pub trait StateRenderer {
fn rect(&self) -> Rect;
fn render_child<W: Widget>(&mut self, w: W, rect: Rect);
fn render_child_stateful<W: StatefulWidget>(
&mut self,
w: W,
state: &mut W::State,
rect: Rect
);
fn render<W: Widget>(&mut self, w: W) { ... }
fn render_stateful<W: StatefulWidget>(&mut self, w: W, state: &mut W::State) { ... }
}