I forgot why I did it the other way lol (revert)

src/core/stack.rs

@@ -5,7 +5,7 @@ pub struct Stack {
 }
 
 impl<Ctx> Widget<Ctx> for Stack {
-    fn draw(&self, mut painter: Painter<Ctx>) {
+    fn draw(&self, painter: &mut Painter<Ctx>) {
         for child in &self.children {
             painter.draw(child);
         }