io/input: merge per-handler state

We're about to need per-handler state related to neither pointer nor
key input. This change merges the pointer and key handler state into one
state struct, tracked in the Router.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

io/input/key.go

@@ -26,7 +26,6 @@ type TextInputState uint8
 type keyQueue struct {
 	order    []event.Tag
 	dirOrder []dirFocusEntry
-	handlers map[event.Tag]*keyHandler
 	hint     key.InputHint
 }
 
@@ -43,14 +42,21 @@ type keyHandler struct {
 	visible bool
 	// reset tracks whether the handler has seen a
 	// focus reset.
-	reset     bool
+	reset        bool
+	hint         key.InputHint
+	orderPlusOne int
+	dirOrder     int
+	// filter are the key filters accumulated in the previous frame,
+	// used for routing events in the current frame.
+	filter keyFilter
+	// nextFilter is the filter accumulator for the current frame.
+	nextFilter keyFilter
+	trans      f32.Affine2D
+}
+
+type keyFilter struct {
 	focusable bool
-	active    bool
-	hint      key.InputHint
-	order     int
-	dirOrder  int
 	filters   []key.Filter
-	trans     f32.Affine2D
 }
 
 type dirFocusEntry struct {
@@ -66,9 +72,8 @@ const (
 	TextInputOpen
 )
 
-func (q *keyQueue) inputHint(op key.InputHintOp) {
-	h := q.handlerFor(op.Tag)
-	h.hint = op.Hint
+func (k *keyHandler) inputHint(hint key.InputHint) {
+	k.hint = hint
 }
 
 // InputState returns the input state and returns a state
@@ -81,52 +86,46 @@ func (s keyState) InputState() (keyState, TextInputState) {
 
 // InputHint returns the input hint from the focused handler and whether it was
 // changed since the last call.
-func (q *keyQueue) InputHint(state keyState) (key.InputHint, bool) {
-	focused, ok := q.handlers[state.focus]
+func (q *keyQueue) InputHint(handlers map[event.Tag]*handler, state keyState) (key.InputHint, bool) {
+	focused, ok := handlers[state.focus]
 	if !ok {
 		return q.hint, false
 	}
 	old := q.hint
-	q.hint = focused.hint
+	q.hint = focused.key.hint
 	return q.hint, old != q.hint
 }
 
+func (k *keyHandler) Reset() {
+	k.filter, k.nextFilter = k.nextFilter, k.filter
+	k.nextFilter = keyFilter{}
+	k.visible = false
+	k.orderPlusOne = 0
+	k.hint = key.HintAny
+}
+
 func (q *keyQueue) Reset() {
-	for _, h := range q.handlers {
-		h.order = -1
-		h.hint = key.HintAny
-	}
 	q.order = q.order[:0]
 	q.dirOrder = q.dirOrder[:0]
 }
 
-func (q *keyQueue) ResetEvent(k event.Tag) (event.Event, bool) {
-	h, ok := q.handlers[k]
-	if !ok || h.reset {
+func (k *keyHandler) ResetEvent() (event.Event, bool) {
+	if k.reset {
 		return nil, false
 	}
-	h.reset = true
+	k.reset = true
 	return key.FocusEvent{Focus: false}, true
 }
 
-func (q *keyQueue) Frame(state keyState) keyState {
-	for k, h := range q.handlers {
-		if !h.visible || !h.focusable {
-			if state.focus == k {
-				// Remove focus from the handler that is no longer focusable.
-				state.focus = nil
-				state.state = TextInputClose
-			}
-			if !h.visible && !h.focusable {
-				delete(q.handlers, k)
-				continue
-			}
+func (q *keyQueue) Frame(handlers map[event.Tag]*handler, state keyState) keyState {
+	if state.focus != nil {
+		if h, ok := handlers[state.focus]; !ok || !h.key.isFocusable() {
+			// Remove focus from the handler that is no longer focusable.
+			state.focus = nil
+			state.state = TextInputClose
 		}
-		h.visible = false
-		h.focusable = false
-		h.active = false
 	}
-	q.updateFocusLayout()
+	q.updateFocusLayout(handlers)
 	return state
 }
 
@@ -137,7 +136,7 @@ func (q *keyQueue) Frame(state keyState) keyState {
 // containing it. Then, extend the handler bounds to a horizontal beam
 // and add to the row every handler whose center intersect it. Repeat
 // until no handlers remain.
-func (q *keyQueue) updateFocusLayout() {
+func (q *keyQueue) updateFocusLayout(handlers map[event.Tag]*handler) {
 	order := q.dirOrder
 	// Sort by ascending y position.
 	sort.SliceStable(order, func(i, j int) bool {
@@ -165,18 +164,18 @@ func (q *keyQueue) updateFocusLayout() {
 		row++
 	}
 	for i, o := range q.dirOrder {
-		q.handlers[o.tag].dirOrder = i
+		handlers[o.tag].key.dirOrder = i
 	}
 }
 
 // MoveFocus attempts to move the focus in the direction of dir.
-func (q *keyQueue) MoveFocus(state keyState, dir key.FocusDirection) (keyState, []taggedEvent) {
+func (q *keyQueue) MoveFocus(handlers map[event.Tag]*handler, state keyState, dir key.FocusDirection) (keyState, []taggedEvent) {
 	if len(q.dirOrder) == 0 {
 		return state, nil
 	}
 	order := 0
 	if state.focus != nil {
-		order = q.handlers[state.focus].dirOrder
+		order = handlers[state.focus].key.dirOrder
 	}
 	focus := q.dirOrder[order]
 	switch dir {
@@ -189,7 +188,7 @@ func (q *keyQueue) MoveFocus(state keyState, dir key.FocusDirection) (keyState,
 			order = -1
 		}
 		if state.focus != nil {
-			order = q.handlers[state.focus].order
+			order = handlers[state.focus].key.orderPlusOne - 1
 			if dir == key.FocusForward {
 				order++
 			} else {
@@ -197,7 +196,7 @@ func (q *keyQueue) MoveFocus(state keyState, dir key.FocusDirection) (keyState,
 			}
 		}
 		order = (order + len(q.order)) % len(q.order)
-		return q.Focus(state, q.order[order])
+		return q.Focus(handlers, state, q.order[order])
 	case key.FocusRight, key.FocusLeft:
 		next := order
 		if state.focus != nil {
@@ -209,7 +208,7 @@ func (q *keyQueue) MoveFocus(state keyState, dir key.FocusDirection) (keyState,
 		if 0 <= next && next < len(q.dirOrder) {
 			newFocus := q.dirOrder[next]
 			if newFocus.row == focus.row {
-				return q.Focus(state, newFocus.tag)
+				return q.Focus(handlers, state, newFocus.tag)
 			}
 		}
 	case key.FocusUp, key.FocusDown:
@@ -245,24 +244,24 @@ func (q *keyQueue) MoveFocus(state keyState, dir key.FocusDirection) (keyState,
 			order += delta
 		}
 		if closest != nil {
-			return q.Focus(state, closest)
+			return q.Focus(handlers, state, closest)
 		}
 	}
 	return state, nil
 }
 
-func (q *keyQueue) BoundsFor(t event.Tag) image.Rectangle {
-	order := q.handlers[t].dirOrder
+func (q *keyQueue) BoundsFor(k *keyHandler) image.Rectangle {
+	order := k.dirOrder
 	return q.dirOrder[order].bounds
 }
 
-func (q *keyQueue) AreaFor(t event.Tag) int {
-	order := q.handlers[t].dirOrder
+func (q *keyQueue) AreaFor(k *keyHandler) int {
+	order := k.dirOrder
 	return q.dirOrder[order].area
 }
 
-func (q *keyQueue) Accepts(t event.Tag, e key.Event) bool {
-	for _, f := range q.handlers[t].filters {
+func (k *keyHandler) Accepts(e key.Event) bool {
+	for _, f := range k.filter.filters {
 		if keyFilterMatch(f, e) {
 			return true
 		}
@@ -283,9 +282,9 @@ func keyFilterMatch(f key.Filter, e key.Event) bool {
 	return true
 }
 
-func (q *keyQueue) Focus(state keyState, focus event.Tag) (keyState, []taggedEvent) {
+func (q *keyQueue) Focus(handlers map[event.Tag]*handler, state keyState, focus event.Tag) (keyState, []taggedEvent) {
 	if focus != nil {
-		if _, exists := q.handlers[focus]; !exists {
+		if h, exists := handlers[focus]; !exists || !h.key.isFocusable() {
 			focus = nil
 		}
 	}
@@ -316,41 +315,26 @@ func (s keyState) softKeyboard(show bool) keyState {
 	return s
 }
 
-func (q *keyQueue) filter(tag event.Tag, f key.Filter) {
-	h := q.handlerFor(tag)
-	if !h.active {
-		h.active = true
-		h.filters = h.filters[:0]
-	}
-	h.filters = append(h.filters, f)
+func (k *keyHandler) Filter(f key.Filter) {
+	k.nextFilter.filters = append(k.nextFilter.filters, f)
 }
 
-func (q *keyQueue) focusable(tag event.Tag) {
-	h := q.handlerFor(tag)
-	h.focusable = true
+func (k *keyHandler) isFocusable() bool {
+	return k.filter.focusable && k.visible
 }
 
-func (q *keyQueue) handlerFor(tag event.Tag) *keyHandler {
-	h, ok := q.handlers[tag]
-	if !ok {
-		h = &keyHandler{order: -1}
-		if q.handlers == nil {
-			q.handlers = make(map[event.Tag]*keyHandler)
-		}
-		q.handlers[tag] = h
-	}
-	return h
+func (k *keyHandler) Focusable() {
+	k.nextFilter.focusable = true
 }
 
-func (q *keyQueue) inputOp(tag event.Tag, t f32.Affine2D, area int, bounds image.Rectangle) {
-	h := q.handlerFor(tag)
-	if h.order == -1 {
-		h.order = len(q.order)
+func (q *keyQueue) inputOp(tag event.Tag, state *keyHandler, t f32.Affine2D, area int, bounds image.Rectangle) {
+	state.visible = true
+	if state.orderPlusOne == 0 {
+		state.orderPlusOne = len(q.order) + 1
 		q.order = append(q.order, tag)
 		q.dirOrder = append(q.dirOrder, dirFocusEntry{tag: tag, area: area, bounds: bounds})
 	}
-	h.visible = true
-	h.trans = t
+	state.trans = t
 }
 
 func (q *keyQueue) setSelection(state keyState, req key.SelectionCmd) keyState {
@@ -362,10 +346,10 @@ func (q *keyQueue) setSelection(state keyState, req key.SelectionCmd) keyState {
 	return state
 }
 
-func (q *keyQueue) editorState(state keyState) EditorState {
+func (q *keyQueue) editorState(handlers map[event.Tag]*handler, state keyState) EditorState {
 	s := state.content
 	if f := state.focus; f != nil {
-		s.Selection.Transform = q.handlers[f].trans
+		s.Selection.Transform = handlers[f].key.trans
 	}
 	return s
 }

io/input/pointer.go

@@ -17,9 +17,8 @@ import (
 )
 
 type pointerQueue struct {
-	hitTree  []hitNode
-	areas    []areaNode
-	handlers map[event.Tag]*pointerHandler
+	hitTree []hitNode
+	areas   []areaNode
 
 	semantic struct {
 		idsAssigned bool
@@ -62,12 +61,22 @@ type pointerInfo struct {
 }
 
 type pointerHandler struct {
-	area int
+	// areaPlusOne is the index into the list of pointerQueue.areas, plus 1.
+	areaPlusOne int
 	// setup tracks whether the handler has received
 	// the pointer.Cancel event that resets its state.
-	setup  bool
-	active bool
-	types  pointer.Kind
+	setup bool
+	// filter is the combined filter of every filter the handler has
+	// asked for through event handling in the previous frame. It is
+	// used for routing events in the current frame.
+	filter pointerFilter
+	// prevFilter is the filter being built in the current frame.
+	nextFilter pointerFilter
+}
+
+// pointerFilter represents the union of a set of pointer filters.
+type pointerFilter struct {
+	kinds pointer.Kind
 	// min and max horizontal/vertical scroll
 	scrollRange image.Rectangle
 
@@ -228,37 +237,20 @@ func (c *pointerCollector) addHitNode(n hitNode) {
 }
 
 // newHandler returns the current handler or a new one for tag.
-func (c *pointerCollector) newHandler(tag event.Tag) *pointerHandler {
+func (c *pointerCollector) newHandler(tag event.Tag, state *pointerHandler) {
 	areaID := c.currentArea()
 	c.addHitNode(hitNode{
 		area: areaID,
 		tag:  tag,
 		pass: c.state.pass > 0,
 	})
-	h := c.q.handlerFor(tag)
-	h.area = areaID
-	return h
+	state.areaPlusOne = areaID + 1
 }
 
-func (q *pointerQueue) handlerFor(tag event.Tag) *pointerHandler {
-	h, ok := q.handlers[tag]
-	if !ok {
-		h = &pointerHandler{
-			area: -1,
-		}
-		if q.handlers == nil {
-			q.handlers = make(map[event.Tag]*pointerHandler)
-		}
-		q.handlers[tag] = h
-	}
-	if !h.active {
-		h.types = 0
-		h.scrollRange = image.Rectangle{}
-		h.sourceMimes = h.sourceMimes[:0]
-		h.targetMimes = h.targetMimes[:0]
-	}
-	h.active = true
-	return h
+func (s *pointerHandler) Reset() {
+	s.areaPlusOne = 0
+	s.filter = s.nextFilter
+	s.nextFilter = pointerFilter{}
 }
 
 func (c *pointerCollector) actionInputOp(act system.Action) {
@@ -288,25 +280,23 @@ func (q *pointerQueue) grab(state pointerState, req pointer.GrabCmd) (pointerSta
 	return state, evts
 }
 
-func (c *pointerCollector) inputOp(tag event.Tag) {
+func (c *pointerCollector) inputOp(tag event.Tag, state *pointerHandler) {
 	areaID := c.currentArea()
 	area := &c.q.areas[areaID]
 	area.semantic.content.tag = tag
-	c.newHandler(tag)
+	c.newHandler(tag, state)
 }
 
-func (q *pointerQueue) filterTag(tag event.Tag, f pointer.Filter) {
-	h := q.handlerFor(tag)
-	h.types = h.types | f.Kinds
-	h.scrollRange = h.scrollRange.Union(f.ScrollBounds)
+func (s *pointerHandler) Filter(tag event.Tag, f pointer.Filter) {
+	s.nextFilter.kinds = s.nextFilter.kinds | f.Kinds
+	s.nextFilter.scrollRange = s.nextFilter.scrollRange.Union(f.ScrollBounds)
 }
 
-func (q *pointerQueue) ResetEvent(tag event.Tag) (event.Event, bool) {
-	h, ok := q.handlers[tag]
-	if !ok || h.setup {
+func (s *pointerHandler) ResetEvent() (event.Event, bool) {
+	if s.setup {
 		return nil, false
 	}
-	h.setup = true
+	s.setup = true
 	return pointer.Event{Kind: pointer.Cancel}, true
 }
 
@@ -351,17 +341,15 @@ func (c *pointerCollector) cursor(cursor pointer.Cursor) {
 	area.cursor = cursor
 }
 
-func (q *pointerQueue) sourceFilter(tag event.Tag, f transfer.SourceFilter) {
-	h := q.handlerFor(tag)
-	h.sourceMimes = append(h.sourceMimes, f.Type)
+func (s *pointerHandler) SourceFilter(tag event.Tag, f transfer.SourceFilter) {
+	s.nextFilter.sourceMimes = append(s.nextFilter.sourceMimes, f.Type)
 }
 
-func (q *pointerQueue) targetFilter(tag event.Tag, f transfer.TargetFilter) {
-	h := q.handlerFor(tag)
-	h.targetMimes = append(h.targetMimes, f.Type)
+func (s *pointerHandler) TargetFilter(tag event.Tag, f transfer.TargetFilter) {
+	s.nextFilter.targetMimes = append(s.nextFilter.targetMimes, f.Type)
 }
 
-func (q *pointerQueue) offerData(state pointerState, req transfer.OfferCmd) (pointerState, []taggedEvent) {
+func (q *pointerQueue) offerData(handlers map[event.Tag]*handler, state pointerState, req transfer.OfferCmd) (pointerState, []taggedEvent) {
 	var evts []taggedEvent
 	for i, p := range state.pointers {
 		if p.dataSource != req.Tag {
@@ -376,13 +364,13 @@ func (q *pointerQueue) offerData(state pointerState, req transfer.OfferCmd) (poi
 			}})
 		}
 		state.pointers = append([]pointerInfo{}, state.pointers...)
-		state.pointers[i], evts = q.deliverTransferCancelEvent(p, evts)
+		state.pointers[i], evts = q.deliverTransferCancelEvent(handlers, p, evts)
 		break
 	}
 	return state, evts
 }
 
-func (c *pointerCollector) reset() {
+func (c *pointerCollector) Reset() {
 	c.q.reset()
 	c.resetState()
 	c.ensureRoot()
@@ -537,19 +525,6 @@ func (q *pointerQueue) hitTest(pos f32.Point, onNode func(*hitNode) bool) pointe
 	return cursor
 }
 
-func (q *pointerQueue) opHit(pos f32.Point) ([]event.Tag, pointer.Cursor) {
-	var hits []event.Tag
-	cursor := q.hitTest(pos, func(n *hitNode) bool {
-		if n.tag != nil {
-			if _, exists := q.handlers[n.tag]; exists {
-				hits = addHandler(hits, n.tag)
-			}
-		}
-		return true
-	})
-	return hits, cursor
-}
-
 func (q *pointerQueue) invTransform(areaIdx int, p f32.Point) f32.Point {
 	if areaIdx == -1 {
 		return p
@@ -574,10 +549,6 @@ func (q *pointerQueue) hit(areaIdx int, p f32.Point) (bool, pointer.Cursor) {
 }
 
 func (q *pointerQueue) reset() {
-	for _, h := range q.handlers {
-		// Reset handler.
-		h.area = -1
-	}
 	q.hitTree = q.hitTree[:0]
 	q.areas = q.areas[:0]
 	q.semantic.idsAssigned = false
@@ -597,20 +568,14 @@ func (q *pointerQueue) reset() {
 	}
 }
 
-func (q *pointerQueue) Frame(state pointerState) (pointerState, []taggedEvent) {
-	for k, h := range q.handlers {
-		if !h.active {
-			state = dropHandler(state, k)
-			delete(q.handlers, k)
-			continue
-		}
-		h.active = false
-		if h.area != -1 {
-			area := &q.areas[h.area]
-			if h.types&(pointer.Press|pointer.Release) != 0 {
+func (q *pointerQueue) Frame(handlers map[event.Tag]*handler, state pointerState) (pointerState, []taggedEvent) {
+	for _, h := range handlers {
+		if h.pointer.areaPlusOne != 0 {
+			area := &q.areas[h.pointer.areaPlusOne-1]
+			if h.pointer.filter.kinds&(pointer.Press|pointer.Release) != 0 {
 				area.semantic.content.gestures |= ClickGesture
 			}
-			if h.types&pointer.Scroll != 0 {
+			if h.pointer.filter.kinds&pointer.Scroll != 0 {
 				area.semantic.content.gestures |= ScrollGesture
 			}
 			area.semantic.valid = area.semantic.content.gestures != 0
@@ -619,7 +584,7 @@ func (q *pointerQueue) Frame(state pointerState) (pointerState, []taggedEvent) {
 	var evts []taggedEvent
 	for i, p := range state.pointers {
 		changed := false
-		p, evts, state.cursor, changed = q.deliverEnterLeaveEvents(state.cursor, p, evts, p.last)
+		p, evts, state.cursor, changed = q.deliverEnterLeaveEvents(handlers, state.cursor, p, evts, p.last)
 		if changed {
 			state.pointers = append([]pointerInfo{}, state.pointers...)
 			state.pointers[i] = p
@@ -664,7 +629,7 @@ func (s pointerState) pointerOf(e pointer.Event) (pointerState, int) {
 }
 
 // Deliver is like Push, but delivers an event to a particular area.
-func (q *pointerQueue) Deliver(areaIdx int, e pointer.Event) []taggedEvent {
+func (q *pointerQueue) Deliver(handlers map[event.Tag]*handler, areaIdx int, e pointer.Event) []taggedEvent {
 	var sx, sy = e.Scroll.X, e.Scroll.Y
 	idx := len(q.hitTree) - 1
 	// Locate first potential receiver.
@@ -679,23 +644,21 @@ func (q *pointerQueue) Deliver(areaIdx int, e pointer.Event) []taggedEvent {
 	for idx != -1 {
 		n := &q.hitTree[idx]
 		idx = n.next
-		if n.tag == nil {
-			continue
-		}
-		h := q.handlers[n.tag]
-		if h == nil || e.Kind&h.types == 0 {
+		h, ok := handlers[n.tag]
+		if !ok || e.Kind&h.pointer.filter.kinds == 0 {
 			continue
 		}
+		f := h.pointer.filter
 		e := e
 		if e.Kind == pointer.Scroll {
 			if sx == 0 && sy == 0 {
 				break
 			}
 			// Distribute the scroll to the handler based on its ScrollRange.
-			sx, e.Scroll.X = setScrollEvent(sx, h.scrollRange.Min.X, h.scrollRange.Max.X)
-			sy, e.Scroll.Y = setScrollEvent(sy, h.scrollRange.Min.Y, h.scrollRange.Max.Y)
+			sx, e.Scroll.X = setScrollEvent(sx, f.scrollRange.Min.X, f.scrollRange.Max.X)
+			sy, e.Scroll.Y = setScrollEvent(sy, f.scrollRange.Min.Y, f.scrollRange.Max.Y)
 		}
-		e.Position = q.invTransform(h.area, e.Position)
+		e.Position = q.invTransform(h.pointer.areaPlusOne-1, e.Position)
 		evts = append(evts, taggedEvent{tag: n.tag, event: e})
 		if e.Kind != pointer.Scroll {
 			break
@@ -717,10 +680,10 @@ func (q *pointerQueue) SemanticArea(areaIdx int) (semanticContent, int) {
 	return semanticContent{}, -1
 }
 
-func (q *pointerQueue) Push(state pointerState, e pointer.Event) (pointerState, []taggedEvent) {
+func (q *pointerQueue) Push(handlers map[event.Tag]*handler, state pointerState, e pointer.Event) (pointerState, []taggedEvent) {
 	var evts []taggedEvent
 	if e.Kind == pointer.Cancel {
-		for k := range q.handlers {
+		for k := range handlers {
 			evts = append(evts, taggedEvent{
 				event: pointer.Event{Kind: pointer.Cancel},
 				tag:   k,
@@ -734,26 +697,26 @@ func (q *pointerQueue) Push(state pointerState, e pointer.Event) (pointerState,
 
 	switch e.Kind {
 	case pointer.Press:
-		p, evts, state.cursor, _ = q.deliverEnterLeaveEvents(state.cursor, p, evts, e)
+		p, evts, state.cursor, _ = q.deliverEnterLeaveEvents(handlers, state.cursor, p, evts, e)
 		p.pressed = true
-		evts = q.deliverEvent(p, evts, e)
+		evts = q.deliverEvent(handlers, p, evts, e)
 	case pointer.Move:
 		if p.pressed {
 			e.Kind = pointer.Drag
 		}
-		p, evts, state.cursor, _ = q.deliverEnterLeaveEvents(state.cursor, p, evts, e)
-		evts = q.deliverEvent(p, evts, e)
+		p, evts, state.cursor, _ = q.deliverEnterLeaveEvents(handlers, state.cursor, p, evts, e)
+		evts = q.deliverEvent(handlers, p, evts, e)
 		if p.pressed {
-			p, evts = q.deliverDragEvent(p, evts)
+			p, evts = q.deliverDragEvent(handlers, p, evts)
 		}
 	case pointer.Release:
-		evts = q.deliverEvent(p, evts, e)
+		evts = q.deliverEvent(handlers, p, evts, e)
 		p.pressed = false
-		p, evts, state.cursor, _ = q.deliverEnterLeaveEvents(state.cursor, p, evts, e)
-		p, evts = q.deliverDropEvent(p, evts)
+		p, evts, state.cursor, _ = q.deliverEnterLeaveEvents(handlers, state.cursor, p, evts, e)
+		p, evts = q.deliverDropEvent(handlers, p, evts)
 	case pointer.Scroll:
-		p, evts, state.cursor, _ = q.deliverEnterLeaveEvents(state.cursor, p, evts, e)
-		evts = q.deliverEvent(p, evts, e)
+		p, evts, state.cursor, _ = q.deliverEnterLeaveEvents(handlers, state.cursor, p, evts, e)
+		evts = q.deliverEvent(handlers, p, evts, e)
 	default:
 		panic("unsupported pointer event type")
 	}
@@ -770,7 +733,7 @@ func (q *pointerQueue) Push(state pointerState, e pointer.Event) (pointerState,
 	return state, evts
 }
 
-func (q *pointerQueue) deliverEvent(p pointerInfo, evts []taggedEvent, e pointer.Event) []taggedEvent {
+func (q *pointerQueue) deliverEvent(handlers map[event.Tag]*handler, p pointerInfo, evts []taggedEvent, e pointer.Event) []taggedEvent {
 	foremost := true
 	if p.pressed && len(p.handlers) == 1 {
 		e.Priority = pointer.Grabbed
@@ -778,16 +741,20 @@ func (q *pointerQueue) deliverEvent(p pointerInfo, evts []taggedEvent, e pointer
 	}
 	var sx, sy = e.Scroll.X, e.Scroll.Y
 	for _, k := range p.handlers {
-		h := q.handlers[k]
+		h, ok := handlers[k]
+		if !ok {
+			continue
+		}
+		f := h.pointer.filter
 		if e.Kind == pointer.Scroll {
 			if sx == 0 && sy == 0 {
 				return evts
 			}
 			// Distribute the scroll to the handler based on its ScrollRange.
-			sx, e.Scroll.X = setScrollEvent(sx, h.scrollRange.Min.X, h.scrollRange.Max.X)
-			sy, e.Scroll.Y = setScrollEvent(sy, h.scrollRange.Min.Y, h.scrollRange.Max.Y)
+			sx, e.Scroll.X = setScrollEvent(sx, f.scrollRange.Min.X, f.scrollRange.Max.X)
+			sy, e.Scroll.Y = setScrollEvent(sy, f.scrollRange.Min.Y, f.scrollRange.Max.Y)
 		}
-		if e.Kind&h.types == 0 {
+		if e.Kind&f.kinds == 0 {
 			continue
 		}
 		e := e
@@ -795,38 +762,47 @@ func (q *pointerQueue) deliverEvent(p pointerInfo, evts []taggedEvent, e pointer
 			foremost = false
 			e.Priority = pointer.Foremost
 		}
-		e.Position = q.invTransform(h.area, e.Position)
+		e.Position = q.invTransform(h.pointer.areaPlusOne-1, e.Position)
 		evts = append(evts, taggedEvent{event: e, tag: k})
 	}
 	return evts
 }
 
-func (q *pointerQueue) deliverEnterLeaveEvents(cursor pointer.Cursor, p pointerInfo, evts []taggedEvent, e pointer.Event) (pointerInfo, []taggedEvent, pointer.Cursor, bool) {
+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 {
 		// Consider non-mouse pointers leaving when they're released.
 	} else {
-		hits, cursor = q.opHit(e.Position)
-		if p.pressed {
-			// Filter out non-participating handlers,
-			// except potential transfer targets when a transfer has been initiated.
-			var hitsHaveTarget bool
-			if p.dataSource != nil {
-				transferSource := q.handlers[p.dataSource]
-				for _, hit := range hits {
-					if _, ok := firstMimeMatch(transferSource, q.handlers[hit]); ok {
-						hitsHaveTarget = true
-						break
+		var transSrc *pointerHandler
+		if p.dataSource != nil {
+			transSrc = &handlers[p.dataSource].pointer
+		}
+		cursor = q.hitTest(e.Position, func(n *hitNode) bool {
+			h, ok := handlers[n.tag]
+			if !ok {
+				return true
+			}
+			add := true
+			if p.pressed {
+				add = false
+				// Filter out non-participating handlers,
+				// except potential transfer targets when a transfer has been initiated.
+				if _, found := searchTag(p.handlers, n.tag); found {
+					add = true
+				}
+				if transSrc != nil {
+					if _, ok := firstMimeMatch(transSrc, &h.pointer); ok {
+						add = true
 					}
 				}
 			}
-			for i := len(hits) - 1; i >= 0; i-- {
-				if _, found := searchTag(p.handlers, hits[i]); !found && !hitsHaveTarget {
-					hits = append(hits[:i], hits[i+1:]...)
-				}
+			if add {
+				hits = addHandler(hits, n.tag)
 			}
-		} else {
+			return true
+		})
+		if !p.pressed {
 			changed = true
 			p.handlers = hits
 		}
@@ -836,28 +812,34 @@ func (q *pointerQueue) deliverEnterLeaveEvents(cursor pointer.Cursor, p pointerI
 		if _, found := searchTag(hits, k); found {
 			continue
 		}
+		h, ok := handlers[k]
+		if !ok {
+			continue
+		}
 		changed = true
-		h := q.handlers[k]
 		e := e
 		e.Kind = pointer.Leave
 
-		if e.Kind&h.types != 0 {
-			e.Position = q.invTransform(h.area, e.Position)
+		if e.Kind&h.pointer.filter.kinds != 0 {
+			e.Position = q.invTransform(h.pointer.areaPlusOne-1, e.Position)
 			evts = append(evts, taggedEvent{tag: k, event: e})
 		}
 	}
 	// Deliver Enter events.
 	for _, k := range hits {
-		h := q.handlers[k]
 		if _, found := searchTag(p.entered, k); found {
 			continue
 		}
+		h, ok := handlers[k]
+		if !ok {
+			continue
+		}
 		changed = true
 		e := e
 		e.Kind = pointer.Enter
 
-		if e.Kind&h.types != 0 {
-			e.Position = q.invTransform(h.area, e.Position)
+		if e.Kind&h.pointer.filter.kinds != 0 {
+			e.Position = q.invTransform(h.pointer.areaPlusOne-1, e.Position)
 			evts = append(evts, taggedEvent{tag: k, event: e})
 		}
 	}
@@ -865,21 +847,21 @@ func (q *pointerQueue) deliverEnterLeaveEvents(cursor pointer.Cursor, p pointerI
 	return p, evts, cursor, changed
 }
 
-func (q *pointerQueue) deliverDragEvent(p pointerInfo, evts []taggedEvent) (pointerInfo, []taggedEvent) {
+func (q *pointerQueue) deliverDragEvent(handlers map[event.Tag]*handler, p pointerInfo, evts []taggedEvent) (pointerInfo, []taggedEvent) {
 	if p.dataSource != nil {
 		return p, evts
 	}
 	// Identify the data source.
 	for _, k := range p.entered {
-		src := q.handlers[k]
-		if len(src.sourceMimes) == 0 {
+		src := &handlers[k].pointer
+		if len(src.filter.sourceMimes) == 0 {
 			continue
 		}
 		// One data source handler per pointer.
 		p.dataSource = k
 		// Notify all potential targets.
-		for k, tgt := range q.handlers {
-			if _, ok := firstMimeMatch(src, tgt); ok {
+		for k, tgt := range handlers {
+			if _, ok := firstMimeMatch(src, &tgt.pointer); ok {
 				evts = append(evts, taggedEvent{tag: k, event: transfer.InitiateEvent{}})
 			}
 		}
@@ -888,30 +870,30 @@ func (q *pointerQueue) deliverDragEvent(p pointerInfo, evts []taggedEvent) (poin
 	return p, evts
 }
 
-func (q *pointerQueue) deliverDropEvent(p pointerInfo, evts []taggedEvent) (pointerInfo, []taggedEvent) {
+func (q *pointerQueue) deliverDropEvent(handlers map[event.Tag]*handler, p pointerInfo, evts []taggedEvent) (pointerInfo, []taggedEvent) {
 	if p.dataSource == nil {
 		return p, evts
 	}
 	// Request data from the source.
-	src := q.handlers[p.dataSource]
+	src := &handlers[p.dataSource].pointer
 	for _, k := range p.entered {
-		h := q.handlers[k]
-		if m, ok := firstMimeMatch(src, h); ok {
+		h := handlers[k]
+		if m, ok := firstMimeMatch(src, &h.pointer); ok {
 			p.dataTarget = k
 			evts = append(evts, taggedEvent{tag: p.dataSource, event: transfer.RequestEvent{Type: m}})
 			return p, evts
 		}
 	}
 	// No valid target found, abort.
-	return q.deliverTransferCancelEvent(p, evts)
+	return q.deliverTransferCancelEvent(handlers, p, evts)
 }
 
-func (q *pointerQueue) deliverTransferCancelEvent(p pointerInfo, evts []taggedEvent) (pointerInfo, []taggedEvent) {
+func (q *pointerQueue) deliverTransferCancelEvent(handlers map[event.Tag]*handler, p pointerInfo, evts []taggedEvent) (pointerInfo, []taggedEvent) {
 	evts = append(evts, taggedEvent{tag: p.dataSource, event: transfer.CancelEvent{}})
 	// Cancel all potential targets.
-	src := q.handlers[p.dataSource]
-	for k, h := range q.handlers {
-		if _, ok := firstMimeMatch(src, h); ok {
+	src := &handlers[p.dataSource].pointer
+	for k, h := range handlers {
+		if _, ok := firstMimeMatch(src, &h.pointer); ok {
 			evts = append(evts, taggedEvent{tag: k, event: transfer.CancelEvent{}})
 		}
 	}
@@ -953,8 +935,8 @@ func addHandler(tags []event.Tag, tag event.Tag) []event.Tag {
 
 // firstMimeMatch returns the first type match between src and tgt.
 func firstMimeMatch(src, tgt *pointerHandler) (first string, matched bool) {
-	for _, m1 := range tgt.targetMimes {
-		for _, m2 := range src.sourceMimes {
+	for _, m1 := range tgt.filter.targetMimes {
+		for _, m2 := range src.filter.sourceMimes {
 			if m1 == m2 {
 				return m1, true
 			}

io/input/router.go

@@ -27,6 +27,7 @@ import (
 type Router struct {
 	savedTrans []f32.Affine2D
 	transStack []f32.Affine2D
+	handlers   map[event.Tag]*handler
 	pointer    struct {
 		queue     pointerQueue
 		collector pointerCollector
@@ -101,6 +102,15 @@ const (
 // By convention, the zero value denotes the non-existent ID.
 type SemanticID uint
 
+// handler contains the per-handler state tracked by a [Router].
+type handler struct {
+	// active tracks whether the handler was active in the current
+	// frame. Router deletes state belonging to inactive handlers during Frame.
+	active  bool
+	pointer pointerHandler
+	key     keyHandler
+}
+
 // stateChange represents the new state and outgoing events
 // resulting from an incoming event.
 type stateChange struct {
@@ -153,25 +163,26 @@ func (s Source) Events(k event.Tag, filters ...event.Filter) []event.Event {
 
 func (q *Router) Events(k event.Tag, filters ...event.Filter) []event.Event {
 	var events []event.Event
+	h := q.stateFor(k)
 	// Record handler filters and add reset events.
 	for _, f := range filters {
 		switch f := f.(type) {
 		case key.Filter:
-			q.key.queue.filter(k, f)
+			h.key.Filter(f)
 		case key.FocusFilter:
-			q.key.queue.focusable(k)
-			if reset, ok := q.key.queue.ResetEvent(k); ok {
+			h.key.Focusable()
+			if reset, ok := h.key.ResetEvent(); ok {
 				events = append(events, reset)
 			}
 		case pointer.Filter:
-			q.pointer.queue.filterTag(k, f)
-			if reset, ok := q.pointer.queue.ResetEvent(k); ok {
+			h.pointer.Filter(k, f)
+			if reset, ok := h.pointer.ResetEvent(); ok {
 				events = append(events, reset)
 			}
 		case transfer.SourceFilter:
-			q.pointer.queue.sourceFilter(k, f)
+			h.pointer.SourceFilter(k, f)
 		case transfer.TargetFilter:
-			q.pointer.queue.targetFilter(k, f)
+			h.pointer.TargetFilter(k, f)
 		}
 	}
 	// Accumulate events from state changes until there are no more
@@ -225,15 +236,26 @@ func (q *Router) Frame(frame *op.Ops) {
 		state := q.changes[n-1].state
 		q.changes = append(q.changes[:0], stateChange{state: state})
 	}
+	for _, h := range q.handlers {
+		h.pointer.Reset()
+		h.key.Reset()
+	}
 	var ops *ops.Ops
 	if frame != nil {
 		ops = &frame.Internal
 	}
 	q.reader.Reset(ops)
 	q.collect()
+	for k, h := range q.handlers {
+		if !h.active {
+			delete(q.handlers, k)
+		} else {
+			h.active = false
+		}
+	}
 	q.executeCommands()
-	q.changePointerState(q.pointer.queue.Frame(q.lastState().pointerState))
-	kstate := q.key.queue.Frame(q.lastState().keyState)
+	q.changePointerState(q.pointer.queue.Frame(q.handlers, q.lastState().pointerState))
+	kstate := q.key.queue.Frame(q.handlers, q.lastState().keyState)
 	q.changeKeyState(kstate, nil)
 	// Collapse state and events.
 	q.collapseState(len(q.changes) - 1)
@@ -258,7 +280,7 @@ func (q *Router) processEvent(e event.Event) bool {
 	state := q.lastState()
 	switch e := e.(type) {
 	case pointer.Event:
-		return q.changePointerState(q.pointer.queue.Push(state.pointerState, e))
+		return q.changePointerState(q.pointer.queue.Push(q.handlers, state.pointerState, e))
 	case key.Event:
 		return q.addEvents(q.queueKeyEvent(state.keyState, e))
 	case key.SnippetEvent:
@@ -333,7 +355,7 @@ func (q *Router) executeCommands() {
 			kstate := q.key.queue.setSelection(state.keyState, req)
 			q.changeKeyState(kstate, nil)
 		case key.FocusCmd:
-			q.changeKeyState(q.key.queue.Focus(state.keyState, req.Tag))
+			q.changeKeyState(q.key.queue.Focus(q.handlers, state.keyState, req.Tag))
 		case key.SoftKeyboardCmd:
 			kstate := state.keyState.softKeyboard(req.Show)
 			q.changeKeyState(kstate, nil)
@@ -341,7 +363,7 @@ func (q *Router) executeCommands() {
 			kstate := q.key.queue.setSnippet(state.keyState, req)
 			q.changeKeyState(kstate, nil)
 		case transfer.OfferCmd:
-			q.changePointerState(q.pointer.queue.offerData(state.pointerState, req))
+			q.changePointerState(q.pointer.queue.offerData(q.handlers, state.pointerState, req))
 		case clipboard.WriteCmd:
 			q.cqueue.ProcessWriteClipboard(req)
 		case clipboard.ReadCmd:
@@ -404,10 +426,9 @@ func rangeNorm(r key.Range) key.Range {
 }
 
 func (q *Router) queueKeyEvent(state keyState, e key.Event) []taggedEvent {
-	kq := &q.key.queue
 	f := state.focus
 	var evts []taggedEvent
-	if f != nil && kq.Accepts(f, e) {
+	if f != nil && q.handlers[f].key.Accepts(e) {
 		evts = append(evts, taggedEvent{tag: f, event: e})
 		return evts
 	}
@@ -430,7 +451,7 @@ func (q *Router) queueKeyEvent(state keyState, e key.Event) []taggedEvent {
 		if n.tag == nil {
 			continue
 		}
-		if kq.Accepts(n.tag, e) {
+		if q.handlers[n.tag].key.Accepts(e) {
 			evts = append(evts, taggedEvent{tag: n.tag, event: e})
 			break
 		}
@@ -439,7 +460,7 @@ func (q *Router) queueKeyEvent(state keyState, e key.Event) []taggedEvent {
 }
 
 func (q *Router) MoveFocus(dir key.FocusDirection) bool {
-	ks, evts := q.key.queue.MoveFocus(q.lastState().keyState, dir)
+	ks, evts := q.key.queue.MoveFocus(q.handlers, q.lastState().keyState, dir)
 	return q.changeKeyState(ks, evts)
 }
 
@@ -451,8 +472,9 @@ func (q *Router) RevealFocus(viewport image.Rectangle) {
 	if focus == nil {
 		return
 	}
-	bounds := q.key.queue.BoundsFor(focus)
-	area := q.key.queue.AreaFor(focus)
+	kh := &q.handlers[focus].key
+	bounds := q.key.queue.BoundsFor(kh)
+	area := q.key.queue.AreaFor(kh)
 	viewport = q.pointer.queue.ClipFor(area, viewport)
 
 	topleft := bounds.Min.Sub(viewport.Min)
@@ -478,8 +500,9 @@ func (q *Router) ScrollFocus(dist image.Point) {
 	if focus == nil {
 		return
 	}
-	area := q.key.queue.AreaFor(focus)
-	q.addEvents(q.pointer.queue.Deliver(area, pointer.Event{
+	kh := &q.handlers[focus].key
+	area := q.key.queue.AreaFor(kh)
+	q.addEvents(q.pointer.queue.Deliver(q.handlers, area, pointer.Event{
 		Kind:   pointer.Scroll,
 		Source: pointer.Touch,
 		Scroll: f32internal.FPt(dist),
@@ -517,17 +540,18 @@ func (q *Router) ClickFocus() {
 	if focus == nil {
 		return
 	}
-	bounds := q.key.queue.BoundsFor(focus)
+	kh := &q.handlers[focus].key
+	bounds := q.key.queue.BoundsFor(kh)
 	center := bounds.Max.Add(bounds.Min).Div(2)
 	e := pointer.Event{
 		Position: f32.Pt(float32(center.X), float32(center.Y)),
 		Source:   pointer.Touch,
 	}
-	area := q.key.queue.AreaFor(focus)
+	area := q.key.queue.AreaFor(kh)
 	e.Kind = pointer.Press
-	q.addEvents(q.pointer.queue.Deliver(area, e))
+	q.addEvents(q.pointer.queue.Deliver(q.handlers, area, e))
 	e.Kind = pointer.Release
-	q.addEvents(q.pointer.queue.Deliver(area, e))
+	q.addEvents(q.pointer.queue.Deliver(q.handlers, area, e))
 }
 
 // TextInputState returns the input state from the most recent
@@ -540,7 +564,7 @@ func (q *Router) TextInputState() TextInputState {
 
 // TextInputHint returns the input mode from the most recent key.InputOp.
 func (q *Router) TextInputHint() (key.InputHint, bool) {
-	return q.key.queue.InputHint(q.state().keyState)
+	return q.key.queue.InputHint(q.handlers, q.state().keyState)
 }
 
 // WriteClipboard returns the most recent content to be copied
@@ -576,14 +600,27 @@ func (q *Router) AppendSemantics(nodes []SemanticNode) []SemanticNode {
 // EditorState returns the editor state for the focused handler, or the
 // zero value if there is none.
 func (q *Router) EditorState() EditorState {
-	return q.key.queue.editorState(q.state().keyState)
+	return q.key.queue.editorState(q.handlers, q.state().keyState)
+}
+
+func (q *Router) stateFor(tag event.Tag) *handler {
+	s, ok := q.handlers[tag]
+	if !ok {
+		s = new(handler)
+		if q.handlers == nil {
+			q.handlers = make(map[event.Tag]*handler)
+		}
+		q.handlers[tag] = s
+	}
+	s.active = true
+	return s
 }
 
 func (q *Router) collect() {
 	q.transStack = q.transStack[:0]
 	pc := &q.pointer.collector
 	pc.q = &q.pointer.queue
-	pc.reset()
+	pc.Reset()
 	kq := &q.key.queue
 	q.key.queue.Reset()
 	var t f32.Affine2D
@@ -628,10 +665,13 @@ func (q *Router) collect() {
 
 		case ops.TypeInput:
 			tag := encOp.Refs[0].(event.Tag)
-			pc.inputOp(tag)
+			s := q.stateFor(tag)
+			pc.inputOp(tag, &s.pointer)
 			a := pc.currentArea()
 			b := pc.currentAreaBounds()
-			kq.inputOp(tag, t, a, b)
+			if s.filter.focusable {
+				kq.inputOp(tag, &s.key, t, a, b)
+			}
 
 		// Pointer ops.
 		case ops.TypePass:
@@ -649,7 +689,8 @@ func (q *Router) collect() {
 				Tag:  encOp.Refs[0].(event.Tag),
 				Hint: key.InputHint(encOp.Data[1]),
 			}
-			kq.inputHint(op)
+			s := q.stateFor(op.Tag)
+			s.key.inputHint(op.Hint)
 
 		// Semantic ops.
 		case ops.TypeSemanticLabel: