Decouple caching from Paragraph API

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
+    }
+}