Reworked library loading so that the native DLL and its functions are now loaded dynamically using native LoadLibrary/GetProcAddress calls and can be freed again with FreeLibrary. This allows the library to be unloaded while in the Unity Editor, making iteration on native code easier, and it's a first step on the way to loading multiple Quake instances simultaneously.

Assets/Scripts/SystemLibrary.cs

@@ -0,0 +1,30 @@
+using System;
+using System.IO;
+using System.Runtime.InteropServices;
+
+public static class SystemLibrary
+{
+#if UNITY_STANDALONE_WIN
+    [DllImport("kernel32", EntryPoint = "LoadLibrary", SetLastError = true, CharSet = CharSet.Unicode)]
+    private static extern IntPtr LoadLibraryNative(string lpFileName);
+
+    [DllImport("kernel32", SetLastError = true, CharSet = CharSet.Unicode)]
+    [return: MarshalAs(UnmanagedType.Bool)]
+    private static extern bool SetDllDirectory(string lpPathName);
+
+    public static IntPtr LoadLibrary(string lpFileName)
+    {
+        string lpPathName = Path.GetDirectoryName(lpFileName);
+        lpFileName = Path.GetFileName(lpFileName);
+        SetDllDirectory(lpPathName.Replace('/', '\\'));
+        return LoadLibraryNative(lpFileName);
+    }
+
+    [DllImport("kernel32", SetLastError = true)]
+    [return: MarshalAs(UnmanagedType.Bool)]
+    public static extern bool FreeLibrary(IntPtr hModule);
+
+    [DllImport("kernel32")]
+    public static extern IntPtr GetProcAddress(IntPtr hModule, string procedureName);
+#endif
+}

Assets/Scripts/SystemLibrary.cs.meta

@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: d583e6fe28a9299438ec95a379db0527
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Assets/Scripts/UniQuake.cs

@@ -1,12 +1,24 @@
 using System;
+using System.IO;
 using System.Runtime.InteropServices;
 using UnityEngine;
 
 public class UniQuake: MonoBehaviour
-{
-    private const string DllName = "uniquake.dll";
+{
+#if UNITY_EDITOR
+    private const string DllPath = "Plugins/windows/x86_64/uniquake.dll";
+#elif UNITY_STANDALONE_WIN
+    #if UNITY_64
+    private const string DllPath = "Plugins/x86_64/uniquake.dll";
+    #else
+    private const string DllPath = "Plugins/x86/uniquake.dll";
+    #endif
+#endif
+
     private const int MemSize = 0x4000000;  // 64 MB of heap space
 
+    private IntPtr libraryHandle;
+
     private QuakeParms quakeParms;
     private SysCalls sysCalls;
     private ModCalls modCalls;
@@ -20,7 +32,12 @@ public class UniQuake: MonoBehaviour
     public double CurrentTime => Time.timeAsDouble - startTime;
 
     void Start()
-    {
+    {
+        sysCalls = new SysCalls(this);
+        modCalls = new ModCalls(this);
+
+        LoadLibrary();
+
         string[] arguments = 
         {
             "",
@@ -38,9 +55,6 @@ public class UniQuake: MonoBehaviour
         quakeParms.SetArguments(arguments);
         quakeParms.AllocateMemory(MemSize);
 
-        sysCalls = new SysCalls(this);
-        modCalls = new ModCalls(this);
-
         startTime = Time.timeAsDouble;
 
         try
@@ -106,16 +120,55 @@ public class UniQuake: MonoBehaviour
             quakeParms.Destroy();
             quakeParms = null;
         }
+
+        FreeLibrary();
     }
 
-    [DllImport(DllName, CallingConvention = CallingConvention.Cdecl)]
-    private static extern void UniQuake_Init(QuakeParms parms, IntPtr sysCalls, IntPtr modCalls);
+    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
+    private delegate void UniQuake_InitFunc(QuakeParms parms, IntPtr sysCalls, IntPtr modCalls);
+    private UniQuake_InitFunc UniQuake_Init;
+
+    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
+    private delegate void UniQuake_UpdateFunc(float deltaTime);
+    private UniQuake_UpdateFunc UniQuake_Update;
+
+    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
+    private delegate void UniQuake_ShutdownFunc();
+    private UniQuake_ShutdownFunc UniQuake_Shutdown;
 
-    [DllImport(DllName, CallingConvention = CallingConvention.Cdecl)]
-    private static extern void UniQuake_Update(float deltaTime);
+    private void LoadLibrary()
+    {
+        string dllFile = Path.Combine(Application.dataPath, DllPath);
+        libraryHandle = SystemLibrary.LoadLibrary(dllFile);
+        if (libraryHandle == IntPtr.Zero)
+        {
+            throw new DllNotFoundException($"Failed to load UniQuake library from path: {dllFile}, last error = {Marshal.GetLastWin32Error()}");
+        }
+
+        UniQuake_Init = LoadLibraryFunction<UniQuake_InitFunc>("UniQuake_Init");
+        UniQuake_Update = LoadLibraryFunction<UniQuake_UpdateFunc>("UniQuake_Update");
+        UniQuake_Shutdown = LoadLibraryFunction<UniQuake_ShutdownFunc>("UniQuake_Shutdown");
+    }
 
-    [DllImport(DllName, CallingConvention = CallingConvention.Cdecl)]
-    private static extern void UniQuake_Shutdown();
+    private TDelegate LoadLibraryFunction<TDelegate>(string name)
+    {
+        IntPtr procAddress = SystemLibrary.GetProcAddress(libraryHandle, name);
+        if (procAddress == IntPtr.Zero)
+        {
+            throw new DllNotFoundException($"Could not find library function: {name}");
+        }
+
+        return Marshal.GetDelegateForFunctionPointer<TDelegate>(procAddress);
+    }
+
+    private void FreeLibrary()
+    {
+        if (libraryHandle != IntPtr.Zero)
+        {
+            SystemLibrary.FreeLibrary(libraryHandle);
+            libraryHandle = IntPtr.Zero;
+        }
+    }
 }
 
 public class QuakeException: Exception