Loads all 3D models from a folder and saves them as prefabs.

ModelToPrefabBatchConverter.cs

// Model to Prefab Batch Converter for Unity
// Loads all 3D models from a folder and saves them as prefabs.
// by Andy Miira (Andrei Müller), October 2019
//
//
// [INSTRUCTIONS]
// 0) Add this script inside an "Editor" folder in your project.
// You must create this folder if it doesn't already exist.
//
// 1) Open Unity, then click on
// "Tools -> Mirror Mirai -> Model to Prefab Batch Converter" at the menu bar.
//
// 2) Type or paste the paths for the Models Folder (where the source models are located)
// and Prefabs Folder (where the resulting prefabs will be saved).
//
// For example, if your models are located at Assets/Art/Models, you can use the paths:
// Models Folder: Assets/Art/Models
// Prefabs Folder: Assets/Art/Prefabs (if this folder doesn't exist, it will be created)
//
// TIP: In Unity's Project tab, you can left-click on a folder to select it,
// then right-click on it and select the option "Copy Path".
// After that, you can paste the path directly in the converter's Folder fields.
//
// 3) You can optionally add Colliders and Rigidbodies to the generated prefabs, by selecting the respective options.
//
// 4) Finally, click on the "Create Prefabs" button.
// The prefabs will be saved at the defined Prefabs Folder.
//
//
// Check out more Unity scripts and utilities at:
// https://gist.github.com/andreiagmu

using System.IO;
using UnityEditor;
using UnityEngine;

namespace MirrorMirai
{
    public class ModelToPrefabBatchConverter : ScriptableWizard
    {
        public enum ColliderType
        {
            None,
            SphereCollider,
            CapsuleCollider,
            BoxCollider,
            MeshCollider
        }

        public string modelsFolder;
        public string prefabsFolder;

        public ColliderType addCollider;
        public bool convexMeshCollider;
        public bool addRigidbody;
        public bool kinematicRigidbody;


        [MenuItem("Tools/Mirror Mirai/Model to Prefab Batch Converter")]
        static void CreateWizard()
        {
            DisplayWizard<ModelToPrefabBatchConverter>("Model to Prefab Batch Converter", "Create Prefabs");
        }

        void OnWizardCreate()
        {
            if (string.IsNullOrWhiteSpace(modelsFolder) || !Directory.Exists(modelsFolder)) {
                Debug.LogWarning("modelsFolder not set to a valid directory!");
                return;
            }

            if (string.IsNullOrWhiteSpace(prefabsFolder)) {
                Debug.LogWarning("You didn't set the prefabsFolder path!");
                return;
            }

            if (!Directory.Exists(prefabsFolder)) {
                Directory.CreateDirectory(prefabsFolder);
            }


            DirectoryInfo dir = new DirectoryInfo(modelsFolder);

            foreach (var fileInfo in dir.GetFiles()) {
                if (fileInfo.Name.EndsWith(".fbx")) {
                    var filename = Path.GetFileNameWithoutExtension(fileInfo.Name);

                    var modelRootGO = (GameObject)AssetDatabase.LoadMainAssetAtPath(modelsFolder + "/" + fileInfo.Name);
                    var instanceRoot = (GameObject)PrefabUtility.InstantiatePrefab(modelRootGO);
                    ResetTransform(instanceRoot.transform);

                    if (addRigidbody) {
                        var rigidbody = instanceRoot.AddComponent<Rigidbody>();
                        rigidbody.isKinematic = kinematicRigidbody;
                    }

                    if (addCollider == ColliderType.SphereCollider) {
                        var collider = instanceRoot.AddComponent<SphereCollider>();

                        var totalBounds = TotalBounds(instanceRoot.transform);
                        collider.center = totalBounds.center;
                        collider.radius = Vector3.Distance(totalBounds.center, totalBounds.extents);
                    }
                    else if (addCollider == ColliderType.CapsuleCollider) {
                        var collider = instanceRoot.AddComponent<CapsuleCollider>();

                        var totalBounds = TotalBounds(instanceRoot.transform);
                        collider.center = totalBounds.center;
                        collider.radius = Vector3.Distance(totalBounds.center, totalBounds.extents);
                        collider.height = totalBounds.size.y;
                    }
                    else if (addCollider == ColliderType.BoxCollider) {
                        var collider = instanceRoot.AddComponent<BoxCollider>();

                        var totalBounds = TotalBounds(instanceRoot.transform);
                        collider.center = totalBounds.center;
                        collider.size = totalBounds.size;
                    }
                    else if (addCollider == ColliderType.MeshCollider) {
                        var objMeshes = instanceRoot.GetComponentsInChildren<MeshFilter>();

                        foreach (var mesh in objMeshes) {
                            var collider = mesh.gameObject.AddComponent<MeshCollider>();
                            collider.convex = convexMeshCollider;
                        }
                    }

                    PrefabUtility.SaveAsPrefabAsset(instanceRoot, prefabsFolder + "/" + filename + ".prefab");

                    DestroyImmediate(instanceRoot);
                }
            }
        }

        void ResetTransform(Transform t)
        {
            t.position = Vector3.zero;
            t.rotation = Quaternion.identity;
            t.localScale = Vector3.one;
        }

        Bounds TotalBounds(Transform root)
        {
            Renderer[] renderers = root.GetComponentsInChildren<Renderer>();
            Bounds bounds = renderers[0].bounds;

            for(int i = 1; i < renderers.Length; ++i)
            {
                bounds.Encapsulate(renderers[i].bounds.min);
                bounds.Encapsulate(renderers[i].bounds.max);
            }

            return bounds;
        }
    }
}