Workaround for AL interop on Linux

[sk-zk]

This fix makes ALSoundOut work on both Linux and Windows.

Admittedly, it's not an ideal solution, but since the path for DllImport has to be constant, I couldn't really find a better way to do it.

[filoe]

Thanks for contributing.
Maybe we could add support for MacOS as well?

[sk-zk]

Probably. I don't know anything about Mac though so someone else is going to have to check that

[filoe]

Tried to look it up here https://github.com/opentk/opentk/blob/master/src/OpenAL/OpenToolkit.OpenAL/OpenALLibraryNameContainer.cs

Maybe we could load it dynamically anyways. I've already did something like that for xaudio and seems like opentk is doing something similar for all openal apis.

[mnadareski]

I had to end up modifying this slightly so that it worked, also putting it after the configuration PropertyGroups:

  <PropertyGroup Condition=" '$(OS)' == 'Windows_NT' ">
    <DefineConstants>$(DefineConstants);WINDOWS</DefineConstants>
  </PropertyGroup>

[Silverdimond]

I think a more viable solution that wouldn't require for it to be built for one or other platform would be following the microsoft example on cross platform P/Invoke
https://learn.microsoft.com/en-us/dotnet/standard/native-interop/cross-platform
I am not sure where to put the NativeLibrary.SetDllImportResolver instruction but it does seem to work if i put it in the constructor for ALSoundOut never mind you can only set it once which complicates things further.

//ALSoundOut line 89
public ALSoundOut(int latency, ThreadPriority playbackThreadPriority, SynchronizationContext eventSyncContext)
{
   if (latency <= 0)
     throw new ArgumentOutOfRangeException("latency");
   _latency = latency;
   _playbackPriority = playbackThreadPriority;
   _syncContext = eventSyncContext;
   if(!ResolverIsSet)
   {
      ResolverIsSet = true;
      NativeLibrary.SetDllImportResolver(Assembly.GetExecutingAssembly(), ALInteropsNativeMethods.DllImportResolver);
   }
   if (!ALInteropsNativeMethods.IsSupported())
   {
       throw new PlatformNotSupportedException("openAL is not supported by the current platform. Consider installing openAL on the current platform.");
   }
}
/// <summary>
/// Has ALSoundOut been called previously, if so skip setting the DLL import resolver
/// </summary>
 private static bool ResolverIsSet = false;
        
 //rename ALInterops to ALInteropsNativeMethods https://learn.microsoft.com/en-us/dotnet/fundamentals/code-analysis/quality-rules/ca1060
internal static class ALInteropsNativeMethods 
{
  private const string libLocation = "libopenal";
  public static IntPtr DllImportResolver(string libraryName, Assembly assembly, DllImportSearchPath? searchPath)
  {
     if (libraryName == "libopenal")
     {
         if (OperatingSystem.IsWindows())
         {
             return NativeLibrary.Load("openal32.dll", assembly, searchPath);
         }
      }
     return IntPtr.Zero;
 }

I've just realised that OperatingSystem.IsWindows() might require net6, you could probably just change it over to a check for Environment.OSVersion or better yet RuntimeInformation.IsOSPlatform(OSPlatform.Windows)