[Editor scripting] How to save a script generated mesh as an asset/FBX?

I wrote a small editor script that adds a context menu item to the MeshFilter component. It will allow you to save the mesh in the MeshFilter as a .asset file, which you can drag into any GameObject with a MeshRenderer and MeshFilter and it will work.

https://github.com/pharan/Unity-MeshSaver/blob/master/MeshSaver/Editor/MeshSaverEditor.cs

You can also check the code to see how it was done.

There is a method not involving generation of intermediate files: have a prefab template that looks almost ready and only misses a mesh. You can then either save your mesh into this prefab and assign it to MeshFilter's sharedMesh or (useful if you want to generate multiple meshes into identical prefab) go something like:

// All generated models will be structured after this template string modelTemplate = "Assets/Templates/Model.prefab";

 // this way links will persist when we regenerate the mesh
 Object prefab = AssetDatabase.LoadAssetAtPath(prefabPath, typeof(GameObject));
 if (!prefab) {
     prefab = EditorUtility.CreateEmptyPrefab( prefabPath );
 }

 // sort of the same...
 Mesh mesh = (Mesh)AssetDatabase.LoadAssetAtPath(prefabPath, typeof(Mesh));
 if (!mesh) {
     mesh = new Mesh();
     mesh.name = name;
     AssetDatabase.AddObjectToAsset (mesh, prefabPath);
 } else {
     mesh.Clear();
 }
 // generate your mesh in place
 BlaBlaBla(mesh);
 // assume that MeshFilter is already there. could check and AddComponent
 template.GetComponent<MeshFilter>().sharedMesh = mesh;

 // make sure 
 EditorUtility.ReplacePrefab(template, prefab, ReplacePrefabOptions.ReplaceNameBased);
 // get rid of the temporary object (otherwise it stays over in scene)
 Object.DestroyImmediate(template);

This is not generalized enough yet (contains a call to BlaBlaBla :-) - mesh generation function), you really should pass some sort of generator object to this function or something like that. It's because I adapted this snippet from my working code that does something slightly different. Now that I realize that it's generalizable I'll probably refactor it next time I have some time to kill.

This code makes sure that if you've instantiated your models already and decide to regenerate the mesh prefab link will stay intact. On the other hand, model is not linked to the template, if you change the template you will have to regenerate all models you have (and their instances will get updated then).

I had some old .asset files of Mesh data that I wanted to make accessible for external editing as FBX files. I was able to use the SDK provided in https://assetstore.unity.com/packages/essentials/101408 to write my own context menu option for Mesh .asset files. The SDK enabled a large amount of control, such as saving as ascii or binary format , changing the scale and axis orientation, etc.

You can use the ExtractToFBX function in the code below to save any dynamically generated mesh (you must provide a filepath) or serialized Mesh asset file to an FBX:

 using System.IO;
 using UnityEngine;
 using UnityEditor;
 using Unity.FbxSdk;
 using FbxExporters.Editor;
 
 // Place in 'Editor' folder
 public static class ExtractMeshToFBX
 {
     // true: fbx file is easy-to-debug ascii, false: fbx file is binary.
     static bool saveFbxAsAscii = false;
 
     // The preferred axis system for the exported fbx file
     static FbxAxisSystem fbxAxisSystem = FbxAxisSystem.Max;
     // The preferred units of the exported fbx file
     static FbxSystemUnit fbxUnit = FbxSystemUnit.m;
 
     static string fbxFileTitle       = "TITLE HERE";
     static string fbxFileSubject     = "SUBJECT HERE";
     static string fbxFileComment     = "COMMENT HERE";
     static string fbxFileKeywords    = "KEYWORDS HERE";
     static string fbxFileAuthor      = "AUTHOR HERE";
     static string fbxFileRevision    = "1.0";
     static string fbxFileApplication = "Unity FBX SDK";
 
 
     [MenuItem("Assets/Extract to FBX", validate = true)]
     public static bool MenuExtractToFBXValidate()
     {
         if (Selection.activeObject == null)
             return false;
         return Selection.activeObject.GetType() == typeof(Mesh);
     }
 
     [MenuItem("Assets/Extract to FBX")]
     public static void MenuExtractToFBX()
     {
         // We assume validation worked and this is always defined.
         Mesh mesh = Selection.activeObject as Mesh;
 
         // Set up paths
         string meshFilePath = AssetDatabase.GetAssetPath(mesh);
         string meshDirectory = Path.GetDirectoryName(meshFilePath);
 
         string filename = Path.GetFileNameWithoutExtension(meshFilePath) + ".fbx";
         string filePath = Path.Combine(meshDirectory, filename);
 
         ExtractToFBX(mesh, filePath);
     }
 
     public static void ExtractToFBX(Mesh mesh, string filePath)
     {
         // Make a temporary copy of the mesh to modify it
         Mesh tempMesh = Object.Instantiate(mesh);
         tempMesh.name = mesh.name;
 
         // If meters, divide by 100 since default is cm. Assume centered at origin.
         if (fbxUnit == FbxSystemUnit.m)
         {
             Vector3[] vertices = tempMesh.vertices;
             for (int i = 0; i < vertices.Length; ++i)
                 vertices[i] /= 100.0f;
             tempMesh.vertices = vertices;
         }
         // You could handle other SystemUnits here
 
         // FBX Manager
         FbxManager manager = FbxManager.Create();
         manager.SetIOSettings(FbxIOSettings.Create(manager, Globals.IOSROOT));
 
         // FBX Exporter
         FbxExporter fbxExporter = FbxExporter.Create(manager, "Exporter");
 
         // Binary
         int fileFormat = -1;
         // Ascii
         if (saveFbxAsAscii)
             fileFormat = manager.GetIOPluginRegistry().FindWriterIDByDescription("FBX ascii (*.fbx)");
 
         fbxExporter.Initialize(filePath, fileFormat, manager.GetIOSettings());
         fbxExporter.SetFileExportVersion("FBX201400");
 
         // FBX Scene
         FbxScene fbxScene = FbxScene.Create(manager, "Scene");
         FbxDocumentInfo sceneInfo = FbxDocumentInfo.Create(manager, "SceneInfo");
 
         // Set up scene info
         sceneInfo.mTitle    = fbxFileTitle;
         sceneInfo.mSubject  = fbxFileSubject;
         sceneInfo.mComment  = fbxFileComment;
         sceneInfo.mAuthor   = fbxFileAuthor;
         sceneInfo.mRevision = fbxFileRevision;
         sceneInfo.mKeywords = fbxFileKeywords;
         sceneInfo.Original_ApplicationName.Set(fbxFileApplication);
         sceneInfo.LastSaved_ApplicationName.Set(fbxFileApplication);
         fbxScene.SetSceneInfo(sceneInfo);
 
         // Set up Global settings
         FbxGlobalSettings globalSettings = fbxScene.GetGlobalSettings();
         globalSettings.SetSystemUnit(fbxUnit);
         globalSettings.SetAxisSystem(fbxAxisSystem);
 
         FbxNode modelNode = FbxNode.Create(fbxScene, tempMesh.name);
         // Add mesh to a node in the scene
         using (ModelExporter modelExporter = new ModelExporter())
         {
             if (!modelExporter.ExportMesh(tempMesh, modelNode))
                 Debug.LogError("Problem Exporting Mesh");
         }
         // add the model to the scene
         fbxScene.GetRootNode().AddChild(modelNode);
 
         // Finally actually save the scene
         bool sceneSuccess = fbxExporter.Export(fbxScene);
         AssetDatabase.Refresh();
 
         // clean up temporary model
         if (Application.isPlaying)
             Object.Destroy(tempMesh);
         else
             Object.DestroyImmediate(tempMesh);
     }
 }

The code worked even on 2017.1 despite the above package requiring 2017.3, after first downloading the package in a later version and then manually moving the DLLs. The dependency on 2017.3 is only due to their custom UI, which this code does not use.

If you want to include materials in the fbx you can easily modify the function to pass in materials which can be passed in as an argument to modelExporter.ExportMesh.