Editor.OnSceneGUI()

Description

Enables the Editor to handle an event in the Scene view.

In the OnSceneGUI you can do for example mesh editing, terrain painting or advanced gizmos. If Event.current.Use() is called the event will be "eaten" by the editor and not be used by the Scene view itself.

In the following two scripts OnSceneGUI is used to draw lines between game objects. The first script shows how OnSceneGUI is used. In this script a game object is used as a parent. The position of the parent is obtained and then lines are draw from this to game objects stored in an array. The Handles.DrawLine function is used for this. The documentation for Handles.DrawLine has a very similar example.

using UnityEngine;
using UnityEditor;

[CustomEditor( typeof( DrawLine ) )]
public class DrawLineEditor : Editor
{
    // draw lines between a chosen game object
    // and a selection of added game objects

    void OnSceneGUI()
    {
        // get the chosen game object
        DrawLine t = target as DrawLine;

        if( t == null || t.GameObjects == null )
            return;

        // grab the center of the parent
        Vector3 center = t.transform.position;

        // iterate over game objects added to the array...
        for( int i = 0; i < t.GameObjects.Length; i++ )
        {
            // ... and draw a line between them
            if( t.GameObjects[i] != null )
                Handles.DrawLine( center, t.GameObjects[i].transform.position );
        }
    }
}

This script stores the array of game objects which will have a line drawn to them. This regular script is simply attached to a game object which is considered to be the starting point for all lines.

using UnityEngine;

[ExecuteInEditMode]
public class DrawLine : MonoBehaviour
{
    // an array of game objects which will have a
    // line drawn to in the Scene editor
    public GameObject[] GameObjects;
}