feat: add RNG setter

DirectMusic/Native.cs

@@ -40,6 +40,9 @@ internal static class Native
 		[UnmanagedFunctionPointer(CallingConvention.Cdecl)]
 		public delegate void DmLogHandler(IntPtr ctx, LogLevel lvl, string message);
 
+		[UnmanagedFunctionPointer(CallingConvention.Cdecl)]
+		public delegate uint DmRng(IntPtr ctx);
+
 		private const string DllName = "dmusic";
 
 		[DllImport(DllName)]
@@ -100,6 +103,9 @@ public static extern DmResult DmPerformance_playTransition(IntPtr slf, IntPtr sg
 		[DllImport(DllName)]
 		public static extern DmResult DmPerformance_renderPcm(IntPtr slf, float[] buf, ulong len, DmRenderOptions opts);
 
+		[DllImport(DllName)]
+		public static extern void Dm_setRandomNumberGenerator(DmRng rng, IntPtr ctx);
+
 		public class Structs
 		{
 		}

DirectMusic/RandomNumberGenerator.cs

@@ -0,0 +1,37 @@
+using System;
+using System.Runtime.InteropServices;
+using DirectMusic.Util;
+
+namespace DirectMusic
+{
+    public class RandomNumberGenerator
+    {
+        private static GCHandle? _handler;
+        private static readonly Native.DmRng NativeHandler = _nativeCallbackHandler;
+
+        /// <summary>
+        /// 
+        /// </summary>
+        public delegate int Callback();
+
+        /// <summary>
+        /// 
+        /// </summary>
+        public static void Set(Callback cb)
+        {
+            var handler = GCHandle.Alloc(cb);
+            Native.Dm_setRandomNumberGenerator(NativeHandler, GCHandle.ToIntPtr(handler));
+
+            _handler?.Free();
+            _handler = handler;
+        }
+
+        [MonoPInvokeCallback]
+        private static uint _nativeCallbackHandler(IntPtr ctx)
+        {
+            var gcHandle = GCHandle.FromIntPtr(ctx);
+            var cb = (Callback)gcHandle.Target;
+            return (uint) (cb() % uint.MaxValue);
+        }
+    }
+}