app: support changing Window options at runtime

A Window can now be requested to change its options after
it has been started via its Option method.

All options are supported on macOS, Windows and X11.
On Wayland, only the Size and Title options can be changed
at runtime.

Signed-off-by: pierre <pierre.curto@gmail.com>

app/internal/wm/os_windows.go

@@ -66,6 +66,7 @@ type window struct {
 const (
 	_WM_REDRAW = windows.WM_USER + iota
 	_WM_CURSOR
+	_WM_OPTION
 )
 
 type gpuAPI struct {
@@ -317,6 +318,8 @@ func windowProc(hwnd syscall.Handle, msg uint32, wParam, lParam uintptr) uintptr
 			windows.SetCursor(w.cursor)
 			return windows.TRUE
 		}
+	case _WM_OPTION:
+		w.setOptions()
 	}
 
 	return windows.DefWindowProc(hwnd, msg, wParam, lParam)
@@ -520,6 +523,18 @@ func (w *window) readClipboard() error {
 }
 
 func (w *window) Option(opts *Options) {
+	w.mu.Lock()
+	w.opts = opts
+	w.mu.Unlock()
+	if err := windows.PostMessage(w.hwnd, _WM_OPTION, 0, 0); err != nil {
+		panic(err)
+	}
+}
+
+func (w *window) setOptions() {
+	w.mu.Lock()
+	opts := w.opts
+	w.mu.Unlock()
 	if o := opts.Size; o != nil {
 		dpi := windows.GetSystemDPI()
 		cfg := configForDPI(dpi)