Support configurable LineHeight in text widgets

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,