app: prepare Window for removal of Main and asynchronous FrameEvents

This is mostly a refactor, but there are two user-visible effects:
- Window.NextEvent may be called even after DestroyEvent is returned.
- Window.Invalidate always wakes up a blocking NextEvent, even when a
FrameEvent cannot be generated.

As a nice side-effect, X11, Wayland and Wasm no longer require separate
goroutines for their window loops.

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

app/os_ios.go

@@ -81,10 +81,12 @@ import (
 	"unsafe"
 
 	"gioui.org/f32"
+	"gioui.org/io/event"
 	"gioui.org/io/key"
 	"gioui.org/io/pointer"
 	"gioui.org/io/system"
 	"gioui.org/io/transfer"
+	"gioui.org/op"
 	"gioui.org/unit"
 )
 
@@ -97,10 +99,11 @@ type window struct {
 	view        C.CFTypeRef
 	w           *callbacks
 	displayLink *displayLink
+	loop        *eventLoop
 
-	visible bool
-	cursor  pointer.Cursor
-	config  Config
+	hidden bool
+	cursor pointer.Cursor
+	config Config
 
 	pointerMap []C.CFTypeRef
 }
@@ -116,23 +119,26 @@ func init() {
 
 //export onCreate
 func onCreate(view, controller C.CFTypeRef) {
+	wopts := <-mainWindow.out
 	w := &window{
 		view: view,
+		w:    wopts.window,
 	}
+	w.loop = newEventLoop(w.w, w.wakeup)
+	w.w.SetDriver(w)
+	mainWindow.windows <- struct{}{}
 	dl, err := newDisplayLink(func() {
 		w.draw(false)
 	})
 	if err != nil {
-		panic(err)
+		w.w.ProcessEvent(DestroyEvent{Err: err})
+		return
 	}
 	w.displayLink = dl
-	wopts := <-mainWindow.out
-	w.w = wopts.window
-	w.w.SetDriver(w)
 	views[view] = w
 	w.Configure(wopts.options)
-	w.w.Event(StageEvent{Stage: StagePaused})
-	w.w.Event(ViewEvent{ViewController: uintptr(controller)})
+	w.ProcessEvent(StageEvent{Stage: StageRunning})
+	w.ProcessEvent(ViewEvent{ViewController: uintptr(controller)})
 }
 
 //export gio_onDraw
@@ -142,22 +148,20 @@ func gio_onDraw(view C.CFTypeRef) {
 }
 
 func (w *window) draw(sync bool) {
+	if w.hidden {
+		return
+	}
 	params := C.viewDrawParams(w.view)
 	if params.width == 0 || params.height == 0 {
 		return
 	}
-	wasVisible := w.visible
-	w.visible = true
-	if !wasVisible {
-		w.w.Event(StageEvent{Stage: StageRunning})
-	}
 	const inchPrDp = 1.0 / 163
 	m := unit.Metric{
 		PxPerDp: float32(params.dpi) * inchPrDp,
 		PxPerSp: float32(params.sdpi) * inchPrDp,
 	}
 	dppp := unit.Dp(1. / m.PxPerDp)
-	w.w.Event(frameEvent{
+	w.ProcessEvent(frameEvent{
 		FrameEvent: FrameEvent{
 			Now: time.Now(),
 			Size: image.Point{
@@ -179,24 +183,33 @@ func (w *window) draw(sync bool) {
 //export onStop
 func onStop(view C.CFTypeRef) {
 	w := views[view]
-	w.visible = false
-	w.w.Event(StageEvent{Stage: StagePaused})
+	w.hidden = true
+	w.ProcessEvent(StageEvent{Stage: StagePaused})
+}
+
+//export onStart
+func onStart(view C.CFTypeRef) {
+	w := views[view]
+	w.hidden = false
+	w.ProcessEvent(StageEvent{Stage: StageRunning})
+	w.draw(true)
 }
 
 //export onDestroy
 func onDestroy(view C.CFTypeRef) {
 	w := views[view]
-	delete(views, view)
-	w.w.Event(ViewEvent{})
-	w.w.Event(DestroyEvent{})
+	w.ProcessEvent(ViewEvent{})
+	w.ProcessEvent(DestroyEvent{})
 	w.displayLink.Close()
+	w.displayLink = nil
+	delete(views, view)
 	w.view = 0
 }
 
 //export onFocus
 func onFocus(view C.CFTypeRef, focus int) {
 	w := views[view]
-	w.w.Event(key.FocusEvent{Focus: focus != 0})
+	w.ProcessEvent(key.FocusEvent{Focus: focus != 0})
 }
 
 //export onLowMemory
@@ -254,7 +267,7 @@ func onTouch(last C.int, view, touchRef C.CFTypeRef, phase C.NSInteger, x, y C.C
 	w := views[view]
 	t := time.Duration(float64(ti) * float64(time.Second))
 	p := f32.Point{X: float32(x), Y: float32(y)}
-	w.w.Event(pointer.Event{
+	w.ProcessEvent(pointer.Event{
 		Kind:      kind,
 		Source:    pointer.Touch,
 		PointerID: w.lookupTouch(last != 0, touchRef),
@@ -267,7 +280,7 @@ func (w *window) ReadClipboard() {
 	cstr := C.readClipboard()
 	defer C.CFRelease(cstr)
 	content := nsstringToString(cstr)
-	w.w.Event(transfer.DataEvent{
+	w.ProcessEvent(transfer.DataEvent{
 		Type: "application/text",
 		Open: func() io.ReadCloser {
 			return io.NopCloser(strings.NewReader(content))
@@ -287,7 +300,7 @@ func (w *window) WriteClipboard(mime string, s []byte) {
 func (w *window) Configure([]Option) {
 	// Decorations are never disabled.
 	w.config.Decorated = true
-	w.w.Event(ConfigEvent{Config: w.config})
+	w.ProcessEvent(ConfigEvent{Config: w.config})
 }
 
 func (w *window) EditorStateChanged(old, new editorState) {}
@@ -295,10 +308,6 @@ func (w *window) EditorStateChanged(old, new editorState) {}
 func (w *window) Perform(system.Action) {}
 
 func (w *window) SetAnimating(anim bool) {
-	v := w.view
-	if v == 0 {
-		return
-	}
 	if anim {
 		w.displayLink.Start()
 	} else {
@@ -311,7 +320,7 @@ func (w *window) SetCursor(cursor pointer.Cursor) {
 }
 
 func (w *window) onKeyCommand(name key.Name) {
-	w.w.Event(key.Event{
+	w.ProcessEvent(key.Event{
 		Name: name,
 	})
 }
@@ -350,9 +359,30 @@ func (w *window) ShowTextInput(show bool) {
 
 func (w *window) SetInputHint(_ key.InputHint) {}
 
-func newWindow(win *callbacks, options []Option) error {
+func (w *window) ProcessEvent(e event.Event) {
+	w.w.ProcessEvent(e)
+	w.loop.FlushEvents()
+}
+
+func (w *window) Event() event.Event {
+	return w.loop.Event()
+}
+
+func (w *window) Invalidate() {
+	w.loop.Invalidate()
+}
+
+func (w *window) Run(f func()) {
+	w.loop.Run(f)
+}
+
+func (w *window) Frame(frame *op.Ops) {
+	w.loop.Frame(frame)
+}
+
+func newWindow(win *callbacks, options []Option) {
 	mainWindow.in <- windowAndConfig{win, options}
-	return <-mainWindow.errs
+	<-mainWindow.windows
 }
 
 func osMain() {