RoApp/Assets/Editor/UI/ShapeEditor/RectSelectionTool.cs

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

public class RectSelectionTool
{
    Vector3 m_StartPoint;
    Rect m_Rect;
    GUIStyle m_GuiStyle;
    public Rect Do(int controlId, Vector3 origin)
    {
        if (m_GuiStyle == null)
            m_GuiStyle = GUI.skin.FindStyle("selectionRect");
        Handles.BeginGUI();
        Event currentEvent = Event.current;
        Ray ray = HandleUtility.GUIPointToWorldRay(currentEvent.mousePosition);
        Vector3 forward = Camera.current.transform.forward;
        Vector3 up = Camera.current.transform.up;
        Vector3 right = Camera.current.transform.right;
        Plane plane = new Plane(forward, origin);
        float distance;
        if (!plane.Raycast(ray, out distance))
            return new Rect();
        Vector3 worldPoint = ray.GetPoint(distance);
        EventType eventType = currentEvent.GetTypeForControl(controlId);
        if (eventType == EventType.Layout)
            HandleUtility.AddDefaultControl(controlId);
        if (eventType == EventType.MouseDown && currentEvent.button == 0)
        {
            m_StartPoint = worldPoint;
            m_Rect = new Rect(m_StartPoint, Vector3.zero);
        }
        if (GUIUtility.hotControl == controlId && eventType == EventType.Repaint)
            m_GuiStyle.Draw(m_Rect, GUIContent.none, false, false, false, false);
        EditorGUI.BeginChangeCheck();
        worldPoint = Handles.Slider2D(controlId, worldPoint, forward, up, right, 1f, (int cid, Vector3 p, Quaternion q, float s, EventType et) => { }, Vector2.zero);
        if (EditorGUI.EndChangeCheck())
            m_Rect = FromToRect(HandleUtility.WorldToGUIPoint(m_StartPoint), HandleUtility.WorldToGUIPoint(worldPoint));
        Handles.EndGUI();
        return m_Rect;
    }
    Rect FromToRect(Vector2 start, Vector2 end)
    {
        Rect r = new Rect(start.x, start.y, end.x - start.x, end.y - start.y);
        if (r.width < 0)
        {
            r.x += r.width;
            r.width = -r.width;
        }
        if (r.height < 0)
        {
            r.y += r.height;
            r.height = -r.height;
        }
        return r;
    }
}