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/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)
-	w.Window = ow
+	wopts := <-mainWindow.out
+	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.
-	panic("unreachable")
+	// Android runs in c-shared mode where main is never reached.
+	panic("call to Main from outside main")
 }
 
-func createWindow(opts *WindowOptions) error {
-	return errors.New("createWindow not supported")
+func createWindow(window *Window, opts *WindowOptions) error {
+	mainWindow.in <- windowAndOptions{window, opts}
+	return <-mainWindow.errs
 }