io: [API] introduce event filters; convert pointer input to use them

Instead of having to supply the predicates for event filtering at the
time of layout, the new Filter type allows widgets to filter at the time
of calling Source.Events. There is then only the need for a single input
op type, in package event.

Filters most importantly allow the use of one tag for several event types,
and we can define that a widget w has &w as its primary tag, by convention.
This allows the replacement of per-widget Focus methods with direct uses
of FocusCmd{&w}, and the later addition of Source.Focused(&w) queries.

Note that the TestCursor test needed restructuring to avoid its use of
InputOps.

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

gesture/gesture.go

@@ -17,6 +17,7 @@ import (
 
 	"gioui.org/f32"
 	"gioui.org/internal/fling"
+	"gioui.org/io/event"
 	"gioui.org/io/input"
 	"gioui.org/io/key"
 	"gioui.org/io/pointer"
@@ -37,15 +38,12 @@ type Hover struct {
 
 // Add the gesture to detect hovering over the current pointer area.
 func (h *Hover) Add(ops *op.Ops) {
-	pointer.InputOp{
-		Tag:   h,
-		Kinds: pointer.Enter | pointer.Leave,
-	}.Add(ops)
+	event.InputOp(ops, h)
 }
 
 // Update state and report whether a pointer is inside the area.
 func (h *Hover) Update(q input.Source) bool {
-	for _, ev := range q.Events(h) {
+	for _, ev := range q.Events(h, pointer.Filter{Kinds: pointer.Enter | pointer.Leave}) {
 		e, ok := ev.(pointer.Event)
 		if !ok {
 			continue
@@ -114,7 +112,6 @@ type Drag struct {
 // movements as well as drag and fling touch gestures.
 type Scroll struct {
 	dragging  bool
-	axis      Axis
 	estimator fling.Extrapolation
 	flinger   fling.Animation
 	pid       pointer.ID
@@ -159,10 +156,7 @@ const touchSlop = unit.Dp(3)
 
 // Add the handler to the operation list to receive click events.
 func (c *Click) Add(ops *op.Ops) {
-	pointer.InputOp{
-		Tag:   c,
-		Kinds: pointer.Press | pointer.Release | pointer.Enter | pointer.Leave,
-	}.Add(ops)
+	event.InputOp(ops, c)
 }
 
 // Hovered returns whether a pointer is inside the area.
@@ -178,7 +172,7 @@ func (c *Click) Pressed() bool {
 // Update state and return the click events.
 func (c *Click) Update(q input.Source) []ClickEvent {
 	var events []ClickEvent
-	for _, evt := range q.Events(c) {
+	for _, evt := range q.Events(c, pointer.Filter{Kinds: pointer.Press | pointer.Release | pointer.Enter | pointer.Leave}) {
 		e, ok := evt.(pointer.Event)
 		if !ok {
 			continue
@@ -248,13 +242,8 @@ func (ClickEvent) ImplementsEvent() {}
 // Add the handler to the operation list to receive scroll events.
 // The bounds variable refers to the scrolling boundaries
 // as defined in io/pointer.InputOp.
-func (s *Scroll) Add(ops *op.Ops, bounds image.Rectangle) {
-	oph := pointer.InputOp{
-		Tag:          s,
-		Kinds:        pointer.Press | pointer.Drag | pointer.Release | pointer.Scroll,
-		ScrollBounds: bounds,
-	}
-	oph.Add(ops)
+func (s *Scroll) Add(ops *op.Ops) {
+	event.InputOp(ops, s)
 	if s.flinger.Active() {
 		op.InvalidateOp{}.Add(ops)
 	}
@@ -266,13 +255,13 @@ func (s *Scroll) Stop() {
 }
 
 // Update state and report the scroll distance along axis.
-func (s *Scroll) Update(cfg unit.Metric, q input.Source, t time.Time, axis Axis) int {
-	if s.axis != axis {
-		s.axis = axis
-		return 0
-	}
+func (s *Scroll) Update(cfg unit.Metric, q input.Source, t time.Time, axis Axis, bounds image.Rectangle) int {
 	total := 0
-	for _, evt := range q.Events(s) {
+	f := pointer.Filter{
+		Kinds:        pointer.Press | pointer.Drag | pointer.Release | pointer.Scroll,
+		ScrollBounds: bounds,
+	}
+	for _, evt := range q.Events(s, f) {
 		e, ok := evt.(pointer.Event)
 		if !ok {
 			continue
@@ -289,7 +278,7 @@ func (s *Scroll) Update(cfg unit.Metric, q input.Source, t time.Time, axis Axis)
 			}
 			s.Stop()
 			s.estimator = fling.Extrapolation{}
-			v := s.val(e.Position)
+			v := s.val(axis, e.Position)
 			s.last = int(math.Round(float64(v)))
 			s.estimator.Sample(e.Time, v)
 			s.dragging = true
@@ -306,7 +295,7 @@ func (s *Scroll) Update(cfg unit.Metric, q input.Source, t time.Time, axis Axis)
 		case pointer.Cancel:
 			s.dragging = false
 		case pointer.Scroll:
-			switch s.axis {
+			switch axis {
 			case Horizontal:
 				s.scroll += e.Scroll.X
 			case Vertical:
@@ -319,7 +308,7 @@ func (s *Scroll) Update(cfg unit.Metric, q input.Source, t time.Time, axis Axis)
 			if !s.dragging || s.pid != e.PointerID {
 				continue
 			}
-			val := s.val(e.Position)
+			val := s.val(axis, e.Position)
 			s.estimator.Sample(e.Time, val)
 			v := int(math.Round(float64(val)))
 			dist := s.last - v
@@ -338,8 +327,8 @@ func (s *Scroll) Update(cfg unit.Metric, q input.Source, t time.Time, axis Axis)
 	return total
 }
 
-func (s *Scroll) val(p f32.Point) float32 {
-	if s.axis == Horizontal {
+func (s *Scroll) val(axis Axis, p f32.Point) float32 {
+	if axis == Horizontal {
 		return p.X
 	} else {
 		return p.Y
@@ -360,16 +349,13 @@ func (s *Scroll) State() ScrollState {
 
 // Add the handler to the operation list to receive drag events.
 func (d *Drag) Add(ops *op.Ops) {
-	pointer.InputOp{
-		Tag:   d,
-		Kinds: pointer.Press | pointer.Drag | pointer.Release,
-	}.Add(ops)
+	event.InputOp(ops, d)
 }
 
 // Update state and return the drag events.
 func (d *Drag) Update(cfg unit.Metric, q input.Source, axis Axis) []pointer.Event {
 	var events []pointer.Event
-	for _, e := range q.Events(d) {
+	for _, e := range q.Events(d, pointer.Filter{Kinds: pointer.Press | pointer.Drag | pointer.Release}) {
 		e, ok := e.(pointer.Event)
 		if !ok {
 			continue

gesture/gesture_test.go

@@ -23,6 +23,7 @@ func TestHover(t *testing.T) {
 	h.Add(ops)
 	stack.Pop()
 	r := new(input.Router)
+	h.Update(r.Source())
 	r.Frame(ops)
 
 	r.Queue(
@@ -72,6 +73,7 @@ func TestMouseClicks(t *testing.T) {
 			click.Add(&ops)
 
 			var r input.Router
+			click.Update(r.Source())
 			r.Frame(&ops)
 			r.Queue(tc.events...)