A Unity Editor extension to generate draggable points for vector3 serialized attributes.

DraggablePoint.cs

using System;
using UnityEngine;
#if UNITY_EDITOR
using UnityEditor;
#endif

public class DraggablePoint : PropertyAttribute {}


#if UNITY_EDITOR
[CustomEditor(typeof(MonoBehaviour), true)]
public class DraggablePointDrawer : Editor {

  readonly GUIStyle style = new GUIStyle();

  void OnEnable(){
    style.fontStyle = FontStyle.Bold;
    style.normal.textColor = Color.white;
  }

  public void OnSceneGUI () {
    var property = serializedObject.GetIterator ();
    while (property.Next (true)) {
      if (property.propertyType == SerializedPropertyType.Vector3) {
        var field = serializedObject.targetObject.GetType ().GetField (property.name);
        if (field == null) {
          continue;
        }
        var draggablePoints = field.GetCustomAttributes (typeof(DraggablePoint), false);
        if (draggablePoints.Length > 0) {
          Handles.Label(property.vector3Value, property.name);
          property.vector3Value = Handles.PositionHandle (property.vector3Value, Quaternion.identity);
          serializedObject.ApplyModifiedProperties ();
        }
      }
    }
  }
}
#endif

ExampleBehavior.cs

using UnityEngine;
using System.Collections;

public class ExampleBehavior : MonoBehaviour {
  [DraggablePoint] public Vector3 SpawnPosition;
  public GameObject SpawnableObject;

  public void Spawn() {
    Instantiate(SpawnableObject, SpawnPosition, Quaternion.identity);
  }
}

How can you do the same but for Arrays or Lists of Vector3? Thank you.

Sorry accidentally didn't comment to you directly but have a look at my comment:
https://gist.github.com/ProGM/226204b2a7f99998d84d755ffa1fb39a#gistcomment-3266712

Soooo back again.... Made another version that puts handles relative to the parent. So if you move the game object around the handles will move relative to the parent rather than being in world space.

using System;
using UnityEngine;
using System.Reflection;
#if UNITY_EDITOR
using UnityEditor;
#endif

///Handles relative to game object
public class DraggablePointRelative : PropertyAttribute { }


#if UNITY_EDITOR
[CustomEditor(typeof(MonoBehaviour), true)]
public class DraggablePointDrawer : Editor
{

    readonly GUIStyle style = new GUIStyle();

    void OnEnable()
    {
        style.fontStyle = FontStyle.Bold;
        style.normal.textColor = Color.white;
    }

    public void OnSceneGUI()
    {
        SerializedProperty property = serializedObject.GetIterator();
        while (property.Next(true))
        {
            if (property.propertyType == SerializedPropertyType.Vector3)
            {
                handleVectorProperty(property);
            }
            else if (property.isArray)
            {
                for (int x = 0; x < property.arraySize; x++)
                {
                    SerializedProperty element = property.GetArrayElementAtIndex(x);
                    if (element.propertyType != SerializedPropertyType.Vector3)
                    {
                        //Break early if we're not an array of Vector3
                        break;
                    }
                    handleVectorPropertyInArray(element, property, x);
                }
            }
        }
    }

    void handleVectorProperty(SerializedProperty property)
    {
        FieldInfo field = serializedObject.targetObject.GetType().GetField(property.name);
        if (field == null)
        {
            return;
        }
        var draggablePoints = field.GetCustomAttributes(typeof(DraggablePoint), false);
        if (draggablePoints.Length > 0)
        {
            Handles.Label(property.vector3Value + ((MonoBehaviour)target).transform.position, property.name);
            property.vector3Value = Handles.PositionHandle(property.vector3Value + ((MonoBehaviour)target).transform.position, Quaternion.identity) - ((MonoBehaviour)target).transform.position;
            serializedObject.ApplyModifiedProperties();
        }
    }

    void handleVectorPropertyInArray(SerializedProperty property, SerializedProperty parent, int index)
    {
        FieldInfo parentfield = serializedObject.targetObject.GetType().GetField(parent.name);
        if (parentfield == null)
        {
            return;
        }
        var draggablePoints = parentfield.GetCustomAttributes(typeof(DraggablePoint), false);
        if (draggablePoints.Length > 0)
        {
            Handles.Label(property.vector3Value + ((MonoBehaviour)target).transform.position, parent.name + "[" + index + "]");
            property.vector3Value = Handles.PositionHandle(property.vector3Value + ((MonoBehaviour)target).transform.position, Quaternion.identity) - ((MonoBehaviour)target).transform.position;
            serializedObject.ApplyModifiedProperties();
        }
    }
}
#endif

public class DraggablePoint : PropertyAttribute {} should not be defined in a script inside the Editor folder but somewhere inside a Script or Assets folder. Otherwise you'll be forced to place all the script using this inside the Editor folder

I realise I'm replying a year and a half later, but I'm trying to adapt this to be able to edit Vector3 arrays in scriptable objects. I'm using SOs to generate spawn points for a mobile game and being able to edit them quickly in the scene view would be useful, rather than doing so in the inspector.

I'm assuming I need to use the OnOpenAsset to access assets as opposed to game objects but I keep hitting brick walls. Anybody managed to do this?