DimensionsTool.cs

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

public class DimensionsTool : EditorWindow {
    Bounds bounds = new Bounds();
    long polygons = 0;
    int count = 0;
    bool drawBox = false;
    SelectionMode sm = SelectionMode.Deep | SelectionMode.Editable;

    Vector3 centerPoint;

    // Add menu item named "My Window" to the Window menu
    [MenuItem("Window/Dimension Tool")]
    public static void Init() {
        //Show existing window instance. If one doesn't exist, make one.
        DimensionsTool window = (DimensionsTool)EditorWindow.GetWindow(typeof(DimensionsTool));

        SceneView.onSceneGUIDelegate -= window.OnSceneGUI;
        SceneView.onSceneGUIDelegate += window.OnSceneGUI;

        window.Show();
    }

    void OnEnable() {
        SceneView.onSceneGUIDelegate += OnSceneGUI;
    }
    void OnDisable() {
        SceneView.onSceneGUIDelegate -= OnSceneGUI;
    }

    void OnSelectionChange() {
        MeshFilter[] filters = Selection.GetFiltered<MeshFilter>(sm);

        MeshRenderer[] renderers = Selection.GetFiltered<MeshRenderer>(sm);

        bounds = new Bounds();
        polygons = 0;
        count = 0;
        centerPoint = Vector3.zero;

        /*foreach(MeshRenderer mr in renderers) {
            bounds.Encapsulate(mr.bounds);
        }*/

        if (renderers.Length > 0) {
            foreach(MeshFilter mf in filters) {
                polygons += mf.sharedMesh.triangles.LongLength;
            }

            foreach (MeshRenderer r in renderers) {
                count++;
                if (r.bounds != null) {
                    centerPoint += r.transform.position;
                }
            }

            centerPoint /= count;

            bounds.center = centerPoint;

            foreach (MeshRenderer r in renderers) {
                if (r.bounds != null) {
                    Bounds temp = r.bounds;

                    bounds.Encapsulate(temp);
                }
            }
        }

        Repaint();
    }

    void OnGUI() {
        GUILayout.Label("Dimensions", EditorStyles.boldLabel);
        
        GUILayout.Label("Objects Selected " + count, EditorStyles.label);
        GUILayout.Label("Triangles " + polygons, EditorStyles.label);
        //EditorGUILayout.Vector3Field("Bounds", bounds.size);

        sm = (SelectionMode)EditorGUILayout.EnumMaskField("Selection Filter", sm);

        color = EditorGUILayout.ColorField(color);
        drawBox = EditorGUILayout.Toggle("Draw Bounds?", drawBox);

        EditorGUILayout.Vector3Field("Size", bounds.size);

        /*groupEnabled = EditorGUILayout.BeginToggleGroup("Optional Settings", groupEnabled);
        myBool = EditorGUILayout.Toggle("Toggle", myBool);
        myFloat = EditorGUILayout.Slider("Slider", myFloat, -3, 3);
        EditorGUILayout.EndToggleGroup();*/
    }

    private Color color = Color.magenta;

    private Vector3 v3FrontTopLeft;
    private Vector3 v3FrontTopRight;
    private Vector3 v3FrontBottomLeft;
    private Vector3 v3FrontBottomRight;
    private Vector3 v3BackTopLeft;
    private Vector3 v3BackTopRight;
    private Vector3 v3BackBottomLeft;
    private Vector3 v3BackBottomRight;

    void OnSceneGUI(SceneView sceneView) {
        if (drawBox) {
            Handles.color = color;

            //Debug.Log("DrawingBox");

            DrawBox();
        }
    }

    void CalcPositons() {
        //Bounds bounds;
        //BoxCollider bc = GetComponent<BoxCollider>();
        //if (bc != null)
        //    bounds = bc.bounds;
        //else
        //return;

        Vector3 v3Center = bounds.center;
        Vector3 v3Extents = bounds.extents;

        v3FrontTopLeft = new Vector3(v3Center.x - v3Extents.x, v3Center.y + v3Extents.y, v3Center.z - v3Extents.z);  // Front top left corner
        v3FrontTopRight = new Vector3(v3Center.x + v3Extents.x, v3Center.y + v3Extents.y, v3Center.z - v3Extents.z);  // Front top right corner
        v3FrontBottomLeft = new Vector3(v3Center.x - v3Extents.x, v3Center.y - v3Extents.y, v3Center.z - v3Extents.z);  // Front bottom left corner
        v3FrontBottomRight = new Vector3(v3Center.x + v3Extents.x, v3Center.y - v3Extents.y, v3Center.z - v3Extents.z);  // Front bottom right corner
        v3BackTopLeft = new Vector3(v3Center.x - v3Extents.x, v3Center.y + v3Extents.y, v3Center.z + v3Extents.z);  // Back top left corner
        v3BackTopRight = new Vector3(v3Center.x + v3Extents.x, v3Center.y + v3Extents.y, v3Center.z + v3Extents.z);  // Back top right corner
        v3BackBottomLeft = new Vector3(v3Center.x - v3Extents.x, v3Center.y - v3Extents.y, v3Center.z + v3Extents.z);  // Back bottom left corner
        v3BackBottomRight = new Vector3(v3Center.x + v3Extents.x, v3Center.y - v3Extents.y, v3Center.z + v3Extents.z);  // Back bottom right corner
        
    }

    void DrawBox() {
        CalcPositons();


        //if (Input.GetKey (KeyCode.S)) {
        Handles.DrawLine(v3FrontTopLeft, v3FrontTopRight);
        Handles.DrawLine(v3FrontTopRight, v3FrontBottomRight);
        Handles.DrawLine(v3FrontBottomRight, v3FrontBottomLeft);
        Handles.DrawLine(v3FrontBottomLeft, v3FrontTopLeft);
        Handles.DrawLine(v3BackTopLeft, v3BackTopRight);
        Handles.DrawLine(v3BackTopRight, v3BackBottomRight);
        Handles.DrawLine(v3BackBottomRight, v3BackBottomLeft);
        Handles.DrawLine(v3BackBottomLeft, v3BackTopLeft);
        Handles.DrawLine(v3FrontTopLeft, v3BackTopLeft);
        Handles.DrawLine(v3FrontTopRight, v3BackTopRight);
        Handles.DrawLine(v3FrontBottomRight, v3BackBottomRight);
        Handles.DrawLine(v3FrontBottomLeft, v3BackBottomLeft);
        //}
    }
}