I have a SingleChildScrollView, and it can scrolls horizontally. The child widget of the SingleChildScrollView is a Container widget with height: 125.0, width: 3000.0
the child widget of the Container is a Stack widget with children are all Draggable widgets wrapped by Positioned widget, so I can place these Draggable widgets at my will. But when I use RenderRepaintBoundary toImage() method to capture the content of ScrollView, only the visible area can be captured, not the full content of ScrollView.