach( ColliderHolder collider in colliders )
		{
			Matrix4x4 matrix = Matrix4x4.TRS( Vector3.zero, collider.rotation, Vector3.one );
			Handles.matrix = matrix;

			boundsHandle.center = matrix.inverse.MultiplyPoint3x4( collider.position );
			boundsHandle.size = collider.scale;

			EditorGUI.BeginChangeCheck();
			boundsHandle.DrawHandle();
			if( EditorGUI.EndChangeCheck() && interactable )
			{
				collider.position = matrix.MultiplyPoint3x4( boundsHandle.center );
				collider.scale = boundsHandle.size;
			}
		}

		if( EditorGUI.EndChangeCheck() && interactable )
			Repaint();

		GUI.enabled = guiEnabled;
		Handles.matrix = handlesMatrix;
	}

	private void HandleCreateMode( ref ColliderHolder colliderToCreate, Event ev )
	{
		// RMB is clicked or ESC is pressed
		if( isRightClick || ( ev.isKey && ev.keyCode == KeyCode.Escape ) )
		{
			if( colliderToCreate != null )
			{
				// Cancel created collider
				DestroyUnfinishedCollider();
				colliderToCreate = null;
				colliderCreationStage = CreationStage.PendingClick;

				if( !isRightClick ) // Don't eat right click event because it might be controlling Scene view 'zoom' or 'look around' gizmos
					ev.Use();

				return;
			}
			else if( colliderCreationStage == CreationStage.PendingClick && colliderCreationReferencePlaneCenter.HasValue )
			{
				// Disable reference plane
				colliderCreationReferencePlaneCenter = null;

				if( !isRightClick )
					ev.Use();

				Repaint();
			}
		}

		if( ev.alt )
			return;

		switch( colliderCreationStage )
		{
			case CreationStage.PendingClick:
			{
				Quaternion orientation;
				switch( colliderCreationAlignment )
				{
					case ColliderAlignment.XZ: orientation = Quaternion.identity; break;
					case ColliderAlignment.XY: orientation = Quaternion.Euler( -90f, 0f, 0f ); break;
					case ColliderAlignment.YZ: orientation = Quaternion.Euler( -90f, 90f, 0f ); break;
					default: orientation = colliderCreationOrientation; break;
				}

				if( ev.isMouse )
				{
					bool referencePlaneHit = false;
					if( colliderCreationReferencePlaneCenter.HasValue )
					{
						// Raycast against it reference plane
						Ray ray = HandleUtility.GUIPointToWorldRay( ev.mousePosition );
						float enter;
						if( new Plane( orientation * Vector3.up, colliderCreationReferencePlaneCenter.Value ).Raycast( ray, out enter ) )
						{
							colliderCreationPreviousPoint = ray.GetPoint( enter );
							colliderCreationOrientation = orientation;

							referencePlaneHit = true;
						}
					}

					// Raycast against world geometry
					// Normally, we would want to call it inside 'if( !referencePlaneHit )' but somehow, this function causes
					// the Scene view to constantly repaint which is awesome! Calling SceneView.RepaintAll inside EditorApplication.update
					// also repaints the Scene view constantly but it uses more CPU than this method. Probably, this method invokes repaint
					// less often or omits some redundant events that SceneView.RepaintAll doesn't
					object[] parameters = new object[2] { ev.mousePosition, null };
					bool worldRaycastHit = (bool) raycastWorld.Invoke( null, parameters );

					if( !referencePlaneHit )
					{
						if( worldRaycastHit )
						{
							RaycastHit hit = (RaycastHit) parameters[1];

							colliderCreationPreviousPoint = hit.point;
							colliderCreationOrientation = Quaternion.FromToRotation( Vector3.up, hit.normal );
						}
						else
						{
							// No geometry found, use a dummy point specified distance away from the camera
							colliderCreationPreviousPoint = HandleUtility.GUIPointToWorldRay( ev.mousePosition ).GetPoint( 10f );
							colliderCreationOrientation = Quaternion.identity;
						}
					}
				}

				// Draw reference plane at cursor position if RMB isn't held
				if( !isRightMouseButtonDown && colliderCreationReferencePlaneCenter.HasValue )
				{
					const float REFERENCE_PLANE_SIZE = 3f;

					Vector3 corner1 = colliderCreationPreviousPoint + orientation * new Vector3( -REFERENCE_PLANE_SIZE, 0f, -REFERENCE_PLANE_SIZE );
					Vector3 corner2 = colliderCreationPreviousPoint + orientation * new Vector3( -REFERENCE_PLANE_SIZE, 0f, REFERENCE_PLANE_SIZE );
					Vector3 corner3 = colliderCreationPreviousPoint + orientation * new Vector3( REFERENCE_PLANE_SIZE, 0f, REFERENCE_PLANE_SIZE );
					Vector3 corner4 = colliderCreationPreviousPoint + orientation * new Vector3( REFERENCE_PLANE_SIZE, 0f, -REFERENCE_PLANE_SIZE );

					fillMaterial.SetInt( "_ZTest", (int) CompareFunction.Greater );
					fillMaterial.SetPass( 0 );
					GL.Begin( GL.TRIANGLES );
					GL.Color( COLLIDER_CREATION_REFERENCE_PLANE_OBSTRUCTED_COLOR );
					GL.Vertex( corner1 );
					GL.Vertex( corner2 );
					GL.Vertex( corner3 );
					GL.Vertex( corner3 );
					GL.Vertex( corner4 );
					GL.Vertex( corner1 );
					GL.End();

					fillMaterial.SetInt( "_ZTest", (int) CompareFunction.LessEqual );
					fillMaterial.SetPass( 0 );
					GL.Begin( GL.TRIANGLES );
					GL.Color( COLLIDER_CREATION_REFERENCE_PLANE_COLOR );
					GL.Vertex( corner1 );
					GL.Vertex( corner2 );
					GL.Vertex( corner3 );
					GL.Vertex( corner3 );
					GL.Vertex( corner4 );
					GL.Vertex( corner1 );
					GL.End();
				}

				// Draw the hovered point's XYZ axes
				float handleSize = HandleUtility.GetHandleSize( colliderCreationPreviousPoint );
				Color handlesColor = Handles.color;
				Handles.color = Color.blue;
				Handles.ArrowHandleCap( 0, colliderCreationPreviousPoint, orientation, handleSize, ev.type );
				Handles.color = Color.red;
				Handles.ArrowHandleCap( 0, colliderCreationPreviousPoint, orientation * Quaternion.Euler( 0f, 90f, 0f ), handleSize, ev.type );
				Handles.color = Color.green;
				Handles.ArrowHandleCap( 0, colliderCreationPreviousPoint, orientation * Quaternion.Euler( -90f, 0f, 0f ), handleSize, ev.type );
				if( ev.control && ev.shift && !colliderCreationReferencePlaneCenter.HasValue )
				{
					// Draw a small sphere at cursor indicating that we are in 'enable reference plane' mode
					CompareFunction zTest = Handles.zTest;
					Handles.zTest = CompareFunction.LessEqual;
					Handles.color = new Color( 1f, 1f, 0f, 0.5f );
					Handles.SphereHandleCap( 0, colliderCreationPreviousPoint, Quaternion.identity, handleSize * 0.2f, ev.type );
					Handles.zTest = zTest;
				}
				Handles.color = handlesColor;

				if( ev.type == EventType.MouseDown && ev.button == 0 )
				{
					if( ev.control && ev.shift && !colliderCreationReferencePlaneCenter.HasValue )
					{
						// Enable reference plane when both CTRL and Shift are held
						colliderCreationReferencePlaneCenter = colliderCreationPreviousPoint;

						ev.Use();
						Repaint();
					}
					else
					{
						BoxCollider boxCollider = new GameObject( "BoxCollider", typeof( BoxCollider ) ).GetComponent<BoxCollider>();
						boxCollider.center = Vector3.zero;
						boxCollider.size = Vector3.one;
						boxCollider.transform.SetParent( mainWizard.transform, false );
						boxCollider.transform.SetPositionAndRotation( colliderCreationPreviousPoint, orientation );
						boxCollider.transform.localScale = Vector3.zero;

						colliderToCreate = new ColliderHolder( boxCollider ) { isBeingCreated = true };
						colliders.Add( colliderToCreate );

						colliderCreationClickedPoint = colliderCreationPreviousPoint;
						colliderCreationStage = CreationStage.SetLength;

						ev.Use();
					}
				}

				break;
			}
			case CreationStage.SetLength:
			{
				const float MIN_COLLIDER_LENGTH = 0.001f;

				Vector3 upDirection, forwardDirection, rightDirection;
				switch( colliderCreationAlignment )
				{
					case ColliderAlignment.XZ: upDirection = Vector3.up; forwardDirection = Vector3.forward; rightDirection = Vector3.right; break;
					case ColliderAlignment.XY: upDirection = Vector3.back; forwardDirection = Vector3.up; rightDirection = Vector3.right; break;
					case ColliderAlignment.YZ: upDirection = Vector3.left; forwardDirection = Vector3.up; rightDirection = Vector3.back; break;
					default: upDirection = colliderCreationOrientation * Vector3.up; forwardDirection = colliderCreationOrientation * Vector3.forward; rightDirection = colliderCreationOrientation * Vector3.right; break;
				}

				// Draw gridlines on the alignment plane
				float gridlinesSpacing = HandleUtility.GetHandleSize( colliderCreationPreviousPoint );
				DrawGridlines( colliderCreationPreviousPoint, forwardDirection, rightDirection, 4, gridlinesSpacing, COLLIDER_CREATION_GRIDLINES_COLOR );
				fillMaterial.SetInt( "_ZTest", (int) CompareFunction.Greater );
				DrawGridlines( colliderCreationPreviousPoint, forwardDirection, rightDirection, 4, gridlinesSpacing, COLLIDER_CREATION_GRIDLINES_OBSTRUCTED_COLOR );
				fillMaterial.SetInt( "_ZTest", (int) CompareFunction.LessEqual );

				Ray ray = HandleUtility.GUIPointToWorldRay( ev.mousePosition );
				Plane plane = new Plane( upDirection, colliderCreationClickedPoint );
				float enter;
				if( plane.Raycast( ray, out enter ) )
				{
					Vector3 hitPoint = ray.GetPoint( enter );
					Vector3 lengthDirection = hitPoint - colliderCreationPreviousPoint;
					if( ev.shift )
					{
						// Snap direction to an axis
						Vector3 longestProjection = Vector3.Project( lengthDirection, rightDirection );
						for( int i = 0; i < 3; i++ )
						{
							Vector3 projection = Vector3.Project( lengthDirection, forwardDirection + ( i - 1 ) * rightDirection );
							if( projection.sqrMagnitude > longestProjection.sqrMagnitude )
								longestProjection = projection;
						}

						lengthDirection = longestProjection;
					}

					if( lengthDirection.magnitude >= MIN_COLLIDER_LENGTH )
					{
						colliderToCreate.position = ev.control ? colliderCreationPreviousPoint : ( colliderCreationPreviousPoint + lengthDirection * 0.5f );
						colliderToCreate.rotation = Quaternion.LookRotation( lengthDirection, upDirection );
						colliderToCreate.scale = new Vector3( 0f, 0f, ev.control ? ( lengthDirection.magnitude * 2f ) : lengthDirection.magnitude );
					}
				}

				if( ev.type == EventType.MouseDown && ev.button == 0 )
				{
					if( colliderToCreate.scale.magnitude < MIN_COLLIDER_LENGTH )
					{
						DestroyUnfinishedCollider();
						colliderToCreate = null;
						colliderCreationStage = CreationStage.PendingClick;
					}
					else
					{
						colliderCreationPreviousPoint = colliderToCreate.position;
						colliderCreationClickedPoint = plane.Raycast( ray, out enter ) ? ray.GetPoint( enter ) : colliderCreationPreviousPoint;
						colliderCreationStage = CreationStage.SetWidth;
					}

					ev.Use();
				}

				break;
			}
			case CreationStage.SetWidth:
			{
				Ray ray = HandleUtility.GUIPointToWorldRay( ev.mousePosition );
				Plane plane = new Plane( colliderToCreate.colliderTransform.up, colliderCreationClickedPoint );
				float enter;
				if( plane.Raycast( ray, out enter ) )
				{
					Vector3 hitPoint = ray.GetPoint( enter );
					Vector3 widthDirection = Vector3.Project( hitPoint - colliderCreationClickedPoint, colliderToCreate.colliderTransform.right );
					colliderToCreate.position = ev.control ? colliderCreationPreviousPoint : ( colliderCreationPreviousPoint + widthDirection * 0.5f );

					Vector3 scale = colliderToCreate.scale;
					scale.x = ev.control ? ( widthDirection.magnitude * 2f ) : widthDirection.magnitude;
					colliderToCreate.scale = scale;
				}

				if( ev.type == EventType.MouseDown && ev.button == 0 && !ev.alt )
				{
					colliderCreationPreviousPoint = colliderToCreate.position;
					colliderCreationClickedPoint = plane.Raycast( ray, out enter ) ? ray.GetPoint( enter ) : colliderCreationPreviousPoint;
					colliderCreationStage = CreationStage.SetHeight;

					ev.Use();
				}

				break;
			}
			case CreationStage.SetHeight:
			{
				// While setting height, plane normal should preferably point towards scene view camera's forward direction
				Vector3 cameraForward = colliderToCreate.colliderTransform.InverseTransformDirection( SceneView.currentDrawingSceneView.camera.transform.forward );
				cameraForward.y = 0f;
				cameraForward = colliderToCreate.colliderTransform.TransformDirection( cameraForward );

				Vector3 planeNormal;
				if( cameraForward.sqrMagnitude > 0.00001f )
					planeNormal = cameraForward;
				else if( !SceneView.currentDrawingSceneView.orthographic )
					planeNormal = colliderToCreate.colliderTransform.forward;
				else
				{
					// In orthographic projection, while looking at the collider directly from above, we can't use a plane normal that is
					// perpendicular to camera because otherwise collider's Transform values skyrocket in an instant! We should use a
					// non-perpendicular plane normal. Ideally, collider size should increase when we move the mouse up or right whereas
					// it should decrease when we move the mouse down or left
					planeNormal = colliderToCreate.colliderTransform.up + SceneView.currentDrawingSceneView.camera.transform.TransformDirection( new Vector3( -0.707f, -0.707f, 0f ) ); // 0.707f: 1/sqrt(2)
				}

				Ray ray = HandleUtility.GUIPointToWorldRay( ev.mousePosition );
				Plane plane = new Plane( planeNormal, colliderCreationClickedPoint );
				float enter;
				if( plane.Raycast( ray, out enter ) )
				{
					Vector3 hitPoint = ray.GetPoint( enter );
					Vector3 heightDirection = Vector3.Project( hitPoint - colliderCreationClickedPoint, colliderToCreate.colliderTransform.up );
					colliderToCreate.position = ev.control ? colliderCreationPreviousPoint : ( colliderCreationPreviousPoint + heightDirection * 0.5f );

					Vector3 scale = colliderToCreate.scale;
					scale.y = ev.control ? ( heightDirection.magnitude * 2f ) : heightDirection.magnitude;
					colliderToCreate.scale = scale;
				}

				if( ev.type == EventType.MouseDown && ev.button == 0 )
				{
					colliderCreationStage = CreationStage.PendingClick;

					Undo.RegisterCreatedObjectUndo( colliderToCreate.collider.gameObject, "Create Collider" );
					colliderToCreate.isBeingCreated = false;
					colliderToCreate.isActiveCollider = true;
					colliderToCreate = null;

					ev.Use();
				}

				break;
			}
		}
	}

	private void HandleEditMode( ref ColliderHolder activeCollider, Event ev )
	{
		switch( Tools.current )
		{
			case Tool.Move:
			{
				foreach( ColliderHolder collider in visibleColliders )
				{
					EditorGUI.BeginChangeCheck();
					Vector3 position = Handles.PositionHandle( collider.surfacePosition, ( Tools.pivotRotation == PivotRotation.Local ) ? collider.rotation : Quaternion.identity );
					if( EditorGUI.EndChangeCheck() )
					{
						activeCollider = collider;
						collider.surfacePosition = position;
					}
				}

				break;
			}
			case Tool.Rotate:
			{
				foreach( ColliderHolder collider in visibleColliders )
				{
					EditorGUI.BeginChangeCheck();
					Quaternion rotation = Handles.RotationHandle( collider.rotation, collider.surfacePosition );
					if( EditorGUI.EndChangeCheck() )
					{
						activeCollider = collider;

						// If we unparent the collider first, it almost never skews during rotation
						Undo.RecordObject( collider.colliderTransform, "Modify Collider" );
						Transform parent = collider.colliderTransform.parent;
						int siblingIndex = collider.colliderTransform.GetSiblingIndex();
						collider.colliderTransform.SetParent( null, true );
						try
						{
							if( pivotPosition == PivotPosition.Center )
								collider.rotation = rotation;
							else
							{
								// Rotate from the surface
								Quaternion delta = rotation * Quaternion.Inverse( collider.rotation );
								float angle;
								Vector3 axis;
								delta.ToAngleAxis( out angle, out axis );
								collider.colliderTransform.RotateAround( collider.surfacePosition, axis, angle );
							}
						}
						finally
						{
							collider.colliderTransform.SetParent( parent, true );
							collider.colliderTransform.SetSiblingIndex( siblingIndex );
						}
					}
				}

				break;
			}

			case Tool.Scale:
			{
				foreach( ColliderHolder collider in visibleColliders )
				{
					Vector3 surfacePosition = collider.surfacePosition;
					Vector3 initialScale = collider.scale;

					EditorGUI.BeginChangeCheck();
					Vector3 scale = Handles.ScaleHandle( initialScale, surfacePosition, collider.rotation, HandleUtility.GetHandleSize( surfacePosition ) );
					if( EditorGUI.EndChangeCheck() )
					{
						activeCollider = collider;

#if UNITY_2019_1_OR_NEWER && !UNITY_2020_2_OR_NEWER // Scaling in all axes is broken on some versions: https://issuetracker.unity3d.com/issues/object-size-is-doubled-when-center-scaling-it-with-custom-script-using-handles-dot-scalehandle-method
						int changedScaleComponents = 0;
						if( initialScale.x != scale.x )
							changedScaleComponents++;
						if( initialScale.y != scale.y )
							changedScaleComponents++;
						if( initialScale.z != scale.z )
							changedScaleComponents++;

						if( changedScaleComponents == 1 )
#endif
						{
							if( pivotPosition == PivotPosition.Center )
								collider.scale = scale;
							else
							{
								// Scale from the surface. The most reliable way to do it is to use a dummy pivot GameObject
								Undo.RecordObject( collider.colliderTransform, "Modify Collider" );
								Transform pivot = new GameObject().transform;
								try
								{
									pivot.SetPositionAndRotation( surfacePosition, collider.rotation );
									pivot.localScale = collider.scale;

									Transform parent = collider.colliderTransform.parent;
									int siblingIndex = collider.colliderTransform.GetSiblingIndex();
									collider.colliderTransform.SetParent( pivot, true );
									try
									{
										pivot.localScale = scale;
									}
									finally
									{
										collider.colliderTransform.SetParent( parent, true );
										collider.colliderTransform.SetSiblingIndex( siblingIndex );
									}
								}
								finally
								{
									DestroyImmediate( pivot.gameObject );
								}
							}
						}
					}
				}

				break;
			}
			case Tool.Rect:
			{
				// Credit: https://github.com/Unity-Technologies/UnityCsReference/blob/61f92bd79ae862c4465d35270f9d1d57befd1761/Editor/Mono/GUI/Tools/BuiltinTools.cs#L514-L574
				// Credit: https://github.com/Unity-Technologies/UnityCsReference/blob/61f92bd79ae862c4465d35270f9d1d57befd1761/Editor/Mono/GUI/Tools/TransformManipulator.cs
				Color handlesColor = Handles.color;
				int controlID = GUIUtility.hotControl;
				bool isPaintEvent = ( !isPointerDown || ev.type == EventType.Repaint );

				// Rect resize handle
				foreach( ColliderHolder collider in visibleColliders )
				{
					EditorGUI.BeginChangeCheck();
					object[] parameters = GetParametersForRectToolHandles( collider, true, isPaintEvent );
					Vector3 scale = (Vector3) resizeHandlesGUI.Invoke( null, parameters );
					if( EditorGUI.EndChangeCheck() && isPointerDown && ( activeCollider == null || activeCollider == collider ) )
					{
						Quaternion rectRotation = (Quaternion) parameters[2];
						Vector3 scalePivot = (Vector3) parameters[3];
						SetScaleDelta( collider, scale, scalePivot, rectRotation );
					}

					if( GUIUtility.hotControl != controlID && activeCollider == null )
						activeCollider = collider;
				}

				// Rect rotate handle
				//foreach( ColliderHolder collider in visibleColliders )
				//{
				//	EditorGUI.BeginChangeCheck();
				//	object[] parameters = GetParametersForRectToolHandles( collider, false, isPaintEvent );
				//	Quaternion rotation = (Quaternion) rotationHandlesGUI.Invoke( null, parameters );
				//	if( EditorGUI.EndChangeCheck() && isPointerDown && ( activeCollider == null || activeCollider == collider ) )
				//	{
				//		// I have no idea what's going on here
				//		Quaternion rectRotation = (Quaternion) parameters[2];
				//		Quaternion delta = Quaternion.Inverse( rectRotation ) * rotation;
				//		delta.ToAngleAxis( out float angle, out Vector3 axis );
				//		axis = rectRotation * axis;

				//		collider.rotation *= Quaternion.Inverse( collider.snapshotRotation ) * Quaternion.AngleAxis( angle, axis ) * collider.snapshotRotation;
				//		collider.rotation = collider.rotation.normalized; // Without this, rotation eventually fails
				//	}

				//	if( GUIUtility.hotControl != controlID && activeCollider == null )
				//		activeCollider = collider;
				//}

				if( ev.type == EventType.MouseDown && activeCollider == null )
				{
					// Neither resize handle nor rotate handle has captured the input; only move handle is left
					// Move handle should pick the collider that is closest to the camera. So we raycast against
					// all colliders and consider the closest one the active collider. If two colliders are at the
					// same distance, set the collider that was most recently interacted active
					Ray ray = HandleUtility.GUIPointToWorldRay( ev.mousePosition );
					float minDistance = float.PositiveInfinity;
					foreach( ColliderHolder collider in visibleColliders )
					{
						float enter;
						if( collider.SurfaceRaycast( ray, out enter ) )
						{
							if( Mathf.Approximately( minDistance, enter ) )
							{
								if( collider.lastActiveTime > activeCollider.lastActiveTime )
								{
									activeCollider = collider;
									minDistance = enter;
								}
							}
							else if( enter < minDistance )
							{
								activeCollider = collider;
								minDistance = enter;
							}
						}
					}
				}

				// Rect move handle
				foreach( ColliderHolder collider in visibleColliders )
				{
					if( activeCollider == collider )
					{
						EditorGUI.BeginChangeCheck();
						Vector3 newPos = (Vector3) moveHandlesGUI.Invoke( null, GetParametersForRectToolHandles( collider, false, isPaintEvent ) );
						if( EditorGUI.EndChangeCheck() && isPointerDown && ( activeCollider == null || activeCollider == collider ) && newPos != previousHandlePosition )
						{
							previousHandlePosition = newPos;
							SetPositionDelta( collider, newPos - collider.snapshotPosition );
						}
					}
				}

				// moveHandlesGUI modifies Handles.color and doesn't automatically reset it
				Handles.color = handlesColor;

				break;
			}
		}
	}

	private void HandleDeleteMode( ref ColliderHolder colliderToDelete, Event ev )
	{
		if( colliderToDelete != null && ev.type == EventType.MouseDown && ev.button == 0 )
		{
			Undo.DestroyObjectImmediate( colliderToDelete.collider.gameObject );
			colliders.Remove( colliderToDelete );
			colliderToDelete = null;

			ev.Use();
			GUIUtility.ExitGUI();
		}
	}

	private void DrawGridlines( Vector3 center, Vector3 verticalDir, Vector3 horizontalDir, int gridlineCount, float spacing, Color color )
	{
		// We have a number of ways to draw gridlines:
		// - Using outlineMaterial with GL.LINES: This is the easiest solution. Gridlines will always be visible on screen.
		//   The downside is, parts of it that are occluded by scene geometry may not be easily noticeable since they will
		//   share the same color with the parts that aren't occluded by scene geometry
		// - Using fillMaterial in one step with GL.LINES: Parts of the gridlines that are occluded by scene geometry won't be
		//   visible in Scene view but seeing these parts (with a different color than the unoccluded parts) would give more
		//   information to the user. Another downside is that, GL.LINES doesn't support _ZBias so it has major z-fighting issues
		// - Using fillMaterial in two steps with GL.LINES: In the second step, we can draw occluded parts with a different color
		//   which is awesome. Still, we have the terrible z-fighting issue
		// - Using fillMaterial in two steps with GL.QUADS: Unlike GL.LINES, GL.QUADS do support _ZBias so it doesn't have z-fighting
		//   issues. However, when looked at a steep angle, they can look very thin. To avoid this, we need to adjust their thickness
		//   vectors while looking from steep angles. But no matter how hard I've tried, I couldn't find a good solution for it, so I
		//   gave up on adjusting the thickness vectors
		// 
		// Currently, I'm using the latest method since I do want to draw occluded parts with separate color but I don't want z-fighting.

		float length = spacing * gridlineCount;
		Vector3 startPos = center + verticalDir * length * 0.5f - horizontalDir * length * 0.5f;

		// GL.LINES approach
		//fillMaterial.SetPass( 0 );
		//GL.Begin( GL.LINES );
		//GL.Color( color );
		//for( int i = 0; i < gridlineCount; i++ )
		//{
		//	Vector3 gridPosition = startPos - verticalDir * ( i + 0.5f ) * spacing;
		//	GL.Vertex( gridPosition );
		//	GL.Vertex( gridPosition + horizontalDir * length );

		//	gridPosition = startPos + horizontalDir * ( i + 0.5f ) * spacing;
		//	GL.Vertex( gridPosition );
		//	GL.Vertex( gridPosition - verticalDir * length );
		//}
		//GL.End();

		// GL.QUADS approach
		float steepness = Mathf.LerpUnclamped( 0.025f, 0.01f, Mathf.Pow( Mathf.Abs( Vector3.Dot( ( SceneView.currentDrawingSceneView.camera.transform.position - center ).normalized, Vector3.Cross( horizontalDir, verticalDir ) ) ), 0.6f ) );
		Vector3 thicknessHorizontalDir = horizontalDir * spacing * steepness;
		Vector3 thicknessVerticalDir = verticalDir * spacing * steepness;

		fillMaterial.SetPass( 0 );
		GL.Begin( GL.QUADS );
		GL.Color( color );
		for( int i = 0; i < gridlineCount; i++ )
		{
			Vector3 gridPosition = startPos - verticalDir * ( i + 0.5f ) * spacing;
			GL.Vertex( gridPosition - thicknessVerticalDir );
			GL.Vertex( gridPosition + thicknessVerticalDir );
			GL.Vertex( gridPosition + horizontalDir * length + thicknessVerticalDir );
			GL.Vertex( gridPosition + horizontalDir * length - thicknessVerticalDir );

			gridPosition = startPos + horizontalDir * ( i + 0.5f ) * spacing;
			GL.Vertex( gridPosition - thicknessHorizontalDir );
			GL.Vertex( gridPosition + thicknessHorizontalDir );
			GL.Vertex( gridPosition - verticalDir * length + thicknessHorizontalDir );
			GL.Vertex( gridPosition - verticalDir * length - thicknessHorizontalDir );
		}
		GL.End();
	}

	#region Rect Tool Helper Functions
	private object[] GetParametersForRectToolHandles( ColliderHolder collider, bool isResizeHandle, bool isPaintEvent )
	{
		object[] result = isResizeHandle ? resizeHandleParameters : otherHandleParameters;

		Vector3 scale = collider.scale;
		Vector2 colliderSize = new Vector2( scale.x, scale.z );
		result[0] = new Rect( colliderSize * -0.5f, colliderSize ); // Rect
		result[1] = isPaintEvent ? collider.surfacePosition : collider.snapshotPosition; // Handle position
		result[2] = collider.rotation * Quaternion.Euler( 90f, 0f, 0f ); // Rect rotation

		return result;
	}

	// Credit: https://github.com/Unity-Technologies/UnityCsReference/blob/61f92bd79ae862c4465d35270f9d1d57befd1761/Editor/Mono/GUI/Tools/TransformManipulator.cs#L89-L141
	private void SetScaleDelta( ColliderHolder collider, Vector3 scaleDelta, Vector3 scalePivot, Quaternion scaleRotation )
	{
		SetPositionDelta( collider, scaleRotation * Vector3.Scale( Quaternion.Inverse( scaleRotation ) * ( collider.snapshotPosition - scalePivot ), scaleDelta ) + scalePivot - collider.snapshotPosition );

		float biggestDot = Mathf.NegativeInfinity;
		Quaternion refAlignment = Quaternion.identity;
		for( int i = 0; i < refAlignments.Length; i++ )
		{
			float dot = Mathf.Min(
				Mathf.Abs( Vector3.Dot( scaleRotation * Vector3.right, collider.snapshotRotation * refAlignments[i] * Vector3.right ) ),
				Mathf.Abs( Vector3.Dot( scaleRotation * Vector3.up, collider.snapshotRotation * refAlignments[i] * Vector3.up ) ),
				Mathf.Abs( Vector3.Dot( scaleRotation * Vector3.forward, collider.snapshotRotation * refAlignments[i] * Vector3.forward ) )
			);

			if( dot > biggestDot )
			{
				biggestDot = dot;
				refAlignment = refAlignments[i];
			}
		}

		scaleDelta = refAlignment * scaleDelta;
		scaleDelta = Vector3.Scale( scaleDelta, refAlignment * Vector3.one );

		collider.scale = Vector3.Scale( collider.snapshotScale, scaleDelta );
	}

	// Credit: https://github.com/Unity-Technologies/UnityCsReference/blob/61f92bd79ae862c4465d35270f9d1d57befd1761/Editor/Mono/GUI/Tools/TransformManipulator.cs#L148-L219
	private void SetPositionDelta( ColliderHolder collider, Vector3 positionDelta )
	{
		Vector3 newPosition = collider.snapshotPosition + positionDelta;
#if UNITY_2020_1_OR_NEWER
		if( !( (bool) incrementalSnapActive.GetValue( null, null ) || (bool) gridSnapActive.GetValue( null, null ) || (bool) vertexSnapActive.GetValue( null, null ) ) )
#endif
		{
			Vector3 minDifference = (Vector3) minDragDifference.GetValue( null, null );

			newPosition.x = Mathf.Approximately( positionDelta.x, 0f ) ? collider.snapshotPosition.x : RoundBasedOnMinimumDifference( newPosition.x, minDifference.x );
			newPosition.y = Mathf.Approximately( positionDelta.y, 0f ) ? collider.snapshotPosition.y : RoundBasedOnMinimumDifference( newPosition.y, minDifference.y );
			newPosition.z = Mathf.Approximately( positionDelta.z, 0f ) ? collider.snapshotPosition.z : RoundBasedOnMinimumDifference( newPosition.z, minDifference.z );
		}

		collider.surfacePosition = newPosition;
	}

	// Credit: https://github.com/Unity-Technologies/UnityCsReference/blob/61f92bd79ae862c4465d35270f9d1d57befd1761/Editor/Mono/Utils/MathUtils.cs#L68-L73
	private float RoundBasedOnMinimumDifference( float valueToRound, float minDifference )
	{
		if( minDifference == 0 )
		{
			int decimals = Mathf.Clamp( (int) ( 5 - Mathf.Log10( Mathf.Abs( valueToRound ) ) ), 0, 15 );
			return (float) System.Math.Round( valueToRound, decimals, System.MidpointRounding.AwayFromZero );
		}

		return (float) System.Math.Round( valueToRound, Mathf.Clamp( -Mathf.FloorToInt( Mathf.Log10( Mathf.Abs( minDifference ) ) ), 0, 15 ), System.MidpointRounding.AwayFromZero );
	}
	#endregion
}
#endif

How To

Simply create a C# script called BoxColliderWizard inside your Project window and copy this code inside it. Then, add Box Collider Wizard component to a GameObject in your scene. When that GameObject is selected, you can edit its child colliders or add new child colliders to it.

nice