Decouple caching from Paragraph API

core/src/renderer/null.rs

@@ -79,7 +79,7 @@ impl text::Paragraph for () {
 
     fn resize(&mut self, _new_bounds: Size) {}
 
-    fn compare(&self, _text: Text<&str>) -> text::Difference {
+    fn compare(&self, _text: Text<()>) -> text::Difference {
         text::Difference::None
     }
 

core/src/text.rs

@@ -1,8 +1,7 @@
 //! Draw and interact with text.
-mod paragraph;
-
 pub mod editor;
 pub mod highlighter;
+pub mod paragraph;
 
 pub use editor::Editor;
 pub use highlighter::Highlighter;

core/src/text/paragraph.rs

@@ -1,3 +1,4 @@
+//! Draw paragraphs.
 use crate::alignment;
 use crate::text::{Difference, Hit, Text};
 use crate::{Point, Size};
@@ -15,7 +16,7 @@ pub trait Paragraph: Sized + Default {
 
     /// Compares the [`Paragraph`] with some desired [`Text`] and returns the
     /// [`Difference`].
-    fn compare(&self, text: Text<&str, Self::Font>) -> Difference;
+    fn compare(&self, text: Text<(), Self::Font>) -> Difference;
 
     /// Returns the horizontal alignment of the [`Paragraph`].
     fn horizontal_alignment(&self) -> alignment::Horizontal;
@@ -34,19 +35,6 @@ pub trait Paragraph: Sized + Default {
     /// Returns the distance to the given grapheme index in the [`Paragraph`].
     fn grapheme_position(&self, line: usize, index: usize) -> Option<Point>;
 
-    /// Updates the [`Paragraph`] to match the given [`Text`], if needed.
-    fn update(&mut self, text: Text<&str, Self::Font>) {
-        match self.compare(text) {
-            Difference::None => {}
-            Difference::Bounds => {
-                self.resize(text.bounds);
-            }
-            Difference::Shape => {
-                *self = Self::with_text(text);
-            }
-        }
-    }
-
     /// Returns the minimum width that can fit the contents of the [`Paragraph`].
     fn min_width(&self) -> f32 {
         self.min_bounds().width
@@ -57,3 +45,77 @@ pub trait Paragraph: Sized + Default {
         self.min_bounds().height
     }
 }
+
+/// A [`Paragraph`] of plain text.
+#[derive(Debug, Clone, Default)]
+pub struct Plain<P: Paragraph> {
+    raw: P,
+    content: String,
+}
+
+impl<P: Paragraph> Plain<P> {
+    /// Creates a new [`Plain`] paragraph.
+    pub fn new(text: Text<&str, P::Font>) -> Self {
+        let content = text.content.to_owned();
+
+        Self {
+            raw: P::with_text(text),
+            content,
+        }
+    }
+
+    /// Updates the plain [`Paragraph`] to match the given [`Text`], if needed.
+    pub fn update(&mut self, text: Text<&str, P::Font>) {
+        if self.content != text.content {
+            text.content.clone_into(&mut self.content);
+            self.raw = P::with_text(text);
+            return;
+        }
+
+        match self.raw.compare(Text {
+            content: (),
+            bounds: text.bounds,
+            size: text.size,
+            line_height: text.line_height,
+            font: text.font,
+            horizontal_alignment: text.horizontal_alignment,
+            vertical_alignment: text.vertical_alignment,
+            shaping: text.shaping,
+        }) {
+            Difference::None => {}
+            Difference::Bounds => {
+                self.raw.resize(text.bounds);
+            }
+            Difference::Shape => {
+                self.raw = P::with_text(text);
+            }
+        }
+    }
+
+    /// Returns the horizontal alignment of the [`Paragraph`].
+    pub fn horizontal_alignment(&self) -> alignment::Horizontal {
+        self.raw.horizontal_alignment()
+    }
+
+    /// Returns the vertical alignment of the [`Paragraph`].
+    pub fn vertical_alignment(&self) -> alignment::Vertical {
+        self.raw.vertical_alignment()
+    }
+
+    /// Returns the minimum boundaries that can fit the contents of the
+    /// [`Paragraph`].
+    pub fn min_bounds(&self) -> Size {
+        self.raw.min_bounds()
+    }
+
+    /// Returns the minimum width that can fit the contents of the
+    /// [`Paragraph`].
+    pub fn min_width(&self) -> f32 {
+        self.raw.min_width()
+    }
+
+    /// Returns the cached [`Paragraph`].
+    pub fn raw(&self) -> &P {
+        &self.raw
+    }
+}

core/src/widget/text.rs

@@ -3,7 +3,8 @@ use crate::alignment;
 use crate::layout;
 use crate::mouse;
 use crate::renderer;
-use crate::text::{self, Paragraph};
+use crate::text;
+use crate::text::paragraph::{self, Paragraph};
 use crate::widget::tree::{self, Tree};
 use crate::{
     Color, Element, Layout, Length, Pixels, Point, Rectangle, Size, Theme,
@@ -155,7 +156,7 @@ where
 
 /// The internal state of a [`Text`] widget.
 #[derive(Debug, Default)]
-pub struct State<P: Paragraph>(P);
+pub struct State<P: Paragraph>(paragraph::Plain<P>);
 
 impl<'a, Message, Theme, Renderer> Widget<Message, Theme, Renderer>
     for Text<'a, Theme, Renderer>
@@ -168,7 +169,9 @@ where
     }
 
     fn state(&self) -> tree::State {
-        tree::State::new(State(Renderer::Paragraph::default()))
+        tree::State::new(State::<Renderer::Paragraph>(
+            paragraph::Plain::default(),
+        ))
     }
 
     fn size(&self) -> Size<Length> {
@@ -294,7 +297,7 @@ pub fn draw<Renderer>(
     };
 
     renderer.fill_paragraph(
-        paragraph,
+        paragraph.raw(),
         Point::new(x, y),
         appearance.color.unwrap_or(style.text_color),
         *viewport,