Make widget::Tree mutable in Widget::layout

core/src/element.rs

@@ -306,7 +306,7 @@ where
 
     fn layout(
         &self,
-        tree: &Tree,
+        tree: &mut Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {
@@ -492,7 +492,7 @@ where
 
     fn layout(
         &self,
-        tree: &Tree,
+        tree: &mut Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {

core/src/layout/flex.rs

@@ -67,7 +67,7 @@ pub fn resolve<Message, Renderer>(
     spacing: f32,
     align_items: Alignment,
     items: &[Element<'_, Message, Renderer>],
-    trees: &[widget::Tree],
+    trees: &mut [widget::Tree],
 ) -> Node
 where
     Renderer: crate::Renderer,
@@ -83,7 +83,7 @@ where
     let mut nodes: Vec<Node> = Vec::with_capacity(items.len());
     nodes.resize(items.len(), Node::default());
 
-    for (i, (child, tree)) in items.iter().zip(trees).enumerate() {
+    for (i, (child, tree)) in items.iter().zip(trees.iter_mut()).enumerate() {
         let fill_factor = match axis {
             Axis::Horizontal => child.as_widget().width(),
             Axis::Vertical => child.as_widget().height(),

core/src/overlay.rs

@@ -25,7 +25,7 @@ where
     ///
     /// [`Node`]: layout::Node
     fn layout(
-        &self,
+        &mut self,
         renderer: &Renderer,
         bounds: Size,
         position: Point,

core/src/overlay/element.rs

@@ -54,7 +54,7 @@ where
 
     /// Computes the layout of the [`Element`] in the given bounds.
     pub fn layout(
-        &self,
+        &mut self,
         renderer: &Renderer,
         bounds: Size,
         translation: Vector,
@@ -150,7 +150,7 @@ where
     Renderer: crate::Renderer,
 {
     fn layout(
-        &self,
+        &mut self,
         renderer: &Renderer,
         bounds: Size,
         position: Point,

core/src/overlay/group.rs

@@ -61,7 +61,7 @@ where
     Renderer: crate::Renderer,
 {
     fn layout(
-        &self,
+        &mut self,
         renderer: &Renderer,
         bounds: Size,
         position: Point,
@@ -71,7 +71,7 @@ where
         layout::Node::with_children(
             bounds,
             self.children
-                .iter()
+                .iter_mut()
                 .map(|child| child.layout(renderer, bounds, translation))
                 .collect(),
         )

core/src/widget.rs

@@ -55,7 +55,7 @@ where
     /// user interface.
     fn layout(
         &self,
-        tree: &Tree,
+        tree: &mut Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node;

core/src/widget/text.rs

@@ -3,12 +3,11 @@ use crate::alignment;
 use crate::layout;
 use crate::mouse;
 use crate::renderer;
-use crate::text::{self, Paragraph as _};
+use crate::text::{self, Paragraph};
 use crate::widget::tree::{self, Tree};
 use crate::{Color, Element, Layout, Length, Pixels, Point, Rectangle, Widget};
 
 use std::borrow::Cow;
-use std::cell::RefCell;
 
 pub use text::{LineHeight, Shaping};
 
@@ -120,7 +119,7 @@ where
 
 /// The internal state of a [`Text`] widget.
 #[derive(Debug, Default)]
-pub struct State<T>(RefCell<T>);
+pub struct State<P: Paragraph>(P);
 
 impl<'a, Message, Renderer> Widget<Message, Renderer> for Text<'a, Renderer>
 where
@@ -132,7 +131,7 @@ where
     }
 
     fn state(&self) -> tree::State {
-        tree::State::new(State(RefCell::new(Renderer::Paragraph::default())))
+        tree::State::new(State(Renderer::Paragraph::default()))
     }
 
     fn width(&self) -> Length {
@@ -145,12 +144,12 @@ where
 
     fn layout(
         &self,
-        tree: &Tree,
+        tree: &mut Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {
         layout(
-            tree.state.downcast_ref::<State<Renderer::Paragraph>>(),
+            tree.state.downcast_mut::<State<Renderer::Paragraph>>(),
             renderer,
             limits,
             self.width,
@@ -189,7 +188,7 @@ where
 
 /// Produces the [`layout::Node`] of a [`Text`] widget.
 pub fn layout<Renderer>(
-    state: &State<Renderer::Paragraph>,
+    state: &mut State<Renderer::Paragraph>,
     renderer: &Renderer,
     limits: &layout::Limits,
     width: Length,
@@ -211,10 +210,10 @@ where
     let size = size.unwrap_or_else(|| renderer.default_size());
     let font = font.unwrap_or_else(|| renderer.default_font());
 
-    let mut paragraph = state.0.borrow_mut();
+    let State(ref mut paragraph) = state;
 
     renderer.update_paragraph(
-        &mut paragraph,
+        paragraph,
         text::Text {
             content,
             bounds,
@@ -251,7 +250,7 @@ pub fn draw<Renderer>(
 ) where
     Renderer: text::Renderer,
 {
-    let paragraph = state.0.borrow();
+    let State(ref paragraph) = state;
     let bounds = layout.bounds();
 
     let x = match paragraph.horizontal_alignment() {

examples/custom_quad/src/main.rs

@@ -36,7 +36,7 @@ mod quad {
 
         fn layout(
             &self,
-            _tree: &widget::Tree,
+            _tree: &mut widget::Tree,
             _renderer: &Renderer,
             _limits: &layout::Limits,
         ) -> layout::Node {

examples/custom_widget/src/main.rs

@@ -43,7 +43,7 @@ mod circle {
 
         fn layout(
             &self,
-            _tree: &widget::Tree,
+            _tree: &mut widget::Tree,
             _renderer: &Renderer,
             _limits: &layout::Limits,
         ) -> layout::Node {

examples/geometry/src/main.rs

@@ -26,7 +26,7 @@ mod rainbow {
 
         fn layout(
             &self,
-            _tree: &widget::Tree,
+            _tree: &mut widget::Tree,
             _renderer: &Renderer,
             limits: &layout::Limits,
         ) -> layout::Node {

examples/loading_spinners/src/circular.rs

@@ -254,7 +254,7 @@ where
 
     fn layout(
         &self,
-        _tree: &Tree,
+        _tree: &mut Tree,
         _renderer: &iced::Renderer<Theme>,
         limits: &layout::Limits,
     ) -> layout::Node {

examples/loading_spinners/src/linear.rs

@@ -175,7 +175,7 @@ where
 
     fn layout(
         &self,
-        _tree: &Tree,
+        _tree: &mut Tree,
         _renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {

examples/modal/src/main.rs

@@ -285,13 +285,15 @@ mod modal {
 
         fn layout(
             &self,
-            tree: &widget::Tree,
+            tree: &mut widget::Tree,
             renderer: &Renderer,
             limits: &layout::Limits,
         ) -> layout::Node {
-            self.base
+            self.base.as_widget().layout(
-                .as_widget()
+                &mut tree.children[0],
-                .layout(&tree.children[0], renderer, limits)
+                renderer,
+                limits,
+            )
         }
 
         fn on_event(
@@ -402,7 +404,7 @@ mod modal {
         Message: Clone,
     {
         fn layout(
-            &self,
+            &mut self,
             renderer: &Renderer,
             _bounds: Size,
             position: Point,

examples/toast/src/main.rs

@@ -326,13 +326,15 @@ mod toast {
 
         fn layout(
             &self,
-            tree: &Tree,
+            tree: &mut Tree,
             renderer: &Renderer,
             limits: &layout::Limits,
         ) -> layout::Node {
-            self.content
+            self.content.as_widget().layout(
-                .as_widget()
+                &mut tree.children[0],
-                .layout(&tree.children[0], renderer, limits)
+                renderer,
+                limits,
+            )
         }
 
         fn tag(&self) -> widget::tree::Tag {
@@ -503,7 +505,7 @@ mod toast {
         for Overlay<'a, 'b, Message>
     {
         fn layout(
-            &self,
+            &mut self,
             renderer: &Renderer,
             bounds: Size,
             position: Point,

runtime/src/user_interface.rs

@@ -96,7 +96,7 @@ where
         state.diff(root.as_widget());
 
         let base = root.as_widget().layout(
-            &state,
+            &mut state,
             renderer,
             &layout::Limits::new(Size::ZERO, bounds),
         );
@@ -230,7 +230,7 @@ where
                     let _ = ManuallyDrop::into_inner(manual_overlay);
 
                     self.base = self.root.as_widget().layout(
-                        &self.state,
+                        &mut self.state,
                         renderer,
                         &layout::Limits::new(Size::ZERO, self.bounds),
                     );
@@ -330,7 +330,7 @@ where
 
                 shell.revalidate_layout(|| {
                     self.base = self.root.as_widget().layout(
-                        &self.state,
+                        &mut self.state,
                         renderer,
                         &layout::Limits::new(Size::ZERO, self.bounds),
                     );

widget/src/button.rs

@@ -159,14 +159,16 @@ where
 
     fn layout(
         &self,
-        tree: &Tree,
+        tree: &mut Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {
         layout(limits, self.width, self.height, self.padding, |limits| {
-            self.content
+            self.content.as_widget().layout(
-                .as_widget()
+                &mut tree.children[0],
-                .layout(&tree.children[0], renderer, limits)
+                renderer,
+                limits,
+            )
         })
     }
 

widget/src/canvas.rs

@@ -129,7 +129,7 @@ where
 
     fn layout(
         &self,
-        _tree: &Tree,
+        _tree: &mut Tree,
         _renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {

widget/src/checkbox.rs

@@ -184,7 +184,7 @@ where
 
     fn layout(
         &self,
-        tree: &Tree,
+        tree: &mut Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {
@@ -195,7 +195,7 @@ where
             |limits| {
                 let state = tree
                     .state
-                    .downcast_ref::<widget::text::State<Renderer::Paragraph>>();
+                    .downcast_mut::<widget::text::State<Renderer::Paragraph>>();
 
                 widget::text::layout(
                     state,

widget/src/column.rs

@@ -122,7 +122,7 @@ where
 
     fn layout(
         &self,
-        tree: &Tree,
+        tree: &mut Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {
@@ -139,7 +139,7 @@ where
             self.spacing,
             self.align_items,
             &self.children,
-            &tree.children,
+            &mut tree.children,
         )
     }
 

widget/src/combo_box.rs

@@ -305,7 +305,7 @@ where
 
     fn layout(
         &self,
-        tree: &widget::Tree,
+        tree: &mut widget::Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {

widget/src/container.rs

@@ -162,7 +162,7 @@ where
 
     fn layout(
         &self,
-        tree: &Tree,
+        tree: &mut Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {

widget/src/image.rs

@@ -167,7 +167,7 @@ where
 
     fn layout(
         &self,
-        _tree: &Tree,
+        _tree: &mut Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {

widget/src/image/viewer.rs

@@ -105,7 +105,7 @@ where
 
     fn layout(
         &self,
-        _tree: &Tree,
+        _tree: &mut Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {

widget/src/lazy.rs

@@ -152,7 +152,7 @@ where
 
     fn layout(
         &self,
-        tree: &Tree,
+        tree: &mut Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {
@@ -327,7 +327,7 @@ where
     Renderer: core::Renderer,
 {
     fn layout(
-        &self,
+        &mut self,
         renderer: &Renderer,
         bounds: Size,
         position: Point,

widget/src/lazy/component.rs

@@ -254,7 +254,7 @@ where
 
     fn layout(
         &self,
-        tree: &Tree,
+        tree: &mut Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {
@@ -567,7 +567,7 @@ where
     S: 'static + Default,
 {
     fn layout(
-        &self,
+        &mut self,
         renderer: &Renderer,
         bounds: Size,
         position: Point,

widget/src/lazy/responsive.rs

@@ -60,7 +60,7 @@ impl<'a, Message, Renderer> Content<'a, Message, Renderer>
 where
     Renderer: core::Renderer,
 {
-    fn layout(&mut self, tree: &Tree, renderer: &Renderer) {
+    fn layout(&mut self, tree: &mut Tree, renderer: &Renderer) {
         if self.layout.is_none() {
             self.layout = Some(self.element.as_widget().layout(
                 tree,
@@ -144,7 +144,7 @@ where
 
     fn layout(
         &self,
-        _tree: &Tree,
+        _tree: &mut Tree,
         _renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {
@@ -363,7 +363,7 @@ where
     Renderer: core::Renderer,
 {
     fn layout(
-        &self,
+        &mut self,
         renderer: &Renderer,
         bounds: Size,
         position: Point,

widget/src/mouse_area.rs

@@ -120,7 +120,7 @@ where
 
     fn layout(
         &self,
-        tree: &Tree,
+        tree: &mut Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {

widget/src/overlay/menu.rs

@@ -232,7 +232,7 @@ where
     Renderer::Theme: StyleSheet + container::StyleSheet,
 {
     fn layout(
-        &self,
+        &mut self,
         renderer: &Renderer,
         bounds: Size,
         position: Point,
@@ -352,7 +352,7 @@ where
 
     fn layout(
         &self,
-        _tree: &Tree,
+        _tree: &mut Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {

widget/src/pane_grid.rs

@@ -275,7 +275,7 @@ where
 
     fn layout(
         &self,
-        tree: &Tree,
+        tree: &mut Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {
@@ -475,7 +475,7 @@ where
 
 /// Calculates the [`Layout`] of a [`PaneGrid`].
 pub fn layout<Renderer, T>(
-    tree: &Tree,
+    tree: &mut Tree,
     renderer: &Renderer,
     limits: &layout::Limits,
     node: &Node,
@@ -483,14 +483,19 @@ pub fn layout<Renderer, T>(
     height: Length,
     spacing: f32,
     contents: impl Iterator<Item = (Pane, T)>,
-    layout_content: impl Fn(T, &Tree, &Renderer, &layout::Limits) -> layout::Node,
+    layout_content: impl Fn(
+        T,
+        &mut Tree,
+        &Renderer,
+        &layout::Limits,
+    ) -> layout::Node,
 ) -> layout::Node {
     let limits = limits.width(width).height(height);
     let size = limits.resolve(Size::ZERO);
 
     let regions = node.pane_regions(spacing, size);
     let children = contents
-        .zip(tree.children.iter())
+        .zip(tree.children.iter_mut())
         .filter_map(|((pane, content), tree)| {
             let region = regions.get(&pane)?;
             let size = Size::new(region.width, region.height);

widget/src/pane_grid/content.rs

@@ -150,7 +150,7 @@ where
 
     pub(crate) fn layout(
         &self,
-        tree: &Tree,
+        tree: &mut Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {
@@ -158,7 +158,7 @@ where
             let max_size = limits.max();
 
             let title_bar_layout = title_bar.layout(
-                &tree.children[1],
+                &mut tree.children[1],
                 renderer,
                 &layout::Limits::new(Size::ZERO, max_size),
             );
@@ -166,7 +166,7 @@ where
             let title_bar_size = title_bar_layout.size();
 
             let mut body_layout = self.body.as_widget().layout(
-                &tree.children[0],
+                &mut tree.children[0],
                 renderer,
                 &layout::Limits::new(
                     Size::ZERO,
@@ -184,9 +184,11 @@ where
                 vec![title_bar_layout, body_layout],
             )
         } else {
-            self.body
+            self.body.as_widget().layout(
-                .as_widget()
+                &mut tree.children[0],
-                .layout(&tree.children[0], renderer, limits)
+                renderer,
+                limits,
+            )
         }
     }
 

widget/src/pane_grid/title_bar.rs

@@ -213,7 +213,7 @@ where
 
     pub(crate) fn layout(
         &self,
-        tree: &Tree,
+        tree: &mut Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {
@@ -221,7 +221,7 @@ where
         let max_size = limits.max();
 
         let title_layout = self.content.as_widget().layout(
-            &tree.children[0],
+            &mut tree.children[0],
             renderer,
             &layout::Limits::new(Size::ZERO, max_size),
         );
@@ -230,7 +230,7 @@ where
 
         let mut node = if let Some(controls) = &self.controls {
             let mut controls_layout = controls.as_widget().layout(
-                &tree.children[1],
+                &mut tree.children[1],
                 renderer,
                 &layout::Limits::new(Size::ZERO, max_size),
             );

widget/src/pick_list.rs

@@ -18,7 +18,6 @@ use crate::overlay::menu::{self, Menu};
 use crate::scrollable;
 
 use std::borrow::Cow;
-use std::cell::RefCell;
 
 pub use crate::style::pick_list::{Appearance, StyleSheet};
 
@@ -175,12 +174,12 @@ where
 
     fn layout(
         &self,
-        tree: &Tree,
+        tree: &mut Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {
         layout(
-            tree.state.downcast_ref::<State<Renderer::Paragraph>>(),
+            tree.state.downcast_mut::<State<Renderer::Paragraph>>(),
             renderer,
             limits,
             self.width,
@@ -305,8 +304,8 @@ pub struct State<P: text::Paragraph> {
     keyboard_modifiers: keyboard::Modifiers,
     is_open: bool,
     hovered_option: Option<usize>,
-    option_paragraphs: RefCell<Vec<P>>,
+    options: Vec<P>,
-    placeholder_paragraph: RefCell<P>,
+    placeholder: P,
 }
 
 impl<P: text::Paragraph> State<P> {
@@ -317,8 +316,8 @@ impl<P: text::Paragraph> State<P> {
             keyboard_modifiers: keyboard::Modifiers::default(),
             is_open: bool::default(),
             hovered_option: Option::default(),
-            option_paragraphs: RefCell::new(Vec::new()),
+            options: Vec::new(),
-            placeholder_paragraph: RefCell::new(Default::default()),
+            placeholder: P::default(),
         }
     }
 }
@@ -375,7 +374,7 @@ pub struct Icon<Font> {
 
 /// Computes the layout of a [`PickList`].
 pub fn layout<Renderer, T>(
-    state: &State<Renderer::Paragraph>,
+    state: &mut State<Renderer::Paragraph>,
     renderer: &Renderer,
     limits: &layout::Limits,
     width: Length,
@@ -397,9 +396,7 @@ where
     let font = font.unwrap_or_else(|| renderer.default_font());
     let text_size = text_size.unwrap_or_else(|| renderer.default_size());
 
-    let mut paragraphs = state.option_paragraphs.borrow_mut();
+    state.options.resize_with(options.len(), Default::default);
-
-    paragraphs.resize_with(options.len(), Default::default);
 
     let option_text = Text {
         content: "",
@@ -415,7 +412,7 @@ where
         shaping: text_shaping,
     };
 
-    for (option, paragraph) in options.iter().zip(paragraphs.iter_mut()) {
+    for (option, paragraph) in options.iter().zip(state.options.iter_mut()) {
         let label = option.to_string();
 
         renderer.update_paragraph(
@@ -428,9 +425,8 @@ where
     }
 
     if let Some(placeholder) = placeholder {
-        let mut paragraph = state.placeholder_paragraph.borrow_mut();
         renderer.update_paragraph(
-            &mut paragraph,
+            &mut state.placeholder,
             Text {
                 content: placeholder,
                 ..option_text
@@ -441,13 +437,13 @@ where
     let max_width = match width {
         Length::Shrink => {
             let labels_width =
-                paragraphs.iter().fold(0.0, |width, paragraph| {
+                state.options.iter().fold(0.0, |width, paragraph| {
                     f32::max(width, paragraph.min_width())
                 });
 
             labels_width.max(
                 placeholder
-                    .map(|_| state.placeholder_paragraph.borrow().min_width())
+                    .map(|_| state.placeholder.min_width())
                     .unwrap_or(0.0),
             )
         }

widget/src/progress_bar.rs

@@ -95,7 +95,7 @@ where
 
     fn layout(
         &self,
-        _tree: &Tree,
+        _tree: &mut Tree,
         _renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {

widget/src/qr_code.rs

@@ -60,7 +60,7 @@ impl<'a, Message, Theme> Widget<Message, Renderer<Theme>> for QRCode<'a> {
 
     fn layout(
         &self,
-        _tree: &Tree,
+        _tree: &mut Tree,
         _renderer: &Renderer<Theme>,
         _limits: &layout::Limits,
     ) -> layout::Node {

widget/src/radio.rs

@@ -211,7 +211,7 @@ where
 
     fn layout(
         &self,
-        tree: &Tree,
+        tree: &mut Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {
@@ -222,7 +222,7 @@ where
             |limits| {
                 let state = tree
                     .state
-                    .downcast_ref::<widget::text::State<Renderer::Paragraph>>();
+                    .downcast_mut::<widget::text::State<Renderer::Paragraph>>();
 
                 widget::text::layout(
                     state,

widget/src/row.rs

@@ -114,7 +114,7 @@ where
 
     fn layout(
         &self,
-        tree: &Tree,
+        tree: &mut Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {
@@ -128,7 +128,7 @@ where
             self.spacing,
             self.align_items,
             &self.children,
-            &tree.children,
+            &mut tree.children,
         )
     }
 

widget/src/rule.rs

@@ -72,7 +72,7 @@ where
 
     fn layout(
         &self,
-        _tree: &Tree,
+        _tree: &mut Tree,
         _renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {

widget/src/scrollable.rs

@@ -230,7 +230,7 @@ where
 
     fn layout(
         &self,
-        tree: &Tree,
+        tree: &mut Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {
@@ -242,7 +242,7 @@ where
             &self.direction,
             |renderer, limits| {
                 self.content.as_widget().layout(
-                    &tree.children[0],
+                    &mut tree.children[0],
                     renderer,
                     limits,
                 )

widget/src/slider.rs

@@ -169,7 +169,7 @@ where
 
     fn layout(
         &self,
-        _tree: &Tree,
+        _tree: &mut Tree,
         _renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {

widget/src/space.rs

@@ -55,7 +55,7 @@ where
 
     fn layout(
         &self,
-        _tree: &Tree,
+        _tree: &mut Tree,
         _renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {

widget/src/svg.rs

@@ -106,7 +106,7 @@ where
 
     fn layout(
         &self,
-        _tree: &Tree,
+        _tree: &mut Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {

widget/src/text_input.rs

@@ -30,8 +30,6 @@ use crate::core::{
 };
 use crate::runtime::Command;
 
-use std::cell::RefCell;
-
 pub use iced_style::text_input::{Appearance, StyleSheet};
 
 /// A field that can be filled with text.
@@ -267,7 +265,7 @@ where
 
     fn layout(
         &self,
-        tree: &Tree,
+        tree: &mut Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {
@@ -280,7 +278,7 @@ where
             self.font,
             self.line_height,
             self.icon.as_ref(),
-            tree.state.downcast_ref::<State<Renderer::Paragraph>>(),
+            tree.state.downcast_mut::<State<Renderer::Paragraph>>(),
             &self.value,
             &self.placeholder,
             self.is_secure,
@@ -469,7 +467,7 @@ pub fn layout<Renderer>(
     font: Option<Renderer::Font>,
     line_height: text::LineHeight,
     icon: Option<&Icon<Renderer::Font>>,
-    state: &State<Renderer::Paragraph>,
+    state: &mut State<Renderer::Paragraph>,
     value: &Value,
     placeholder: &str,
     is_secure: bool,
@@ -499,14 +497,12 @@ where
         shaping: text::Shaping::Advanced,
     };
 
-    renderer.update_paragraph(
+    renderer
-        &mut state.placeholder_paragraph.borrow_mut(),
+        .update_paragraph(&mut state.placeholder_paragraph, placeholder_text);
-        placeholder_text,
-    );
 
     if is_secure {
         renderer.update_paragraph(
-            &mut state.paragraph.borrow_mut(),
+            &mut state.paragraph,
             Text {
                 content: &value.secure().to_string(),
                 ..placeholder_text
@@ -514,7 +510,7 @@ where
         );
     } else {
         renderer.update_paragraph(
-            &mut state.paragraph.borrow_mut(),
+            &mut state.paragraph,
             Text {
                 content: &value.to_string(),
                 ..placeholder_text
@@ -1072,7 +1068,6 @@ pub fn draw<Renderer>(
     }
 
     let text = value.to_string();
-    let paragraph = &state.paragraph.borrow() as &Renderer::Paragraph;
 
     let (cursor, offset) = if let Some(focus) = state
         .is_focused
@@ -1083,7 +1078,7 @@ pub fn draw<Renderer>(
             cursor::State::Index(position) => {
                 let (text_value_width, offset) =
                     measure_cursor_and_scroll_offset(
-                        paragraph,
+                        &state.paragraph,
                         text_bounds,
                         position,
                     );
@@ -1121,14 +1116,14 @@ pub fn draw<Renderer>(
 
                 let (left_position, left_offset) =
                     measure_cursor_and_scroll_offset(
-                        paragraph,
+                        &state.paragraph,
                         text_bounds,
                         left,
                     );
 
                 let (right_position, right_offset) =
                     measure_cursor_and_scroll_offset(
-                        paragraph,
+                        &state.paragraph,
                         text_bounds,
                         right,
                     );
@@ -1162,7 +1157,7 @@ pub fn draw<Renderer>(
         (None, 0.0)
     };
 
-    let text_width = paragraph.min_width();
+    let text_width = state.paragraph.min_width();
 
     let render = |renderer: &mut Renderer| {
         if let Some((cursor, color)) = cursor {
@@ -1171,13 +1166,11 @@ pub fn draw<Renderer>(
             renderer.with_translation(Vector::ZERO, |_| {});
         }
 
-        let placeholder_paragraph = state.placeholder_paragraph.borrow();
-
         renderer.fill_paragraph(
             if text.is_empty() {
-                &placeholder_paragraph
+                &state.placeholder_paragraph
             } else {
-                paragraph
+                &state.paragraph
             },
             Point::new(text_bounds.x, text_bounds.center_y()),
             if text.is_empty() {
@@ -1219,8 +1212,8 @@ pub fn mouse_interaction(
 /// The state of a [`TextInput`].
 #[derive(Debug, Default, Clone)]
 pub struct State<P: text::Paragraph> {
-    paragraph: RefCell<P>,
+    paragraph: P,
-    placeholder_paragraph: RefCell<P>,
+    placeholder_paragraph: P,
     is_focused: Option<Focus>,
     is_dragging: bool,
     is_pasting: Option<Value>,
@@ -1246,8 +1239,8 @@ impl<P: text::Paragraph> State<P> {
     /// Creates a new [`State`], representing a focused [`TextInput`].
     pub fn focused() -> Self {
         Self {
-            paragraph: RefCell::new(P::default()),
+            paragraph: P::default(),
-            placeholder_paragraph: RefCell::new(P::default()),
+            placeholder_paragraph: P::default(),
             is_focused: None,
             is_dragging: false,
             is_pasting: None,
@@ -1364,7 +1357,7 @@ fn offset<P: text::Paragraph>(
         };
 
         let (_, offset) = measure_cursor_and_scroll_offset(
-            &state.paragraph.borrow() as &P,
+            &state.paragraph,
             text_bounds,
             focus_position,
         );
@@ -1402,7 +1395,6 @@ fn find_cursor_position<P: text::Paragraph>(
 
     let char_offset = state
         .paragraph
-        .borrow()
         .hit_test(Point::new(x + offset, text_bounds.height / 2.0))
         .map(text::Hit::cursor)?;
 
@@ -1432,7 +1424,7 @@ fn replace_paragraph<Renderer>(
     let mut children_layout = layout.children();
     let text_bounds = children_layout.next().unwrap().bounds();
 
-    *state.paragraph.get_mut() = renderer.create_paragraph(Text {
+    state.paragraph = renderer.create_paragraph(Text {
         font,
         line_height,
         content: &value.to_string(),

widget/src/toggler.rs

@@ -178,7 +178,7 @@ where
 
     fn layout(
         &self,
-        tree: &Tree,
+        tree: &mut Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {
@@ -192,7 +192,7 @@ where
                 if let Some(label) = self.label.as_deref() {
                     let state = tree
                     .state
-                    .downcast_ref::<widget::text::State<Renderer::Paragraph>>();
+                    .downcast_mut::<widget::text::State<Renderer::Paragraph>>();
 
                     widget::text::layout(
                         state,

widget/src/tooltip.rs

@@ -135,7 +135,7 @@ where
 
     fn layout(
         &self,
-        tree: &widget::Tree,
+        tree: &mut widget::Tree,
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {
@@ -302,7 +302,7 @@ where
     Renderer::Theme: container::StyleSheet + widget::text::StyleSheet,
 {
     tooltip: &'b Text<'a, Renderer>,
-    state: &'b widget::Tree,
+    state: &'b mut widget::Tree,
     cursor_position: Point,
     content_bounds: Rectangle,
     snap_within_viewport: bool,
@@ -319,7 +319,7 @@ where
     Renderer::Theme: container::StyleSheet + widget::text::StyleSheet,
 {
     fn layout(
-        &self,
+        &mut self,
         renderer: &Renderer,
         bounds: Size,
         position: Point,

widget/src/vertical_slider.rs

@@ -166,7 +166,7 @@ where
 
     fn layout(
         &self,
-        _tree: &Tree,
+        _tree: &mut Tree,
         _renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {