Added Window.SetTitle(). Also oops, forgot to mark the window as created.

main.go

@@ -16,7 +16,10 @@ mainloop:
 		case <-w.Closing:
 			break mainloop
 		case <-b.Clicked:
-			println("clicked")
+			err := w.SetTitle("Button Clicked")
+			if err != nil {
+				panic(err)
+			}
 		}
 	}
 	w.Close()

sysdata.go

@@ -25,6 +25,9 @@ func (c *cSysData) show() error {
 func (c *cSysData) hide() error {
 	panic(runtime.GOOS + " sysData does not define hide()")
 }
+func (c *cSysData) setText(text string) error {
+	panic(runtime.GOOS + " sysData does not define setText()")
+}
 
 const (
 	c_window = iota

sysdata_windows.go

@@ -143,3 +143,21 @@ func (s *sysData) hide() (err error) {
 	<-ret
 	return nil
 }
+
+func (s *sysData) setText(text string) error {
+	ret := make(chan uiret)
+	defer close(ret)
+	uitask <- &uimsg{
+		call:		_setWindowText,
+		p:		[]uintptr{
+			uintptr(s.hwnd),
+			uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr(text))),
+		},
+		ret:		ret,
+	}
+	r := <-ret
+	if r.ret == 0 {		// failure
+		return r.err
+	}
+	return nil
+}

todo.md

@@ -1,6 +1,7 @@
 so I don't forget:
 - Window.SizeToFit() or WIndow.OptimalSize() (use: `Window.SetSize(Window.OptimalSize())`) for sizing a window to the control's interest
 - Control.Show()/Control.Hide()
+- Control.SetText()
 
 super ultra important things:
 - the windows build appears to be unstable:

window.go

@@ -56,7 +56,7 @@ func (w *Window) SetTitle(title string) (err error) {
 	defer w.lock.Unlock()
 
 	if w.created {
-		panic("TODO")
+		return w.sysData.setText(title)
 	}
 	w.initTitle = title
 	return nil
@@ -93,6 +93,7 @@ func (w *Window) Open() (err error) {
 				return err
 			}
 		}
+		w.created = true
 	}
 	return w.sysData.show()
 }

windows_windows.go

@@ -170,6 +170,7 @@ var (
 	_getClientRect = user32.NewProc("GetClientRect")
 	_enumChildWindows = user32.NewProc("EnumChildWindows")
 	_setWindowPos = user32.NewProc("SetWindowPos")
+	_setWindowText = user32.NewProc("SetWindowTextW")
 	_showWindow = user32.NewProc("ShowWindow")
 )