ui/app: create windows directly

Replace CreateWindow with NewWindow that immediately creates a Window
ready to use.

Drop the Windows channel of windows created by the system. For iOS
and Android where the system creates the windows, let them rendezvous
with the window created in the first NewWindow call.

Android is further changed so that destroying and re-creating the
Java Activity simply reconnects with the original Window.

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

ui/app/app.go

@@ -3,6 +3,7 @@
 package app
 
 import (
+	"errors"
 	"image"
 	"math"
 	"os"
@@ -47,6 +48,17 @@ type CommandEvent struct {
 type Stage uint8
 type CommandType uint8
 
+type windowRendezvous struct {
+	in   chan windowAndOptions
+	out  chan windowAndOptions
+	errs chan error
+}
+
+type windowAndOptions struct {
+	window *Window
+	opts   *WindowOptions
+}
+
 const (
 	StageDead Stage = iota
 	StagePaused
@@ -79,30 +91,6 @@ const (
 // Set with the go linker flag -X.
 var extraArgs string
 
-var windows = make(chan *Window)
-
-// CreateWindow creates a new window for a set of window
-// options. The options are hints; the platform is free to
-// ignore or adjust them.
-// CreateWindow is not supported on iOS and Android.
-func CreateWindow(opts *WindowOptions) error {
-	if opts == nil {
-		opts = &WindowOptions{
-			Width:  ui.Dp(800),
-			Height: ui.Dp(600),
-			Title:  "Gio program",
-		}
-	}
-	if opts.Width.V <= 0 || opts.Height.V <= 0 {
-		panic("window width and height must be larger than 0")
-	}
-	return createWindow(opts)
-}
-
-func Windows() <-chan *Window {
-	return windows
-}
-
 func (l Stage) String() string {
 	switch l {
 	case StageDead:
@@ -164,3 +152,29 @@ func (c *Config) Px(v ui.Value) int {
 	}
 	return int(math.Round(float64(r)))
 }
+
+func newWindowRendezvous() *windowRendezvous {
+	wr := &windowRendezvous{
+		in:   make(chan windowAndOptions),
+		out:  make(chan windowAndOptions),
+		errs: make(chan error),
+	}
+	go func() {
+		var main windowAndOptions
+		var out chan windowAndOptions
+		for {
+			select {
+			case w := <-wr.in:
+				var err error
+				if main.window != nil {
+					err = errors.New("multiple windows are not supported")
+				}
+				wr.errs <- err
+				main = w
+				out = wr.out
+			case out <- main:
+			}
+		}
+	}()
+	return wr
+}

ui/app/os_android.go

@@ -58,6 +58,8 @@ var theJVM *C.JavaVM
 
 var views = make(map[C.jlong]*window)
 
+var mainWindow = newWindowRendezvous()
+
 func jniGetMethodID(env *C.JNIEnv, class C.jclass, method, sig string) C.jmethodID {
 	m := C.CString(method)
 	defer C.free(unsafe.Pointer(m))
@@ -91,12 +93,12 @@ func onCreateView(env *C.JNIEnv, class C.jclass, view C.jobject) C.jlong {
 		mpostFrameCallback:             jniGetMethodID(env, class, "postFrameCallback", "()V"),
 		mpostFrameCallbackOnMainThread: jniGetMethodID(env, class, "postFrameCallbackOnMainThread", "()V"),
 	}
-	ow := newWindow(w)
+	wopts := <-mainWindow.out
-	w.Window = ow
+	w.Window = wopts.window
+	w.Window.setDriver(w)
 	handle := C.jlong(view)
 	views[handle] = w
 	w.loadConfig(env, class)
-	windows <- ow
 	w.setStage(StagePaused)
 	return handle
 }
@@ -104,8 +106,8 @@ func onCreateView(env *C.JNIEnv, class C.jclass, view C.jobject) C.jlong {
 //export onDestroyView
 func onDestroyView(env *C.JNIEnv, class C.jclass, handle C.jlong) {
 	w := views[handle]
+	w.setDriver(nil)
 	delete(views, handle)
-	w.setStage(StageDead)
 	C.gio_jni_DeleteGlobalRef(env, w.view)
 	w.view = 0
 }
@@ -408,10 +410,11 @@ func (w *window) setTextInput(s key.TextInputState) {
 }
 
 func Main() {
-	// Android runs in c-shared mode where is never reached.
+	// Android runs in c-shared mode where main is never reached.
-	panic("unreachable")
+	panic("call to Main from outside main")
 }
 
-func createWindow(opts *WindowOptions) error {
+func createWindow(window *Window, opts *WindowOptions) error {
-	return errors.New("createWindow not supported")
+	mainWindow.in <- windowAndOptions{window, opts}
+	return <-mainWindow.errs
 }

ui/app/os_ios.go

@@ -38,6 +38,8 @@ type window struct {
 	pointerMap []C.CFTypeRef
 }
 
+var mainWindow = newWindowRendezvous()
+
 var layerFactory func() uintptr
 
 var views = make(map[C.CFTypeRef]*window)
@@ -52,13 +54,13 @@ func onCreate(view C.CFTypeRef) {
 	w := &window{
 		view: view,
 	}
-	ow := newWindow(w)
+	wopts := <-mainWindow.out
-	w.w = ow
+	w.w = wopts.window
+	w.w.setDriver(w)
 	w.visible.Store(false)
 	w.layer = C.CFTypeRef(layerFactory())
 	C.gio_addLayerToView(view, w.layer)
 	views[view] = w
-	windows <- ow
 	w.w.event(StageEvent{StagePaused})
 }
 
@@ -245,11 +247,12 @@ func (w *window) setTextInput(s key.TextInputState) {
 	}
 }
 
-func createWindow(opts *WindowOptions) error {
+func createWindow(win *Window, opts *WindowOptions) error {
-	panic("unsupported")
+	mainWindow.in <- windowAndOptions{win, opts}
+	return <-mainWindow.errs
 }
 
 func Main() {
 	// iOS runs in c-archive mode, so this is never reached.
-	panic("unreachable")
+	panic("call to Main from outside main")
 }

ui/app/os_js.go

@@ -31,7 +31,7 @@ type window struct {
 
 var mainDone = make(chan struct{})
 
-func createWindow(opts *WindowOptions) error {
+func createWindow(win *Window, opts *WindowOptions) error {
 	doc := js.Global().Get("document")
 	parent := doc.Call("getElementById", "giowindow")
 	if parent == js.Null() {
@@ -52,9 +52,9 @@ func createWindow(opts *WindowOptions) error {
 		return nil
 	})
 	w.addEventListeners()
-	w.w = newWindow(w)
+	w.w = win
 	go func() {
-		windows <- w.w
+		w.w.setDriver(w)
 		w.focus()
 		w.w.event(StageEvent{StageRunning})
 		w.draw(true)

ui/app/os_macos.go

@@ -15,7 +15,6 @@ import (
 	"errors"
 	"image"
 	"runtime"
-	"sync"
 	"time"
 	"unsafe"
 
@@ -35,12 +34,7 @@ type window struct {
 	stage Stage
 }
 
-// Only support one main window for now.
+var mainWindow = newWindowRendezvous()
-var singleWindow struct {
-	mu      sync.Mutex
-	hasOpts bool
-	opts    *WindowOptions
-}
 
 var viewFactory func() C.CFTypeRef
 
@@ -170,7 +164,6 @@ func gio_onTerminate(view C.CFTypeRef) {
 	w := views[view]
 	delete(views, view)
 	w.setStage(StageDead)
-	close(windows)
 }
 
 //export gio_onHide
@@ -190,31 +183,26 @@ func gio_onCreate(view C.CFTypeRef) {
 	w := &window{
 		view: view,
 	}
-	ow := newWindow(w)
+	wopts := <-mainWindow.out
-	w.w = ow
+	w.w = wopts.window
+	w.w.setDriver(w)
 	views[view] = w
-	windows <- ow
 }
 
-func createWindow(opts *WindowOptions) error {
+func createWindow(win *Window, opts *WindowOptions) error {
-	singleWindow.mu.Lock()
+	mainWindow.in <- windowAndOptions{win, opts}
-	defer singleWindow.mu.Unlock()
+	return <-mainWindow.errs
-	if singleWindow.hasOpts {
-		panic("only one window supported")
-	}
-	singleWindow.opts = opts
-	singleWindow.hasOpts = true
-	return nil
 }
 
 func Main() {
+	wopts := <-mainWindow.out
 	view := viewFactory()
 	if view == 0 {
 		// TODO: return this error from CreateWindow.
 		panic(errors.New("CreateWindow: failed to create view"))
 	}
 	cfg := getConfig()
-	opts := singleWindow.opts
+	opts := wopts.opts
 	w := cfg.Px(opts.Width)
 	h := cfg.Px(opts.Height)
 	title := C.CString(opts.Title)

ui/app/os_wayland.go

@@ -155,11 +155,11 @@ func Main() {
 	<-mainDone
 }
 
-func createWindow(opts *WindowOptions) error {
+func createWindow(window *Window, opts *WindowOptions) error {
 	connMu.Lock()
 	defer connMu.Unlock()
 	if len(winMap) > 0 {
-		panic("multiple windows are not supported")
+		return errors.New("multiple windows are not supported")
 	}
 	if err := waylandConnect(); err != nil {
 		return err
@@ -169,13 +169,13 @@ func createWindow(opts *WindowOptions) error {
 		conn.destroy()
 		return err
 	}
+	w.w = window
 	go func() {
-		windows <- w.w
+		w.w.setDriver(w)
 		w.setStage(StageRunning)
 		w.loop()
 		w.destroy()
 		conn.destroy()
-		close(windows)
 		close(mainDone)
 	}()
 	return nil
@@ -250,8 +250,6 @@ func createNativeWindow(opts *WindowOptions) (*window, error) {
 	}
 	w.updateOpaqueRegion()
 	C.wl_surface_commit(w.surf)
-	ow := newWindow(w)
-	w.w = ow
 	winMap[w.topLvl] = w
 	winMap[w.surf] = w
 	winMap[w.wmSurf] = w

ui/app/os_windows.go

@@ -3,6 +3,7 @@
 package app
 
 import (
+	"errors"
 	"fmt"
 	"image"
 	"runtime"
@@ -159,11 +160,11 @@ func Main() {
 	<-mainDone
 }
 
-func createWindow(opts *WindowOptions) error {
+func createWindow(window *Window, opts *WindowOptions) error {
 	onceMu.Lock()
 	defer onceMu.Unlock()
 	if len(winMap) > 0 {
-		panic("multiple windows are not supported")
+		return errors.New("multiple windows are not supported")
 	}
 	cerr := make(chan error)
 	go func() {
@@ -176,14 +177,14 @@ func createWindow(opts *WindowOptions) error {
 		}
 		defer w.destroy()
 		cerr <- nil
-		windows <- w.w
+		w.w = window
+		w.w.setDriver(w)
 		showWindow(w.hwnd, _SW_SHOWDEFAULT)
 		setForegroundWindow(w.hwnd)
 		setFocus(w.hwnd)
 		if err := w.loop(); err != nil {
 			panic(err)
 		}
-		close(windows)
 		close(mainDone)
 	}()
 	return <-cerr
@@ -248,7 +249,6 @@ func createNativeWindow(opts *WindowOptions) (*window, error) {
 	if err != nil {
 		return nil, err
 	}
-	w.w = newWindow(w)
 	return w, nil
 }
 

ui/app/window.go

@@ -13,8 +13,8 @@ import (
 	"gioui.org/ui/app/internal/gpu"
 	iinput "gioui.org/ui/app/internal/input"
 	"gioui.org/ui/input"
-	"gioui.org/ui/system"
 	"gioui.org/ui/key"
+	"gioui.org/ui/system"
 )
 
 type WindowOptions struct {
@@ -47,6 +47,12 @@ type Window struct {
 	router iinput.Router
 }
 
+// driverEvent is sent when a new native driver
+// is available for the Window.
+type driverEvent struct {
+	driver *window
+}
+
 // driver is the interface for the platform implementation
 // of a Window.
 var _ interface {
@@ -59,13 +65,31 @@ var _ interface {
 
 var ackEvent Event
 
-func newWindow(nw *window) *Window {
+// NewWindow creates a new window for a set of window
+// options. The options are hints; the platform is free to
+// ignore or adjust them.
+// If the current program is running on iOS and Android,
+// NewWindow returns the window previously by the platform.
+func NewWindow(opts *WindowOptions) (*Window, error) {
+	if opts == nil {
+		opts = &WindowOptions{
+			Width:  ui.Dp(800),
+			Height: ui.Dp(600),
+			Title:  "Gio program",
+		}
+	}
+	if opts.Width.V <= 0 || opts.Height.V <= 0 {
+		panic("window width and height must be larger than 0")
+	}
+
 	w := &Window{
-		driver: nw,
 		events: make(chan Event),
 		stage:  StagePaused,
 	}
-	return w
+	if err := createWindow(w, opts); err != nil {
+		return nil, err
+	}
+	return w, nil
 }
 
 func (w *Window) Events() <-chan Event {
@@ -103,8 +127,9 @@ func (w *Window) Draw(root *ui.Ops) {
 	w.syncGPU = false
 	alive := w.isAlive()
 	size := w.size
+	driver := w.driver
 	w.mu.Unlock()
-	if !alive || stage < StageRunning {
+	if !alive || stage < StageRunning || driver == nil {
 		return
 	}
 	if w.gpu != nil {
@@ -117,7 +142,7 @@ func (w *Window) Draw(root *ui.Ops) {
 		}
 	}
 	if w.gpu == nil {
-		ctx, err := newContext(w.driver)
+		ctx, err := newContext(driver)
 		if err != nil {
 			w.err = err
 			return
@@ -205,6 +230,12 @@ func (w *Window) contextDriver() interface{} {
 	return w.driver
 }
 
+func (w *Window) setDriver(d *window) {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+	w.driver = d
+}
+
 func (w *Window) event(e Event) {
 	w.eventLock.Lock()
 	defer w.eventLock.Unlock()