Compute width of shaped text on-demand (#6806)

crates/typst-layout/src/inline/collect.rs

@@ -82,7 +82,7 @@ impl<'a> Item<'a> {
     /// The natural layouted width of the item.
     pub fn natural_width(&self) -> Abs {
         match self {
-            Self::Text(shaped) => shaped.width,
+            Self::Text(shaped) => shaped.width(),
             Self::Absolute(v, _) => *v,
             Self::Frame(frame) => frame.width(),
             Self::Fractional(_, _) | Self::Tag(_) => Abs::zero(),

crates/typst-layout/src/inline/line.rs

@@ -364,7 +364,6 @@ fn adjust_cj_at_line_start(p: &Preparation, items: &mut Items) {
         let glyph = shaped.glyphs.to_mut().first_mut().unwrap();
         let shrink = glyph.shrinkability().0;
         glyph.shrink_left(shrink);
-        shaped.width -= shrink.at(glyph.size);
     } else if p.config.cjk_latin_spacing
         && glyph.is_cj_script()
         && glyph.x_offset > Em::zero()
@@ -376,7 +375,6 @@ fn adjust_cj_at_line_start(p: &Preparation, items: &mut Items) {
         glyph.x_advance -= shrink;
         glyph.x_offset = Em::zero();
         glyph.adjustability.shrinkability.0 = Em::zero();
-        shaped.width -= shrink.at(glyph.size);
     }
 }
 
@@ -394,7 +392,6 @@ fn adjust_cj_at_line_end(p: &Preparation, items: &mut Items) {
         let shrink = glyph.shrinkability().1;
         let punct = shaped.glyphs.to_mut().last_mut().unwrap();
         punct.shrink_right(shrink);
-        shaped.width -= shrink.at(punct.size);
     } else if p.config.cjk_latin_spacing
         && glyph.is_cj_script()
         && (glyph.x_advance - glyph.x_offset) > Em::one()
@@ -405,7 +402,6 @@ fn adjust_cj_at_line_end(p: &Preparation, items: &mut Items) {
         let glyph = shaped.glyphs.to_mut().last_mut().unwrap();
         glyph.x_advance -= shrink;
         glyph.adjustability.shrinkability.1 = Em::zero();
-        shaped.width -= shrink.at(glyph.size);
     }
 }
 

crates/typst-layout/src/inline/prepare.rs

@@ -152,7 +152,6 @@ fn add_cjk_latin_spacing(items: &mut [(Range, Item)]) {
                 // The spacing is default to 1/4 em, and can be shrunk to 1/8 em.
                 glyph.x_advance += Em::new(0.25);
                 glyph.adjustability.shrinkability.1 += Em::new(0.125);
-                text.width += Em::new(0.25).at(glyph.size);
             }
 
             // Case 2: Latin followed by a CJ character
@@ -160,7 +159,6 @@ fn add_cjk_latin_spacing(items: &mut [(Range, Item)]) {
                 glyph.x_advance += Em::new(0.25);
                 glyph.x_offset += Em::new(0.25);
                 glyph.adjustability.shrinkability.0 += Em::new(0.125);
-                text.width += Em::new(0.25).at(glyph.size);
             }
 
             prev = Some(glyph);

crates/typst-layout/src/inline/shaping.rs

@@ -47,8 +47,6 @@ pub struct ShapedText<'a> {
     pub styles: StyleChain<'a>,
     /// The font variant.
     pub variant: FontVariant,
-    /// The width of the text's bounding box.
-    pub width: Abs,
     /// The shaped glyphs.
     pub glyphs: Cow<'a, [ShapedGlyph]>,
 }
@@ -214,7 +212,7 @@ impl<'a> ShapedText<'a> {
         extra_justification: Abs,
     ) -> Frame {
         let (top, bottom) = self.measure(engine);
-        let size = Size::new(self.width, top + bottom);
+        let size = Size::new(self.width(), top + bottom);
 
         let mut offset = Abs::zero();
         let mut frame = Frame::soft(size);
@@ -332,6 +330,12 @@ impl<'a> ShapedText<'a> {
         frame
     }
 
+    /// Computes the width of a run of glyphs relative to the font size,
+    /// accounting for their individual scaling factors and other font metrics.
+    pub fn width(&self) -> Abs {
+        self.glyphs.iter().map(|g| g.x_advance.at(g.size)).sum()
+    }
+
     /// Measure the top and bottom extent of this text.
     pub fn measure(&self, engine: &Engine) -> (Abs, Abs) {
         let mut top = Abs::zero();
@@ -419,7 +423,6 @@ impl<'a> ShapedText<'a> {
                 region: self.region,
                 styles: self.styles,
                 variant: self.variant,
-                width: glyphs_width(glyphs),
                 glyphs: Cow::Borrowed(glyphs),
             }
         } else {
@@ -437,12 +440,7 @@ impl<'a> ShapedText<'a> {
 
     /// Derive an empty text run with the same properties as this one.
     pub fn empty(&self) -> Self {
-        Self {
+        Self { text: "", glyphs: Cow::Borrowed(&[]), ..*self }
-            text: "",
-            width: Abs::zero(),
-            glyphs: Cow::Borrowed(&[]),
-            ..*self
-        }
     }
 
     /// Creates shaped text containing a hyphen.
@@ -485,7 +483,6 @@ impl<'a> ShapedText<'a> {
                 region: base.region,
                 styles: base.styles,
                 variant: base.variant,
-                width: x_advance.at(size),
                 glyphs: Cow::Owned(vec![ShapedGlyph {
                     font,
                     glyph_id: glyph_id.0,
@@ -694,17 +691,10 @@ fn shape<'a>(
         region,
         styles,
         variant: ctx.variant,
-        width: glyphs_width(&ctx.glyphs),
         glyphs: Cow::Owned(ctx.glyphs),
     }
 }
 
-/// Computes the width of a run of glyphs relative to the font size, accounting
-/// for their individual scaling factors and other font metrics.
-fn glyphs_width(glyphs: &[ShapedGlyph]) -> Abs {
-    glyphs.iter().map(|g| g.x_advance.at(g.size)).sum()
-}
-
 /// Holds shaping results and metadata common to all shaped segments.
 struct ShapingContext<'a, 'v> {
     engine: &'a Engine<'v>,