app: [Windows] avoid default IME composition window

Mark WM_IME_STARTCOMPOSITION as handled after positioning the IME
composition and candidate windows.

Passing the message on to DefWindowProc can let Windows create its default
composition window, which shows the first composing character below Gio's
caret.

Fixes: https://todo.sr.ht/~eliasnaur/gio/687
Signed-off-by: qiannian <qianniancn@gmail.com>

app/os_windows.go

@@ -412,6 +412,7 @@ func windowProc(hwnd syscall.Handle, msg uint32, wParam, lParam uintptr) uintptr
 		icaret := image.Pt(int(caret.X+.5), int(caret.Y+.5))
 		windows.ImmSetCompositionWindow(imc, icaret.X, icaret.Y)
 		windows.ImmSetCandidateWindow(imc, icaret.X, icaret.Y)
+		return windows.TRUE
 	case windows.WM_IME_COMPOSITION:
 		imc := windows.ImmGetContext(w.hwnd)
 		if imc == 0 {

io/input/pointer.go

@@ -760,6 +760,8 @@ func (q *pointerQueue) Push(handlers map[event.Tag]*handler, state pointerState,
 		if p.pressed {
 			p, evts = q.deliverDragEvent(handlers, p, evts)
 		}
+	case pointer.Leave:
+		p, evts, state.cursor, _ = q.deliverEnterLeaveEvents(handlers, state.cursor, p, evts, e)
 	case pointer.Release:
 		evts = q.deliverEvent(handlers, p, evts, e)
 		p.pressed = false
@@ -823,7 +825,7 @@ func (q *pointerQueue) deliverEvent(handlers map[event.Tag]*handler, p pointerIn
 func (q *pointerQueue) deliverEnterLeaveEvents(handlers map[event.Tag]*handler, cursor pointer.Cursor, p pointerInfo, evts []taggedEvent, e pointer.Event) (pointerInfo, []taggedEvent, pointer.Cursor, bool) {
 	changed := false
 	var hits []event.Tag
-	if e.Source != pointer.Mouse && !p.pressed && e.Kind != pointer.Press {
+	if e.Kind == pointer.Leave || e.Source != pointer.Mouse && !p.pressed && e.Kind != pointer.Press {
 		// Consider non-mouse pointers leaving when they're released.
 	} else {
 		var transSrc *pointerFilter

io/input/pointer_test.go

@@ -255,6 +255,45 @@ func TestPointerMove(t *testing.T) {
 	assertEventPointerTypeSequence(t, events(&r, -1, filter(handler2)), pointer.Enter, pointer.Move, pointer.Leave, pointer.Cancel)
 }
 
+func TestPointerLeave(t *testing.T) {
+	handler := new(int)
+	var ops op.Ops
+
+	filter := pointer.Filter{
+		Target: handler,
+		Kinds:  pointer.Move | pointer.Enter | pointer.Leave | pointer.Cancel,
+	}
+	defer clip.Rect(image.Rect(0, 0, 100, 100)).Push(&ops).Pop()
+	event.Op(&ops, handler)
+
+	var r Router
+	events(&r, -1, filter)
+	r.Frame(&ops)
+	r.Queue(
+		pointer.Event{
+			Kind:      pointer.Move,
+			Source:    pointer.Mouse,
+			PointerID: 1,
+			Position:  f32.Pt(50, 50),
+		},
+		pointer.Event{
+			Kind:      pointer.Leave,
+			Source:    pointer.Mouse,
+			PointerID: 1,
+			Position:  f32.Pt(50, 50),
+		},
+	)
+	assertEventPointerTypeSequence(t, events(&r, -1, filter), pointer.Enter, pointer.Move, pointer.Leave)
+
+	r.Queue(pointer.Event{
+		Kind:      pointer.Move,
+		Source:    pointer.Mouse,
+		PointerID: 1,
+		Position:  f32.Pt(50, 50),
+	})
+	assertEventPointerTypeSequence(t, events(&r, -1, filter), pointer.Enter, pointer.Move)
+}
+
 func TestPointerTypes(t *testing.T) {
 	handler := new(int)
 	var ops op.Ops