How to setup automatic LODs inside Unity?

[ludwigseibt]

Describe the bug 💬

Is it currently possible to automatically setup LODs inside Unity in a similar way to how fbx does it?

For example exporting a fbx with 3 objects named ..._LOD0, ..._LOD1, ..._LOD2 would automatically setup an LOD group in Unity.

An example for the workflow to do this with Blender would be helpful.

Steps to reproduce 🔢

1. Export mesh with LODs from Blender
2. Import into Unity and automatically setup LOD Group

Files to reproduce the issue ♻

No response

Editor Version 🎲

6000.0

Render Pipeline and version

URP 17.0.4

UnityGLTF Version

2.16.0

Operating System 👩‍💻

Windows

When does this problem happen?

• Editor Import
• Runtime Import
• Editor Export
• Runtime Export

Additional Info 📜

No response

Validations 🩹

• I have searched existing issues: no issue already exist that reports the same problem.
• I follow the Code of Conduct
• I provided a minimal reproducible example, including files when necessary.

[marwie]

You could create an importer plugin to do this and add components on import

See the audio plugin as an example: https://github.com/KhronosGroup/UnityGLTF/blob/main/Runtime/Scripts/Plugins/Experimental/AudioImport.cs

There are various hooks that you can use form within your plugin: https://github.com/KhronosGroup/UnityGLTF/blob/main/Runtime/Scripts/Plugins/Core/GltfImportPlugin.cs#L18

[XtroTheArctic]

No custom importer is needed for this. Here is how I do it using Blender and "glTF-Blender-IO-MSFT-lod" addon (with the fix from PR for Blender 4 support): takahirox/glTF-Blender-IO-MSFT-lod#5

When I export the model in this setup, UnityGLTF correctly creates the LOD component in Unity.

[hybridherbst]

@pfcDorn has started some work on adding a LOD-by-names plugin, but it hasn't been completed yet.
In the meantime, using the MSFT_lods extension as outlined above is a great approach.

[ludwigseibt]

Hey everyone. Thanks for the suggestions.
I created my own importer plugin. LOD transitions are hardcoded, you might want to change that for your project. It works with the "_LOD0", 1, 2, 3 suffix and also ignores Blenders ".001", 002, ... suffixes that get added on duplicate objects. The LOD objects should have a common parent to take the LOD group. This can be easily changed if you want the LOD group on the LOD0 Object instead.

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;
using GLTF.Schema;
using UnityEngine;
using UnityEngine.Networking;
#if UNITY_EDITOR
using UnityEditor;
#endif

namespace UnityGLTF.Plugins
{
    public class LODGroupSetupGltfPlugin : GLTFImportPlugin 
    {
        public override bool EnabledByDefault => true;
        public override bool AlwaysEnabled => false;
        public override string DisplayName => "LODGroupSetup";
        public override string Description => "Automatically setup LOD Groups via _LOD0/1/2 object name suffixes.";

        public override GLTFImportPluginContext CreateInstance(GLTFImportContext context)
        {
            return new LODGroupSetupGltfPluginContext();
        }
    }

    public class LODGroupSetupGltfPluginContext : GLTFImportPluginContext
    {
        static float[] lodTransitions = { .5f, .2f, .1f, .001f};
        string lod0Regex = @"_LOD0(?:\.\d{3})?$";
        string lodRegex = @"_LOD\d(?:\.\d{3})?$";
        List<Transform> lodCandidates = new List<Transform>();

        public override void OnAfterImportNode(Node node, int nodeIndex, GameObject nodeObject)
        {
            if (Regex.IsMatch(nodeObject.name, lod0Regex))
            {
                lodCandidates.Add(nodeObject.transform);
            }
        }

        public override void OnAfterImportScene(GLTFScene scene, int sceneIndex, GameObject sceneObject)
        {
            SetupLODGroups(lodCandidates);
        }

        void SetupLODGroups(List<Transform> lodCandidates)
        {
            foreach (Transform obj in lodCandidates)
            {
                string baseName = Regex.Replace(obj.name,lodRegex, String.Empty);
                GameObject lodParent = obj.transform.parent.gameObject;
                List<Transform> lodObjects = new List<Transform>();
                foreach (Transform child in lodParent.transform)
                {
                    if (Regex.Replace(child.name,lodRegex, String.Empty) == baseName)
                    {
                        lodObjects.Add(child);
                    }
                }

                if (lodObjects.Count > 1)
                {
                    LODGroup lodGroupComponent = lodParent.GetComponent<LODGroup>();
                    if (lodGroupComponent == null)
                    {
                        lodGroupComponent = lodParent.AddComponent<LODGroup>();
                    }

                    LOD[] lods = new LOD[lodObjects.Count];
                    for (int i = 0; i < lodObjects.Count; i++)
                    {
                        Renderer renderer = lodObjects[i].GetComponent<Renderer>();
                        if (renderer != null)
                        {
                            float lodTransition = i < lodObjects.Count - 1 ? lodTransitions[i] : lodTransitions.Last();
                            lods[i] = new LOD(lodTransition, new Renderer[] { renderer });
                        }
                    }

                    lodGroupComponent.SetLODs(lods);
                    lodGroupComponent.RecalculateBounds();
                }
            }
        }
    }
}

[robertdorn83]

Nice! would you like to share this plugin with a PR?

[ludwigseibt]

It would need some more polishing. I dont have the time to do that at the moment, sorry. Might come back to it later.

[ludwigseibt]

@hybridherbst We are investing some more time into this plugin, but I have a few questions.

To make LOD crossfade work, we need to enable the "Supports LOD Crossfade" checkbox inside the PBRGraph shader. Should we enable this by default in the package? I am unsure wether this will cost performance when no LOD Crossfade is used. Currently we are using an overwritten version of the PBRGraph in our project to enable this feature.

Is there a way to expose per object import settings for my import extension? I would like to be able to chose LOD "Fade mode", "Animate Crossfade" and the fade times per imported object.

Thanks a lot!