io/input,io/key: [API] introduce Command, replace FocusOp with FocusCmd

Modeling focus change as an operation is awkward, because focus changes
logically happen during event processing, not layout. In particular, you
want to apply focus changes even if a widget is subsequently never laid
out.

Now that input.Source is concrete, it's much more straightforward to
offer focus changes as a command which can be queued through the
Source. A future change may similarly offer a command for directional
focus changes.

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

io/input/router.go

@@ -33,8 +33,7 @@ type Router struct {
 		collector pointerCollector
 	}
 	key struct {
-		queue     keyQueue
-		collector keyCollector
+		queue keyQueue
 	}
 	cqueue clipboardQueue
 
@@ -45,6 +44,9 @@ type Router struct {
 	// InvalidateOp summary.
 	wakeup     bool
 	wakeupTime time.Time
+
+	// Changes queued for next call to Frame.
+	commands []Command
 }
 
 // Source implements the interface between a Router and user interface widgets.
@@ -53,6 +55,12 @@ type Source struct {
 	r *Router
 }
 
+// Command represents a request such as moving the focus, or initiating a clipboard read.
+// Commands are queued by calling [Source.Queue].
+type Command interface {
+	ImplementsCommand()
+}
+
 // SemanticNode represents a node in the tree describing the components
 // contained in a frame.
 type SemanticNode struct {
@@ -98,6 +106,15 @@ func (q *Router) Source() Source {
 	return Source{r: q}
 }
 
+// Queue a command to be executed after the current frame
+// has completed.
+func (s Source) Queue(c Command) {
+	if !s.Enabled() {
+		return
+	}
+	s.r.queue(c)
+}
+
 // Enabled reports whether the source is enabled. Only enabled
 // Sources deliver events and respond to commands.
 func (s Source) Enabled() bool {
@@ -129,9 +146,10 @@ func (q *Router) Frame(frame *op.Ops) {
 	}
 	q.reader.Reset(ops)
 	q.collect()
-
+	q.executeCommands()
 	q.pointer.queue.Frame(&q.handlers)
-	q.key.queue.Frame(&q.handlers, q.key.collector)
+	q.key.queue.Frame(&q.handlers)
+
 	if q.handlers.HadEvents() {
 		q.wakeup = true
 		q.wakeupTime = time.Time{}
@@ -189,6 +207,20 @@ func (q *Router) Queue(events ...event.Event) bool {
 	return q.handlers.HadEvents()
 }
 
+func (q *Router) queue(f Command) {
+	q.commands = append(q.commands, f)
+}
+
+func (q *Router) executeCommands() {
+	for _, req := range q.commands {
+		switch req := req.(type) {
+		case key.FocusCmd:
+			q.key.queue.Focus(req.Tag, &q.handlers)
+		}
+	}
+	q.commands = nil
+}
+
 func rangeOverlaps(r1, r2 key.Range) bool {
 	r1 = rangeNorm(r1)
 	r2 = rangeNorm(r2)
@@ -377,8 +409,7 @@ func (q *Router) collect() {
 	pc := &q.pointer.collector
 	pc.q = &q.pointer.queue
 	pc.reset()
-	kc := &q.key.collector
-	*kc = keyCollector{q: &q.key.queue}
+	kq := &q.key.queue
 	q.key.queue.Reset()
 	var t f32.Affine2D
 	bo := binary.LittleEndian
@@ -473,18 +504,11 @@ func (q *Router) collect() {
 			act := system.Action(encOp.Data[1])
 			pc.actionInputOp(act)
 
-		// Key ops.
-		case ops.TypeKeyFocus:
-			tag, _ := encOp.Refs[0].(event.Tag)
-			op := key.FocusOp{
-				Tag: tag,
-			}
-			kc.focusOp(op.Tag)
 		case ops.TypeKeySoftKeyboard:
 			op := key.SoftKeyboardOp{
 				Show: encOp.Data[1] != 0,
 			}
-			kc.softKeyboard(op.Show)
+			kq.softKeyboard(op.Show)
 		case ops.TypeKeyInput:
 			filter := key.Set(*encOp.Refs[1].(*string))
 			op := key.InputOp{
@@ -495,7 +519,7 @@ func (q *Router) collect() {
 			a := pc.currentArea()
 			b := pc.currentAreaBounds()
 			pc.keyInputOp(op)
-			kc.inputOp(op, a, b)
+			kq.inputOp(op, a, b)
 		case ops.TypeSnippet:
 			op := key.SnippetOp{
 				Tag: encOp.Refs[0].(event.Tag),
@@ -507,7 +531,7 @@ func (q *Router) collect() {
 					Text: *(encOp.Refs[1].(*string)),
 				},
 			}
-			kc.snippetOp(op)
+			kq.snippetOp(op)
 		case ops.TypeSelection:
 			op := key.SelectionOp{
 				Tag: encOp.Refs[0].(event.Tag),
@@ -524,7 +548,7 @@ func (q *Router) collect() {
 					Descent: math.Float32frombits(bo.Uint32(encOp.Data[21:])),
 				},
 			}
-			kc.selectionOp(t, op)
+			kq.selectionOp(t, op)
 
 		// Semantic ops.
 		case ops.TypeSemanticLabel: