mobile/ebitenmobileview: Allow Layout without SetGame

mobile/ebitenmobileview/funcs.go

@@ -30,9 +30,16 @@ type ViewRectSetter interface {
 func Layout(viewWidth, viewHeight int, viewRectSetter ViewRectSetter) {
 	theState.m.Lock()
 	defer theState.m.Unlock()
+	layout(viewWidth, viewHeight, viewRectSetter)
+}
 
+func layout(viewWidth, viewHeight int, viewRectSetter ViewRectSetter) {
 	if theState.game == nil {
-		panic("ebitenmobileview: SetGame must be called before Layout")
+		// It is fine to override the existing function since only the last layout result matters.
+		theState.delayedLayout = func() {
+			layout(viewWidth, viewHeight, viewRectSetter)
+		}
+		return
 	}
 
 	w, h := theState.game.Layout(int(viewWidth), int(viewHeight))

mobile/ebitenmobileview/game.go

@@ -34,6 +34,8 @@ type state struct {
 
 	running bool
 
+	delayedLayout func()
+
 	// m is a mutex required for each function.
 	// For example, on Android, Update can be called from a different thread:
 	// https://developer.android.com/reference/android/opengl/GLSurfaceView.Renderer
@@ -45,4 +47,9 @@ func SetGame(game game) {
 	defer theState.m.Unlock()
 
 	theState.game = game
+
+	if theState.delayedLayout != nil {
+		theState.delayedLayout()
+		theState.delayedLayout = nil
+	}
 }