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>

io/input/router.go

@@ -119,16 +119,27 @@ func (s Source) Enabled() bool {
 	return s.r != nil
 }
 
-// Events returns the available events for the handler tag.
-func (s Source) Events(k event.Tag) []event.Event {
+// Events returns the events for the handler tag that matches one
+// or more of filters.
+func (s Source) Events(k event.Tag, filters ...event.Filter) []event.Event {
 	if !s.Enabled() {
 		return nil
 	}
-	return s.r.Events(k)
+	return s.r.Events(k, filters...)
 }
 
-func (q *Router) Events(k event.Tag) []event.Event {
-	events := q.handlers.Events(k)
+func (q *Router) Events(k event.Tag, filters ...event.Filter) []event.Event {
+	for _, f := range filters {
+		switch f := f.(type) {
+		case pointer.Filter:
+			q.pointer.queue.filterTag(k, f, &q.handlers)
+		case transfer.SourceFilter:
+			q.pointer.queue.sourceFilter(k, f, &q.handlers)
+		case transfer.TargetFilter:
+			q.pointer.queue.targetFilter(k, f, &q.handlers)
+		}
+	}
+	events := q.handlers.Events(k, filters...)
 	return events
 }
 
@@ -424,7 +435,6 @@ func (q *Router) collect() {
 	kq := &q.key.queue
 	q.key.queue.Reset()
 	var t f32.Affine2D
-	bo := binary.LittleEndian
 	for encOp, ok := q.reader.Decode(); ok; encOp, ok = q.reader.Decode() {
 		switch ops.OpType(encOp.Data[0]) {
 		case ops.TypeInvalidate:
@@ -464,42 +474,18 @@ func (q *Router) collect() {
 			q.transStack = q.transStack[:n-1]
 			pc.setTrans(t)
 
+		case ops.TypeInput:
+			tag := encOp.Refs[0].(event.Tag)
+			pc.inputOp(tag, &q.handlers)
+
 		// Pointer ops.
 		case ops.TypePass:
 			pc.pass()
 		case ops.TypePopPass:
 			pc.popPass()
-		case ops.TypePointerInput:
-			op := pointer.InputOp{
-				Tag:   encOp.Refs[0].(event.Tag),
-				Kinds: pointer.Kind(bo.Uint16(encOp.Data[1:])),
-				ScrollBounds: image.Rectangle{
-					Min: image.Point{
-						X: int(int32(bo.Uint32(encOp.Data[3:]))),
-						Y: int(int32(bo.Uint32(encOp.Data[7:]))),
-					},
-					Max: image.Point{
-						X: int(int32(bo.Uint32(encOp.Data[11:]))),
-						Y: int(int32(bo.Uint32(encOp.Data[15:]))),
-					},
-				},
-			}
-			pc.inputOp(op, &q.handlers)
 		case ops.TypeCursor:
 			name := pointer.Cursor(encOp.Data[1])
 			pc.cursor(name)
-		case ops.TypeSource:
-			op := transfer.SourceOp{
-				Tag:  encOp.Refs[0].(event.Tag),
-				Type: encOp.Refs[1].(string),
-			}
-			pc.sourceOp(op, &q.handlers)
-		case ops.TypeTarget:
-			op := transfer.TargetOp{
-				Tag:  encOp.Refs[0].(event.Tag),
-				Type: encOp.Refs[1].(string),
-			}
-			pc.targetOp(op, &q.handlers)
 		case ops.TypeActionInput:
 			act := system.Action(encOp.Data[1])
 			pc.actionInputOp(act)
@@ -570,12 +556,55 @@ func (h *handlerEvents) HadEvents() bool {
 	return u
 }
 
-func (h *handlerEvents) Events(k event.Tag) []event.Event {
+func (h *handlerEvents) Events(k event.Tag, filters ...event.Filter) []event.Event {
+	var filtered []event.Event
 	if events, ok := h.handlers[k]; ok {
-		h.handlers[k] = h.handlers[k][:0]
-		return events
+		i := 0
+		for i < len(events) {
+			e := events[i]
+			if filtersMatches(filters, e) {
+				filtered = append(filtered, e)
+				events = append(events[:i], events[i+1:]...)
+			} else {
+				i++
+			}
+		}
+		h.handlers[k] = events
 	}
-	return nil
+	return filtered
+}
+
+func filtersMatches(filters []event.Filter, e event.Event) bool {
+	switch e := e.(type) {
+	case pointer.Event:
+		for _, f := range filters {
+			if f, ok := f.(pointer.Filter); ok && f.Kinds&e.Kind == e.Kind {
+				return true
+			}
+		}
+	case transfer.CancelEvent, transfer.InitiateEvent:
+		for _, f := range filters {
+			switch f.(type) {
+			case transfer.SourceFilter, transfer.TargetFilter:
+				return true
+			}
+		}
+	case transfer.RequestEvent:
+		for _, f := range filters {
+			if f, ok := f.(transfer.SourceFilter); ok && f.Type == e.Type {
+				return true
+			}
+		}
+	case transfer.DataEvent:
+		for _, f := range filters {
+			if f, ok := f.(transfer.TargetFilter); ok && f.Type == e.Type {
+				return true
+			}
+		}
+	default:
+		return true
+	}
+	return false
 }
 
 func (h *handlerEvents) Clear() {