解决UnityGLTF不支持Android手机端不能读取StreamingAssets目录下文件的问题

最近工作比较忙，已经2个多月没有写博客了。最近一直在一个VR办公会议的项目，也积累了一些东东需要写出来。

在项目中用到了gltf资源，用到UntiyGLTF这个开源工具，用来在云上或者StreamingAssets目录下读取文件，并且渲染出来。

但是在使用UnityGLTF时，在Android手机上，不支持读取StreamingAssets目录下的gltf文件。所以写个UnityWebRequestLoader来支持读取文件，使用了Unity的自带的WebRequest。

1、首先UnityWebRequest不支持await等待，需要进行对他进行扩展支持

    public static class UnityGLTFExtension {
        public static TaskAwaiter GetAwaiter(this AsyncOperation asyncOp)
        {
            var tcs = new TaskCompletionSource<object>();
            asyncOp.completed += obj => { tcs.SetResult(null); };
            return ((Task)tcs.Task).GetAwaiter();
        }
    }

2、增加UnityWebRequestLoader的loader插件，支持android读取StreamingAssets目录下的文件

using System;
using System.IO;
using System.Runtime.CompilerServices;
using System.Threading.Tasks;
using UnityEngine;
using UnityEngine.Networking;

namespace UnityGLTF.Loader
{
    public static class UnityGLTFExtension {
        public static TaskAwaiter GetAwaiter(this AsyncOperation asyncOp)
        {
            var tcs = new TaskCompletionSource<object>();
            asyncOp.completed += obj => { tcs.SetResult(null); };
            return ((Task)tcs.Task).GetAwaiter();
        }
    }


    public class UnityWebRequestLoader : ILoader
    {
        public Stream LoadedStream { get; private set; }

        public bool HasSyncLoadMethod => false;

        private string _rootUri;

        public UnityWebRequestLoader(string rootUri)
        {
            _rootUri = rootUri;
        }


        public async Task LoadStream(string gltfFilePath)
        {
            if (gltfFilePath == null)
            {
                throw new ArgumentNullException(nameof(gltfFilePath));
            }

            string pathToLoad = Path.Combine(_rootUri, gltfFilePath);

            var getRequest = UnityWebRequest.Get(pathToLoad);
            await getRequest.SendWebRequest();

            byte[] data = getRequest.downloadHandler.data;
            if (data == null || data.Length == 0)
            {
                throw new InvalidOperationException(string.Format(
                    "Failed to load from '{0}' - file was empty!", pathToLoad));
            }
            LoadedStream = new MemoryStream(data.Length);
            await LoadedStream.WriteAsync(data, 0, data.Length);
        }

        public void LoadStreamSync(string jsonFilePath)
        {
            throw new NotImplementedException();
        }
    }
}

3、包装一下gltf load，支持http/https，android手机加载，普通pc加载

    public static async Task<GameObject> Load(string gltfUrl, Transform parent)
    {
        GameObject obj = null;
        GLTFSceneImporter sceneImporter = null;
        ILoader loader = null;
        string directoryPath = URIHelper.GetDirectoryName(gltfUrl);
        try
        {
            if (gltfUrl.StartsWith("http://") || gltfUrl.StartsWith("https://"))
            {
                loader = new WebRequestLoader(directoryPath);

                sceneImporter = new GLTFSceneImporter(
                    URIHelper.GetFileFromUri(new Uri(gltfUrl)),
                    loader,
                    asyncCoroutineHelper
                    );
            }
            else if (gltfUrl.StartsWith("jar:file://"))
            {
                loader = new UnityWebRequestLoader(directoryPath);

                sceneImporter = new GLTFSceneImporter(
                    Path.GetFileName(gltfUrl),
                    loader,
                    asyncCoroutineHelper
                    );
            }
            else
            {
                loader = new FileLoader(directoryPath);
                sceneImporter = new GLTFSceneImporter(
                    Path.GetFileName(gltfUrl),
                    loader,
                    asyncCoroutineHelper
                    );
            }

            sceneImporter.SceneParent = parent;
            sceneImporter.Collider = GLTFSceneImporter.ColliderType.None;
            sceneImporter.MaximumLod = 300;
            sceneImporter.IsMultithreaded = true;

            await sceneImporter.LoadSceneAsync();

            obj = sceneImporter.CreatedObject;
        }
        finally
        {
            if (loader != null)
            {
                sceneImporter?.Dispose();
                sceneImporter = null;
                loader = null;
            }
        }

        return obj;
    }

4、根据不同的平台，组装streamingassets目录

    private string streamingAssetsPath;
        streamingAssetsPath =
#if UNITY_EDITOR
            Application.streamingAssetsPath;
#else
            "jar:file://" + Application.dataPath + "!/assets";
#endif

GameObject rootObject = await Gltf.Load(streamingAssetsPath + "test.glb", parentTransform);

这样就可以支持android手机也可以在StreamingAssets目录下读取gltf/glb文件了。