io/router: account for parent clip areas when scrolling focus into view

Fixes: https://todo.sr.ht/~eliasnaur/gio/389
Signed-off-by: Elias Naur <mail@eliasnaur.com>

io/router/key_test.go

@@ -274,6 +274,7 @@ func TestFocusScroll(t *testing.T) {
 	r := new(Router)
 	h := new(int)
 
+	parent := clip.Rect(image.Rect(1, 1, 14, 39)).Push(ops)
 	cl := clip.Rect(image.Rect(10, -20, 20, 30)).Push(ops)
 	key.InputOp{Tag: h}.Add(ops)
 	pointer.InputOp{
@@ -282,12 +283,13 @@ func TestFocusScroll(t *testing.T) {
 		ScrollBounds: image.Rect(-100, -100, 100, 100),
 	}.Add(ops)
 	cl.Pop()
+	parent.Pop()
 	r.Frame(ops)
 
 	r.MoveFocus(FocusLeft)
 	r.RevealFocus(image.Rect(0, 0, 15, 40))
 	evts := r.Events(h)
-	assertScrollEvent(t, evts[len(evts)-1], f32.Pt(5, -10))
+	assertScrollEvent(t, evts[len(evts)-1], f32.Pt(6, -9))
 }
 
 func TestFocusClick(t *testing.T) {

io/router/pointer.go

@@ -845,6 +845,18 @@ func (q *pointerQueue) deliverTransferCancelEvent(p *pointerInfo, events *handle
 	p.dataTarget = nil
 }
 
+// ClipFor clips r to the parents of area.
+func (q *pointerQueue) ClipFor(area int, r image.Rectangle) image.Rectangle {
+	a := &q.areas[area]
+	parent := a.parent
+	for parent != -1 {
+		a := &q.areas[parent]
+		r = r.Intersect(a.bounds())
+		parent = a.parent
+	}
+	return r
+}
+
 func searchTag(tags []event.Tag, tag event.Tag) (int, bool) {
 	for i, t := range tags {
 		if t == tag {

io/router/router.go

@@ -161,6 +161,8 @@ func (q *Router) RevealFocus(viewport image.Rectangle) {
 		return
 	}
 	bounds := q.key.queue.BoundsFor(focus)
+	area := q.key.queue.AreaFor(focus)
+	viewport = q.pointer.queue.ClipFor(area, viewport)
 
 	topleft := bounds.Min.Sub(viewport.Min)
 	topleft = max(topleft, bounds.Max.Sub(viewport.Max))