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/os_wayland.go

@@ -21,6 +21,7 @@ import (
 	"gioui.org/internal/fling"
 	"gioui.org/io/key"
 	"gioui.org/io/pointer"
+	"gioui.org/io/system"
 	syscall "golang.org/x/sys/unix"
 )
 
@@ -116,7 +117,7 @@ type window struct {
 		dir            f32.Point
 	}
 
-	stage             Stage
+	stage             system.Stage
 	dead              bool
 	pendingErr        error
 	lastFrameCallback *C.struct_wl_callback
@@ -302,7 +303,7 @@ func gio_onXdgSurfaceConfigure(data unsafe.Pointer, wmSurf *C.struct_xdg_surface
 	w.serial = serial
 	w.needAck = true
 	w.mu.Unlock()
-	w.setStage(StageRunning)
+	w.setStage(system.StageRunning)
 	w.draw(true)
 }
 
@@ -772,7 +773,7 @@ loop:
 			break
 		}
 		if w.dead {
-			w.w.event(DestroyEvent{Err: w.pendingErr})
+			w.w.event(system.DestroyEvent{Err: w.pendingErr})
 			break
 		}
 		// Clear poll events.
@@ -979,16 +980,16 @@ func (w *window) updateOutputs() {
 	}
 	w.mu.Unlock()
 	if !found {
-		w.setStage(StagePaused)
+		w.setStage(system.StagePaused)
 	} else {
-		w.setStage(StageRunning)
+		w.setStage(system.StageRunning)
 		w.draw(true)
 	}
 }
 
-func (w *window) config() (int, int, Config) {
+func (w *window) config() (int, int, config) {
 	width, height := w.width*w.scale, w.height*w.scale
-	return width, height, Config{
+	return width, height, config{
 		pxPerDp: w.ppdp * float32(w.scale),
 		pxPerSp: w.ppsp * float32(w.scale),
 	}
@@ -1015,7 +1016,7 @@ func (w *window) draw(sync bool) {
 		return
 	}
 	width, height, cfg := w.config()
-	if cfg == (Config{}) {
+	if cfg == (config{}) {
 		return
 	}
 	if animating && w.lastFrameCallback == nil {
@@ -1024,22 +1025,24 @@ func (w *window) draw(sync bool) {
 		C.gio_wl_callback_add_listener(w.lastFrameCallback, unsafe.Pointer(w.surf))
 	}
 	cfg.now = time.Now()
-	w.w.event(FrameEvent{
-		Size: image.Point{
-			X: width,
-			Y: height,
+	w.w.event(frameEvent{
+		FrameEvent: system.FrameEvent{
+			Size: image.Point{
+				X: width,
+				Y: height,
+			},
+			Config: &cfg,
 		},
-		Config: cfg,
-		sync:   sync,
+		sync: sync,
 	})
 }
 
-func (w *window) setStage(s Stage) {
+func (w *window) setStage(s system.Stage) {
 	if s == w.stage {
 		return
 	}
 	w.stage = s
-	w.w.event(StageEvent{s})
+	w.w.event(system.StageEvent{s})
 }
 
 func (w *window) display() *C.struct_wl_display {