[v3 windows] Add WndProcInterceptor for custom message processing

v3/V3 Changes.md

@@ -202,3 +202,17 @@ On Windows, if the `BackgroundType` is set to `BackgroundTypeTranslucent`, the t
 - `Tabbed` - The window will use the tabbed effect
 
 
+## Windows Application Options
+
+### WndProcInterceptor
+
+If this is set, the WndProc will be intercepted and the function will be called. This allows you to handle Windows 
+messages directly. The function should have the following signature:
+
+```go
+func(hwnd uintptr, msg uint32, wParam, lParam uintptr) (returnValue uintptr, shouldReturn)
+```
+
+The `shouldReturn` value should be set to `true` if the returnValue should be returned by the main wndProc method. 
+If it is set to `false`, the return value will be ignored and the message will continue to be processed by the main 
+wndProc method.

v3/pkg/application/application_windows.go

@@ -128,6 +128,15 @@ func (m *windowsApp) wndProc(hwnd w32.HWND, msg uint32, wParam, lParam uintptr)
 		m.invokeCallback(wParam, lParam)
 		return 0
 	}
+
+	// If the WndProcInterceptor is set in options, pass the message on
+	if m.parent.options.Windows.WndProcInterceptor != nil {
+		returnValue, shouldReturn := m.parent.options.Windows.WndProcInterceptor(hwnd, msg, wParam, lParam)
+		if shouldReturn {
+			return returnValue
+		}
+	}
+
 	switch msg {
 	case w32.WM_SETTINGCHANGE:
 		settingChanged := w32.UTF16PtrToString((*uint16)(unsafe.Pointer(lParam)))

v3/pkg/application/options_application.go

@@ -12,6 +12,7 @@ type Options struct {
 	Description string
 	Icon        []byte
 	Mac         MacOptions
+	Windows     WindowsApplicationOptions
 	Bind        []any
 	Logger      struct {
 		Silent        bool

v3/pkg/application/options_win.go

@@ -1,5 +1,13 @@
 package application
 
+type WindowsApplicationOptions struct {
+	// WndProcInterceptor is a function that will be called for every message sent in the application.
+	// Use this to hook into the main message loop. This is useful for handling custom window messages.
+	// If `shouldReturn` is `true` then `returnCode` will be returned by the main message loop.
+	// If `shouldReturn` is `false` then returnCode will be ignored and the message will be processed by the main message loop.
+	WndProcInterceptor func(hwnd uintptr, msg uint32, wParam, lParam uintptr) (returnCode uintptr, shouldReturn bool)
+}
+
 type BackdropType int32
 
 const (