app,io/system: extract system events to separate package

Package app is the only package that depends on native libraries and
Cgo. Minimize its API, thereby minimizing Gio clients' dependency on
it. In the future, a headless, testing or remote "Window" should be
very easy to replace app.Window.

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

app/window.go

@@ -12,6 +12,7 @@ import (
 	"gioui.org/app/internal/input"
 	"gioui.org/io/event"
 	"gioui.org/io/profile"
+	"gioui.org/io/system"
 	"gioui.org/op"
 	"gioui.org/unit"
 )
@@ -24,6 +25,12 @@ type windowOptions struct {
 	Title         string
 }
 
+type frameEvent struct {
+	system.FrameEvent
+
+	sync bool
+}
+
 // Window represents an operating system window.
 type Window struct {
 	driver    *window
@@ -37,7 +44,7 @@ type Window struct {
 	invalidates chan struct{}
 	frames      chan *op.Ops
 
-	stage        Stage
+	stage        system.Stage
 	animating    bool
 	hasNextFrame bool
 	nextFrame    time.Time
@@ -170,7 +177,7 @@ func (w *Window) updateAnimation() {
 		w.delayedDraw.Stop()
 		w.delayedDraw = nil
 	}
-	if w.stage >= StageRunning && w.hasNextFrame {
+	if w.stage >= system.StageRunning && w.hasNextFrame {
 		if dt := time.Until(w.nextFrame); dt <= 0 {
 			animate = true
 		} else {
@@ -210,10 +217,10 @@ func (w *Window) waitAck() {
 func (w *Window) destroy(err error) {
 	// Ack the current event.
 	w.ack <- struct{}{}
-	w.out <- DestroyEvent{err}
+	w.out <- system.DestroyEvent{Err: err}
 	for e := range w.in {
 		w.ack <- struct{}{}
-		if _, ok := e.(DestroyEvent); ok {
+		if _, ok := e.(system.DestroyEvent); ok {
 			return
 		}
 	}
@@ -223,7 +230,7 @@ func (w *Window) run(opts *windowOptions) {
 	defer close(w.in)
 	defer close(w.out)
 	if err := createWindow(w, opts); err != nil {
-		w.out <- DestroyEvent{err}
+		w.out <- system.DestroyEvent{Err: err}
 		return
 	}
 	for {
@@ -240,9 +247,9 @@ func (w *Window) run(opts *windowOptions) {
 			w.updateAnimation()
 		case e := <-w.in:
 			switch e2 := e.(type) {
-			case StageEvent:
+			case system.StageEvent:
 				if w.gpu != nil {
-					if e2.Stage < StageRunning {
+					if e2.Stage < system.StageRunning {
 						w.gpu.Release()
 						w.gpu = nil
 					} else {
@@ -253,18 +260,18 @@ func (w *Window) run(opts *windowOptions) {
 				w.updateAnimation()
 				w.out <- e
 				w.waitAck()
-			case FrameEvent:
+			case frameEvent:
 				if e2.Size == (image.Point{}) {
 					panic(errors.New("internal error: zero-sized Draw"))
 				}
-				if w.stage < StageRunning {
+				if w.stage < system.StageRunning {
 					// No drawing if not visible.
 					break
 				}
 				w.drawStart = time.Now()
 				w.hasNextFrame = false
 				e2.Frame = w.update
-				w.out <- e2
+				w.out <- e2.FrameEvent
 				var frame *op.Ops
 				// Wait for either a frame or the ack event,
 				// which meant that the client didn't draw.
@@ -303,12 +310,12 @@ func (w *Window) run(opts *windowOptions) {
 						return
 					}
 				}
-			case *CommandEvent:
+			case *system.CommandEvent:
 				w.out <- e
 				w.waitAck()
 			case driverEvent:
 				w.driver = e2.driver
-			case DestroyEvent:
+			case system.DestroyEvent:
 				w.out <- e2
 				w.ack <- struct{}{}
 				return