Support configurable `LineHeight` in text widgets

5 files changed, 104 insertions, 5 deletions

diff --git a/core/src/length.rs b/core/src/length.rs
index bb925c4b..3adb996e 100644
--- a/core/src/length.rs
+++ b/core/src/length.rs
@@ -1,3 +1,5 @@
+use crate::Pixels;
+
 /// The strategy used to fill space in a specific dimension.
 #[derive(Debug, Clone, Copy, PartialEq)]
 pub enum Length {
@@ -36,6 +38,12 @@ impl Length {
     }
 }
 
+impl From<Pixels> for Length {
+    fn from(amount: Pixels) -> Self {
+        Length::Fixed(f32::from(amount))
+    }
+}
+
 impl From<f32> for Length {
     fn from(amount: f32) -> Self {
         Length::Fixed(amount)
diff --git a/core/src/pixels.rs b/core/src/pixels.rs
index e42cd9f9..6a9e5c88 100644
--- a/core/src/pixels.rs
+++ b/core/src/pixels.rs
@@ -20,3 +20,9 @@ impl From<u16> for Pixels {
         Self(f32::from(amount))
     }
 }
+
+impl From<Pixels> for f32 {
+    fn from(pixels: Pixels) -> Self {
+        pixels.0
+    }
+}
diff --git a/core/src/renderer/null.rs b/core/src/renderer/null.rs
index 22afb058..f0cc952e 100644
--- a/core/src/renderer/null.rs
+++ b/core/src/renderer/null.rs
@@ -60,6 +60,7 @@ impl text::Renderer for Null {
         &self,
         _content: &str,
         _size: f32,
+        _line_height: text::LineHeight,
         _font: Font,
         _bounds: Size,
         _shaping: text::Shaping,
@@ -71,6 +72,7 @@ impl text::Renderer for Null {
         &self,
         _contents: &str,
         _size: f32,
+        _line_height: text::LineHeight,
         _font: Self::Font,
         _bounds: Size,
         _shaping: text::Shaping,
diff --git a/core/src/text.rs b/core/src/text.rs
index c59d8fce..1a867be3 100644
--- a/core/src/text.rs
+++ b/core/src/text.rs
@@ -1,8 +1,9 @@
 //! Draw and interact with text.
 use crate::alignment;
-use crate::{Color, Point, Rectangle, Size};
+use crate::{Color, Pixels, Point, Rectangle, Size};
 
 use std::borrow::Cow;
+use std::hash::{Hash, Hasher};
 
 /// A paragraph.
 #[derive(Debug, Clone, Copy)]
@@ -13,9 +14,12 @@ pub struct Text<'a, Font> {
     /// The bounds of the paragraph.
     pub bounds: Rectangle,
 
-    /// The size of the [`Text`].
+    /// The size of the [`Text`] in logical pixels.
     pub size: f32,
 
+    /// The line height of the [`Text`].
+    pub line_height: LineHeight,
+
     /// The color of the [`Text`].
     pub color: Color,
 
@@ -56,6 +60,59 @@ pub enum Shaping {
     Advanced,
 }
 
+/// The height of a line of text in a paragraph.
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum LineHeight {
+    /// A factor of the size of the text.
+    Relative(f32),
+
+    /// An absolute height in logical pixels.
+    Absolute(Pixels),
+}
+
+impl LineHeight {
+    /// Returns the [`LineHeight`] in absolute logical pixels.
+    pub fn to_absolute(self, text_size: Pixels) -> Pixels {
+        match self {
+            Self::Relative(factor) => Pixels(factor * text_size.0),
+            Self::Absolute(pixels) => pixels,
+        }
+    }
+}
+
+impl Default for LineHeight {
+    fn default() -> Self {
+        Self::Relative(1.2)
+    }
+}
+
+impl From<f32> for LineHeight {
+    fn from(factor: f32) -> Self {
+        Self::Relative(factor)
+    }
+}
+
+impl From<Pixels> for LineHeight {
+    fn from(pixels: Pixels) -> Self {
+        Self::Absolute(pixels)
+    }
+}
+
+impl Hash for LineHeight {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        match self {
+            Self::Relative(factor) => {
+                state.write_u8(0);
+                factor.to_bits().hash(state);
+            }
+            Self::Absolute(pixels) => {
+                state.write_u8(1);
+                f32::from(*pixels).to_bits().hash(state);
+            }
+        }
+    }
+}
+
 /// The result of hit testing on text.
 #[derive(Debug, Clone, Copy, PartialEq)]
 pub enum Hit {
@@ -102,6 +159,7 @@ pub trait Renderer: crate::Renderer {
         &self,
         content: &str,
         size: f32,
+        line_height: LineHeight,
         font: Self::Font,
         bounds: Size,
         shaping: Shaping,
@@ -115,8 +173,14 @@ pub trait Renderer: crate::Renderer {
         font: Self::Font,
         shaping: Shaping,
     ) -> f32 {
-        let (width, _) =
-            self.measure(content, size, font, Size::INFINITY, shaping);
+        let (width, _) = self.measure(
+            content,
+            size,
+            LineHeight::Absolute(Pixels(size)),
+            font,
+            Size::INFINITY,
+            shaping,
+        );
 
         width
     }
@@ -132,6 +196,7 @@ pub trait Renderer: crate::Renderer {
         &self,
         contents: &str,
         size: f32,
+        line_height: LineHeight,
         font: Self::Font,
         bounds: Size,
         shaping: Shaping,
diff --git a/core/src/widget/text.rs b/core/src/widget/text.rs
index f0392168..2d86e735 100644
--- a/core/src/widget/text.rs
+++ b/core/src/widget/text.rs
@@ -19,6 +19,7 @@ where
 {
     content: Cow<'a, str>,
     size: Option<f32>,
+    line_height: text::LineHeight,
     width: Length,
     height: Length,
     horizontal_alignment: alignment::Horizontal,
@@ -38,6 +39,7 @@ where
         Text {
             content: content.into(),
             size: None,
+            line_height: text::LineHeight::default(),
             font: None,
             width: Length::Shrink,
             height: Length::Shrink,
@@ -54,6 +56,15 @@ where
         self
     }
 
+    /// Sets the [`LineHeight`] of the [`Text`].
+    pub fn line_height(
+        mut self,
+        line_height: impl Into<text::LineHeight>,
+    ) -> Self {
+        self.line_height = line_height.into();
+        self
+    }
+
     /// Sets the [`Font`] of the [`Text`].
     ///
     /// [`Font`]: crate::text::Renderer::Font
@@ -135,6 +146,7 @@ where
         let (width, height) = renderer.measure(
             &self.content,
             size,
+            self.line_height,
             self.font.unwrap_or_else(|| renderer.default_font()),
             bounds,
             self.shaping,
@@ -161,6 +173,7 @@ where
             layout,
             &self.content,
             self.size,
+            self.line_height,
             self.font,
             theme.appearance(self.style.clone()),
             self.horizontal_alignment,
@@ -186,6 +199,7 @@ pub fn draw<Renderer>(
     layout: Layout<'_>,
     content: &str,
     size: Option<f32>,
+    line_height: text::LineHeight,
     font: Option<Renderer::Font>,
     appearance: Appearance,
     horizontal_alignment: alignment::Horizontal,
@@ -208,9 +222,12 @@ pub fn draw<Renderer>(
         alignment::Vertical::Bottom => bounds.y + bounds.height,
     };
 
+    let size = size.unwrap_or_else(|| renderer.default_size());
+
     renderer.fill_text(crate::Text {
         content,
-        size: size.unwrap_or_else(|| renderer.default_size()),
+        size,
+        line_height,
         bounds: Rectangle { x, y, ..bounds },
         color: appearance.color.unwrap_or(style.text_color),
         font: font.unwrap_or_else(|| renderer.default_font()),
@@ -240,6 +257,7 @@ where
         Self {
             content: self.content.clone(),
             size: self.size,
+            line_height: self.line_height,
             width: self.width,
             height: self.height,
             horizontal_alignment: self.horizontal_alignment,