ui: add package input for merged input

To avoid passing a queue type for each kind of input (pointer, key),
introduce package input for mapping a handler key to all input events.

Future input sources can be added without changes to programs, and
as an added bonus, event ordering is preserved across input sources.

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

ui/input/queue.go

@@ -0,0 +1,53 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+package input
+
+import (
+	"gioui.org/ui"
+	"gioui.org/ui/key"
+	"gioui.org/ui/pointer"
+)
+
+// Queue is an Events implementation that merges events from
+// all available input sources.
+type Queue struct {
+	pqueue pointerQueue
+	kqueue keyQueue
+
+	handlers handlerEvents
+}
+
+type handlerEvents map[Key][]Event
+
+func (q *Queue) For(k Key) []Event {
+	return q.handlers[k]
+}
+
+func (q *Queue) Frame(ops *ui.Ops) {
+	q.init()
+	for k := range q.handlers {
+		delete(q.handlers, k)
+	}
+	q.pqueue.Frame(ops, q.handlers)
+	q.kqueue.Frame(ops, q.handlers)
+}
+
+func (q *Queue) Add(e Event) {
+	q.init()
+	switch e := e.(type) {
+	case pointer.Event:
+		q.pqueue.Push(e, q.handlers)
+	case key.Edit, key.Chord, key.Focus:
+		q.kqueue.Push(e, q.handlers)
+	}
+}
+
+func (q *Queue) InputState() key.TextInputState {
+	return q.kqueue.InputState()
+}
+
+func (q *Queue) init() {
+	if q.handlers == nil {
+		q.handlers = make(handlerEvents)
+	}
+}