io/pointer,io/router: [API] make pass-through a property of AreaOp

We're about to make operation scopes explicit, which would result in
both AreaOp and PassOp be scoped. However, PassOp seems to light to have
its separate stack, so this change instead makes pass-through a property
of an area. We're assuming that clients that want pass-through are also
aware of the affected hit area.

API change: replace PassOps with the AreaOp.PassThrough field.

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

internal/opconst/ops.go

@@ -19,7 +19,6 @@ const (
 	TypeLinearGradient
 	TypeArea
 	TypePointerInput
-	TypePass
 	TypeClipboardRead
 	TypeClipboardWrite
 	TypeKeyInput
@@ -45,9 +44,8 @@ const (
 	TypePaintLen           = 1
 	TypeColorLen           = 1 + 4
 	TypeLinearGradientLen  = 1 + 8*2 + 4*2
-	TypeAreaLen            = 1 + 1 + 4*4
+	TypeAreaLen            = 1 + 1 + 1 + 4*4
 	TypePointerInputLen    = 1 + 1 + 1 + 2*4 + 2*4
-	TypePassLen            = 1 + 1
 	TypeClipboardReadLen   = 1
 	TypeClipboardWriteLen  = 1
 	TypeKeyInputLen        = 1 + 1
@@ -90,7 +88,6 @@ func (t OpType) Size() int {
 		TypeLinearGradientLen,
 		TypeAreaLen,
 		TypePointerInputLen,
-		TypePassLen,
 		TypeClipboardReadLen,
 		TypeClipboardWriteLen,
 		TypeKeyInputLen,
@@ -142,8 +139,6 @@ func (t OpType) String() string {
 		return "Area"
 	case TypePointerInput:
 		return "PointerInput"
-	case TypePass:
-		return "Pass"
 	case TypeClipboardRead:
 		return "ClipboardRead"
 	case TypeClipboardWrite:

io/pointer/doc.go

@@ -65,14 +65,17 @@ When determining which handlers match an Event, only handlers whose
 areas contain the event position are considered. The matching
 proceeds as follows.
 
-First, the foremost matching handler is included. If the handler
+First, the foremost area that contains the event is found. If no such area
-has pass-through enabled, this step is repeated.
+exists, matching stops.
 
-Then, all matching handlers from the current node and all parent
+Then, every handler attached to the area or an area in the area stack is
-nodes are included.
+matched with the event.
+
+Third, If the area or any area in the area stack has pass-through enabled,
+the matching repeats with the next foremost area.
 
 In the example above, all events will go to h2 only even though both
-handlers have the same area (the entire screen).
+handlers have the same area (the implicit area that fills the window).
 
 Pass-through
 

io/pointer/pointer.go

@@ -46,6 +46,10 @@ type Event struct {
 // hit area and the area. The area is transformed before applying
 // it.
 type AreaOp struct {
+	// PassThrough areas and their children don't block events to siblings
+	// them.
+	PassThrough bool
+
 	kind areaKind
 	rect image.Rectangle
 }
@@ -72,11 +76,6 @@ type InputOp struct {
 	ScrollBounds image.Rectangle
 }
 
-// PassOp sets the pass-through mode.
-type PassOp struct {
-	Pass bool
-}
-
 type ID uint16
 
 // Type of an Event.
@@ -190,11 +189,14 @@ func (op AreaOp) Add(o *op.Ops) {
 	data := o.Write(opconst.TypeAreaLen)
 	data[0] = byte(opconst.TypeArea)
 	data[1] = byte(op.kind)
+	if op.PassThrough {
+		data[2] = 1
+	}
 	bo := binary.LittleEndian
-	bo.PutUint32(data[2:], uint32(op.rect.Min.X))
+	bo.PutUint32(data[3:], uint32(op.rect.Min.X))
-	bo.PutUint32(data[6:], uint32(op.rect.Min.Y))
+	bo.PutUint32(data[7:], uint32(op.rect.Min.Y))
-	bo.PutUint32(data[10:], uint32(op.rect.Max.X))
+	bo.PutUint32(data[11:], uint32(op.rect.Max.X))
-	bo.PutUint32(data[14:], uint32(op.rect.Max.Y))
+	bo.PutUint32(data[15:], uint32(op.rect.Max.Y))
 }
 
 func (op CursorNameOp) Add(o *op.Ops) {
@@ -223,14 +225,6 @@ func (op InputOp) Add(o *op.Ops) {
 	bo.PutUint32(data[15:], uint32(op.ScrollBounds.Max.Y))
 }
 
-func (op PassOp) Add(o *op.Ops) {
-	data := o.Write(opconst.TypePassLen)
-	data[0] = byte(opconst.TypePass)
-	if op.Pass {
-		data[1] = 1
-	}
-}
-
 func (t Type) String() string {
 	switch t {
 	case Press:

io/router/pointer.go

@@ -31,8 +31,6 @@ type pointerQueue struct {
 type hitNode struct {
 	next int
 	area int
-	// Pass tracks the most recent PassOp mode.
-	pass bool
 
 	// For handler nodes.
 	tag event.Tag
@@ -65,6 +63,7 @@ type pointerHandler struct {
 }
 
 type areaOp struct {
+	pass bool
 	kind areaKind
 	rect f32.Rectangle
 }
@@ -73,6 +72,7 @@ type areaNode struct {
 	trans f32.Affine2D
 	next  int
 	area  areaOp
+	pass  bool
 }
 
 type areaKind uint8
@@ -81,7 +81,6 @@ type areaKind uint8
 type collectState struct {
 	t    f32.Affine2D
 	node int
-	pass bool
 }
 
 const (
@@ -115,20 +114,18 @@ func (q *pointerQueue) collectHandlers(r *ops.Reader, events *handlerEvents) {
 			if mask&^opconst.TransformState != 0 {
 				state = s
 			}
-		case opconst.TypePass:
-			state.pass = encOp.Data[1] != 0
 		case opconst.TypeArea:
 			var op areaOp
 			op.Decode(encOp.Data)
 			area := -1
-			if n := state.node; n != -1 {
+			if i := state.node; i != -1 {
-				area = q.hitTree[n].area
+				n := q.hitTree[i]
+				area = n.area
 			}
-			q.areas = append(q.areas, areaNode{trans: state.t, next: area, area: op})
+			q.areas = append(q.areas, areaNode{trans: state.t, next: area, area: op, pass: op.pass})
 			q.hitTree = append(q.hitTree, hitNode{
 				next: state.node,
 				area: len(q.areas) - 1,
-				pass: state.pass,
 			})
 			state.node = len(q.hitTree) - 1
 		case opconst.TypeTransform:
@@ -141,13 +138,13 @@ func (q *pointerQueue) collectHandlers(r *ops.Reader, events *handlerEvents) {
 				Types: pointer.Type(encOp.Data[2]),
 			}
 			area := -1
-			if n := state.node; n != -1 {
+			if i := state.node; i != -1 {
-				area = q.hitTree[n].area
+				n := q.hitTree[i]
+				area = n.area
 			}
 			q.hitTree = append(q.hitTree, hitNode{
 				next: state.node,
 				area: area,
-				pass: state.pass,
 				tag:  op.Tag,
 			})
 			state.node = len(q.hitTree) - 1
@@ -189,11 +186,12 @@ func (q *pointerQueue) opHit(handlers *[]event.Tag, pos f32.Point) {
 	idx := len(q.hitTree) - 1
 	for idx >= 0 {
 		n := &q.hitTree[idx]
-		if !q.hit(n.area, pos) {
+		hit, areaPass := q.hit(n.area, pos)
+		if !hit {
 			idx--
 			continue
 		}
-		pass = pass && n.pass
+		pass = pass && areaPass
 		if pass {
 			idx--
 		} else {
@@ -214,16 +212,18 @@ func (q *pointerQueue) invTransform(areaIdx int, p f32.Point) f32.Point {
 	return q.areas[areaIdx].trans.Invert().Transform(p)
 }
 
-func (q *pointerQueue) hit(areaIdx int, p f32.Point) bool {
+func (q *pointerQueue) hit(areaIdx int, p f32.Point) (bool, bool) {
+	pass := false
 	for areaIdx != -1 {
 		a := &q.areas[areaIdx]
 		p := a.trans.Invert().Transform(p)
 		if !a.area.Hit(p) {
-			return false
+			return false, false
 		}
 		areaIdx = a.next
+		pass = pass || a.pass
 	}
-	return true
+	return true, pass
 }
 
 func (q *pointerQueue) reset() {
@@ -466,17 +466,18 @@ func (op *areaOp) Decode(d []byte) {
 	}
 	rect := f32.Rectangle{
 		Min: f32.Point{
-			X: opDecodeFloat32(d[2:]),
+			X: opDecodeFloat32(d[3:]),
-			Y: opDecodeFloat32(d[6:]),
+			Y: opDecodeFloat32(d[7:]),
 		},
 		Max: f32.Point{
-			X: opDecodeFloat32(d[10:]),
+			X: opDecodeFloat32(d[11:]),
-			Y: opDecodeFloat32(d[14:]),
+			Y: opDecodeFloat32(d[15:]),
 		},
 	}
 	*op = areaOp{
 		kind: areaKind(d[1]),
 		rect: rect,
+		pass: d[2] != 0,
 	}
 }
 

widget/example_test.go

@@ -28,11 +28,12 @@ func ExampleClickable_passthrough() {
 
 	// widget lays out two buttons on top of each other.
 	widget := func() {
-		// button2 completely covers button1, but PassOp allows pointer
-		// events to pass through to button1.
 		button1.Layout(gtx)
-		// PassOp is applied to the area defined by button1.
+		area := pointer.Rect(image.Rectangle{Max: gtx.Constraints.Max})
-		pointer.PassOp{Pass: true}.Add(gtx.Ops)
+		// button2 completely covers button1, but pass-through allows pointer
+		// events to pass through to button1.
+		area.PassThrough = true
+		area.Add(gtx.Ops)
 		button2.Layout(gtx)
 	}
 

widget/material/list.go

@@ -162,7 +162,7 @@ func (s ScrollbarStyle) layout(gtx layout.Context, axis layout.Axis, viewportSta
 			// Stack a normal clickable area on top of the draggable area
 			// to capture non-dragging clicks.
 			saved := op.Save(gtx.Ops)
-			pointer.PassOp{Pass: true}.Add(gtx.Ops)
+			pointerArea.PassThrough = true
 			pointerArea.Add(gtx.Ops)
 			s.Scrollbar.AddTrack(gtx.Ops)
 			saved.Load()
@@ -208,8 +208,9 @@ func (s ScrollbarStyle) layout(gtx layout.Context, axis layout.Axis, viewportSta
 				}.Op(gtx.Ops))
 
 				// Add the indicator pointer hit area.
-				pointer.PassOp{Pass: true}.Add(gtx.Ops)
+				area := pointer.Rect(image.Rectangle{Max: indicatorDims})
-				pointer.Rect(image.Rectangle{Max: indicatorDims}).Add(gtx.Ops)
+				area.PassThrough = true
+				area.Add(gtx.Ops)
 				s.Scrollbar.AddIndicator(gtx.Ops)
 
 				return layout.Dimensions{Size: axis.Convert(gtx.Constraints.Min)}