io/clipboard,app: add WriteOp, ReadOp

Previously, the only way to manipulate the clipboard (read or write) is
using the `app.Window`.

The new `clipboard.ReadOp` and `clipboard.WriteOp`makes possible to
read/write from the widget.

Signed-off-by: Inkeliz <inkeliz@inkeliz.com>

io/router/router.go

@@ -16,6 +16,7 @@ import (
 
 	"gioui.org/internal/opconst"
 	"gioui.org/internal/ops"
+	"gioui.org/io/clipboard"
 	"gioui.org/io/event"
 	"gioui.org/io/key"
 	"gioui.org/io/pointer"
@@ -28,6 +29,7 @@ import (
 type Router struct {
 	pqueue pointerQueue
 	kqueue keyQueue
+	cqueue clipboardQueue
 
 	handlers handlerEvents
 
@@ -88,6 +90,8 @@ func (q *Router) Add(events ...event.Event) bool {
 			q.pqueue.Push(e, &q.handlers)
 		case key.EditEvent, key.Event, key.FocusEvent:
 			q.kqueue.Push(e, &q.handlers)
+		case clipboard.Event:
+			q.cqueue.Push(e, &q.handlers)
 		}
 	}
 	return q.handlers.HadEvents()
@@ -99,6 +103,18 @@ func (q *Router) TextInputState() TextInputState {
 	return q.kqueue.InputState()
 }
 
+// WriteClipboard returns the most recent text to be copied
+// to the clipboard, if any.
+func (q *Router) WriteClipboard() (string, bool) {
+	return q.cqueue.WriteClipboard()
+}
+
+// ReadClipboard reports if any new handler is waiting
+// to read the clipboard.
+func (q *Router) ReadClipboard() bool {
+	return q.cqueue.ReadClipboard()
+}
+
 func (q *Router) collect() {
 	for encOp, ok := q.reader.Decode(); ok; encOp, ok = q.reader.Decode() {
 		switch opconst.OpType(encOp.Data[0]) {
@@ -115,6 +131,10 @@ func (q *Router) collect() {
 			}
 			q.profiling = true
 			q.profHandlers[op.Tag] = struct{}{}
+		case opconst.TypeClipboardRead:
+			q.cqueue.ProcessReadClipboard(encOp.Data, encOp.Refs)
+		case opconst.TypeClipboardWrite:
+			q.cqueue.ProcessWriteClipboard(encOp.Data, encOp.Refs)
 		}
 	}
 }