Implement explicit text caching in the widget state tree

core/src/text.rs

@@ -1,6 +1,6 @@
 //! Draw and interact with text.
 use crate::alignment;
-use crate::{Color, Pixels, Point, Rectangle, Size};
+use crate::{Color, Pixels, Point, Size};
 
 use std::borrow::Cow;
 use std::hash::{Hash, Hasher};
@@ -12,17 +12,14 @@ pub struct Text<'a, Font> {
     pub content: &'a str,
 
     /// The bounds of the paragraph.
-    pub bounds: Rectangle,
+    pub bounds: Size,
 
     /// The size of the [`Text`] in logical pixels.
-    pub size: f32,
+    pub size: Pixels,
 
     /// The line height of the [`Text`].
     pub line_height: LineHeight,
 
-    /// The color of the [`Text`].
-    pub color: Color,
-
     /// The font of the [`Text`].
     pub font: Font,
 
@@ -132,7 +129,10 @@ impl Hit {
 /// A renderer capable of measuring and drawing [`Text`].
 pub trait Renderer: crate::Renderer {
     /// The font type used.
-    type Font: Copy;
+    type Font: Copy + PartialEq;
+
+    /// The [`Paragraph`] of this [`Renderer`].
+    type Paragraph: Paragraph<Font = Self::Font> + 'static;
 
     /// The icon font of the backend.
     const ICON_FONT: Self::Font;
@@ -151,62 +151,107 @@ pub trait Renderer: crate::Renderer {
     fn default_font(&self) -> Self::Font;
 
     /// Returns the default size of [`Text`].
-    fn default_size(&self) -> f32;
-
-    /// Measures the text in the given bounds and returns the minimum boundaries
-    /// that can fit the contents.
-    fn measure(
-        &self,
-        content: &str,
-        size: f32,
-        line_height: LineHeight,
-        font: Self::Font,
-        bounds: Size,
-        shaping: Shaping,
-    ) -> Size;
-
-    /// Measures the width of the text as if it were laid out in a single line.
-    fn measure_width(
-        &self,
-        content: &str,
-        size: f32,
-        font: Self::Font,
-        shaping: Shaping,
-    ) -> f32 {
-        let bounds = self.measure(
-            content,
-            size,
-            LineHeight::Absolute(Pixels(size)),
-            font,
-            Size::INFINITY,
-            shaping,
-        );
-
-        bounds.width
-    }
-
-    /// Tests whether the provided point is within the boundaries of text
-    /// laid out with the given parameters, returning information about
-    /// the nearest character.
-    ///
-    /// If `nearest_only` is true, the hit test does not consider whether the
-    /// the point is interior to any glyph bounds, returning only the character
-    /// with the nearest centeroid.
-    fn hit_test(
-        &self,
-        contents: &str,
-        size: f32,
-        line_height: LineHeight,
-        font: Self::Font,
-        bounds: Size,
-        shaping: Shaping,
-        point: Point,
-        nearest_only: bool,
-    ) -> Option<Hit>;
+    fn default_size(&self) -> Pixels;
 
     /// Loads a [`Self::Font`] from its bytes.
     fn load_font(&mut self, font: Cow<'static, [u8]>);
 
-    /// Draws the given [`Text`].
-    fn fill_text(&mut self, text: Text<'_, Self::Font>);
+    /// Creates a new [`Paragraph`] laid out with the given [`Text`].
+    fn create_paragraph(&self, text: Text<'_, Self::Font>) -> Self::Paragraph;
+
+    /// Lays out the given [`Paragraph`] with some new boundaries.
+    fn resize_paragraph(
+        &self,
+        paragraph: &mut Self::Paragraph,
+        new_bounds: Size,
+    );
+
+    /// Updates a [`Paragraph`] to match the given [`Text`], if needed.
+    fn update_paragraph(
+        &self,
+        paragraph: &mut Self::Paragraph,
+        text: Text<'_, Self::Font>,
+    ) {
+        if paragraph.content() != text.content
+            || paragraph.text_size() != text.size
+            || paragraph.line_height().to_absolute(text.size)
+                != text.line_height.to_absolute(text.size)
+            || paragraph.font() != text.font
+            || paragraph.shaping() != text.shaping
+            || paragraph.horizontal_alignment() != text.horizontal_alignment
+            || paragraph.vertical_alignment() != text.vertical_alignment
+        {
+            *paragraph = self.create_paragraph(text);
+        } else if paragraph.bounds() != text.bounds {
+            self.resize_paragraph(paragraph, text.bounds);
+        }
+    }
+
+    /// Draws the given [`Paragraph`] at the given position and with the given
+    /// [`Color`].
+    fn fill_paragraph(
+        &mut self,
+        text: &Self::Paragraph,
+        position: Point,
+        color: Color,
+    );
+
+    /// Draws the given [`Text`] at the given position and with the given
+    /// [`Color`].
+    fn fill_text(
+        &mut self,
+        text: Text<'_, Self::Font>,
+        position: Point,
+        color: Color,
+    );
+}
+/// A text paragraph.
+pub trait Paragraph: Default {
+    /// The font of this [`Paragraph`].
+    type Font;
+
+    /// Returns the content of the [`Paragraph`].
+    fn content(&self) -> &str;
+
+    /// Returns the text size of the [`Paragraph`].
+    fn text_size(&self) -> Pixels;
+
+    /// Returns the [`LineHeight`] of the [`Paragraph`].
+    fn line_height(&self) -> LineHeight;
+
+    /// Returns the [`Font`] of the [`Paragraph`].
+    fn font(&self) -> Self::Font;
+
+    /// Returns the [`Shaping`] strategy of the [`Paragraph`].
+    fn shaping(&self) -> Shaping;
+
+    /// Returns the horizontal alignment of the [`Paragraph`].
+    fn horizontal_alignment(&self) -> alignment::Horizontal;
+
+    /// Returns the vertical alignment of the [`Paragraph`].
+    fn vertical_alignment(&self) -> alignment::Vertical;
+
+    /// Returns the boundaries of the [`Paragraph`].
+    fn bounds(&self) -> Size;
+
+    /// Returns the minimum boundaries that can fit the contents of the
+    /// [`Paragraph`].
+    fn min_bounds(&self) -> Size;
+
+    /// Tests whether the provided point is within the boundaries of the
+    /// [`Paragraph`], returning information about the nearest character.
+    fn hit_test(&self, point: Point) -> Option<Hit>;
+
+    /// Returns the distance to the given grapheme index in the [`Paragraph`].
+    fn grapheme_position(&self, line: usize, index: usize) -> Option<Point>;
+
+    /// Returns the minimum width that can fit the contents of the [`Paragraph`].
+    fn min_width(&self) -> f32 {
+        self.min_bounds().width
+    }
+
+    /// Returns the minimum height that can fit the contents of the [`Paragraph`].
+    fn min_height(&self) -> f32 {
+        self.min_bounds().height
+    }
 }