UsdViewHostLoader.cs

/* ========================================================================
 * Copyright (c) 2005-2026 The OPC Foundation, Inc. All rights reserved.
 *
 * OPC Foundation MIT License 1.00
 *
 * Permission is hereby granted, free of charge, to any person
 * obtaining a copy of this software and associated documentation
 * files (the "Software"), to deal in the Software without
 * restriction, including without limitation the rights to use,
 * copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 * OTHER DEALINGS IN THE SOFTWARE.
 *
 * The complete license agreement can be found here:
 * http://opcfoundation.org/License/MIT/1.00/
 * ======================================================================*/

using System;
using System.IO;
using System.Reflection;
#if NET8_0_OR_GREATER
using System.Runtime.InteropServices;
using System.Runtime.Loader;
#endif
using Opc.Ua.OpenUsd.Client;

namespace IntentViewerClient
{
    internal static class UsdViewHostLoader
    {
        public static bool TryLoad(out IUsdViewHost? host, out string reason)
        {
            host = null;
#if !NET8_0_OR_GREATER
            reason = "Rendering requires a .NET 8 or later target.";
            return false;
#else
            Assembly assembly;
            try
            {
                assembly = LoadViewerAssembly();
            }
            catch (Exception exception) when (
                exception is FileNotFoundException or FileLoadException or BadImageFormatException)
            {
                reason =
                    $"The optional '{ViewerAssemblyName}' assembly or its native payload was not found " +
                    "next to the sample. " +
                    "Run without --view for headless mode, or publish/run with the matching viewport package.";
                return false;
            }

            Type? type = assembly.GetType(ViewerTypeName, throwOnError: false);
            if (type is null)
            {
                reason = $"'{ViewerAssemblyName}' does not contain '{ViewerTypeName}'.";
                return false;
            }

            try
            {
                if (Activator.CreateInstance(type) is IUsdViewHost loaded)
                {
                    host = loaded;
                    reason = string.Empty;
                    return true;
                }
            }
            catch (Exception exception) when (exception is MissingMethodException or TargetInvocationException)
            {
                reason = $"The viewport could not be created: {exception.Message}";
                return false;
            }

            reason = $"'{ViewerTypeName}' does not implement IUsdViewHost.";
            return false;
#endif
        }

#if NET8_0_OR_GREATER
        private static Assembly LoadViewerAssembly()
        {
            string path = Path.Combine(AppContext.BaseDirectory, ViewerAssemblyName + ".dll");
            if (!File.Exists(path))
            {
                throw new FileNotFoundException("The optional viewport assembly is not installed.", path);
            }

            var resolver = new AssemblyDependencyResolver(path);
            AssemblyLoadContext.Default.Resolving += (context, name) =>
            {
                string? resolved = resolver.ResolveAssemblyToPath(name);
                if (resolved is null || !File.Exists(resolved))
                {
                    resolved = Path.Combine(AppContext.BaseDirectory, name.Name + ".dll");
                    if (!File.Exists(resolved))
                    {
                        return null;
                    }
                }
                return context.LoadFromAssemblyPath(resolved);
            };
            AssemblyLoadContext.Default.ResolvingUnmanagedDll += (_, unmanaged) =>
            {
                string? resolved = resolver.ResolveUnmanagedDllToPath(unmanaged);
                return resolved is not null && File.Exists(resolved) ? NativeLibrary.Load(resolved) : IntPtr.Zero;
            };
            return AssemblyLoadContext.Default.LoadFromAssemblyPath(path);
        }
#endif

#if NET8_0_OR_GREATER
        private const string ViewerAssemblyName = "Opc.Ua.OpenUsd.Connector.Viewer";
        private const string ViewerTypeName = "Opc.Ua.OpenUsd.Connector.Viewer.OpenUsdViewHost";
#endif
    }
}