Added EventWatcher

src/KappaDuck.Quack/Events/EventManager.cs

@@ -179,6 +179,19 @@ public static bool Wait(out Event e, TimeSpan? timeout = null)
         return Native.SDL_WaitEventTimeout(out e, (int)timeout.Value.TotalMilliseconds);
     }
 
+    /// <summary>
+    /// Creates an event watcher that invokes the specified callback function whenever an event is added to the event queue.
+    /// </summary>
+    /// <param name="callback">The callback function to be invoked when an event is added.</param>
+    public static EventWatcher Watch(Action<Event> callback)
+    {
+        return new EventWatcher((_, ref e) =>
+        {
+            callback(e);
+            return true;
+        });
+    }
+
     private static void ThrowIfInvalidRange(EventType min, EventType? max)
     {
         if (max is null)

src/KappaDuck.Quack/Events/EventWatcher.cs

@@ -0,0 +1,24 @@
+// Copyright (c) KappaDuck. All rights reserved.
+// The source code is licensed under MIT License.
+
+namespace KappaDuck.Quack.Events;
+
+/// <summary>
+/// Represents an event watcher to monitor new events added to the event queue.
+/// </summary>
+/// <remarks>
+/// You can dispose the watcher to stop monitoring events.
+/// </remarks>
+public sealed class EventWatcher : IDisposable
+{
+    private readonly Native.EventFilter _callback;
+
+    internal EventWatcher(Native.EventFilter callback)
+    {
+        _callback = callback;
+        Native.SDL_AddEventWatch(_callback);
+    }
+
+    /// <inheritdoc/>
+    public void Dispose() => Native.SDL_RemoveEventWatch(_callback);
+}

src/KappaDuck.Quack/Interop/SDL/Native.Events.cs

@@ -7,6 +7,11 @@ namespace KappaDuck.Quack.Interop.SDL;
 
 internal static partial class Native
 {
+    [LibraryImport(SDL), UnmanagedCallConv(CallConvs = [typeof(CallConvCdecl)])]
+    [DefaultDllImportSearchPaths(DllImportSearchPath.SafeDirectories)]
+    [return: MarshalAs(UnmanagedType.U1)]
+    internal static partial bool SDL_AddEventWatch(EventFilter callback, nint data = default);
+
     [LibraryImport(SDL), UnmanagedCallConv(CallConvs = [typeof(CallConvCdecl)])]
     [DefaultDllImportSearchPaths(DllImportSearchPath.SafeDirectories)]
     [return: MarshalAs(UnmanagedType.U1)]
@@ -48,6 +53,11 @@ internal static partial class Native
     [return: MarshalAs(UnmanagedType.U1)]
     internal static partial bool SDL_PushEvent(ref Event e);
 
+    [LibraryImport(SDL), UnmanagedCallConv(CallConvs = [typeof(CallConvCdecl)])]
+    [DefaultDllImportSearchPaths(DllImportSearchPath.SafeDirectories)]
+    [return: MarshalAs(UnmanagedType.U1)]
+    internal static partial bool SDL_RemoveEventWatch(EventFilter callback, nint data = default);
+
     [LibraryImport(SDL), UnmanagedCallConv(CallConvs = [typeof(CallConvCdecl)])]
     [DefaultDllImportSearchPaths(DllImportSearchPath.SafeDirectories)]
     internal static partial void SDL_SetEventEnabled(EventType type, [MarshalAs(UnmanagedType.U1)] bool enabled);
@@ -61,4 +71,8 @@ internal static partial class Native
     [DefaultDllImportSearchPaths(DllImportSearchPath.SafeDirectories)]
     [return: MarshalAs(UnmanagedType.U1)]
     internal static partial bool SDL_WaitEventTimeout(out Event e, int timeout);
+
+    [UnmanagedFunctionPointer(CallingConvention.Cdecl)]
+    [return: MarshalAs(UnmanagedType.U1)]
+    internal delegate bool EventFilter(nint userdata, ref Event e);
 }