Fix scales for unit conversion (#5169)

Author: laurmaedje

crates/typst-ide/src/jump.rs

@@ -205,7 +205,7 @@ mod tests {
 
     macro_rules! assert_approx_eq {
         ($l:expr, $r:expr) => {
-            assert!(($l.to_raw() - $r.to_raw()).abs() < 0.1, "{:?} ≉ {:?}", $l, $r);
+            assert!(($l - $r).abs() < Abs::pt(0.1), "{:?} ≉ {:?}", $l, $r);
         };
     }
 

crates/typst-render/src/text.rs

@@ -13,27 +13,26 @@ use crate::{shape, AbsExt, State};
 
 /// Render a text run into the canvas.
 pub fn render_text(canvas: &mut sk::Pixmap, state: State, text: &TextItem) {
-    let mut x = 0.0;
+    let mut x = Abs::zero();
     for glyph in &text.glyphs {
         let id = GlyphId(glyph.id);
-        let offset = x + glyph.x_offset.at(text.size).to_f32();
+        let offset = x + glyph.x_offset.at(text.size);
 
         if should_outline(&text.font, glyph) {
-            let state =
-                state.pre_translate(Point::new(Abs::raw(offset as _), Abs::raw(0.0)));
+            let state = state.pre_translate(Point::with_x(offset));
             render_outline_glyph(canvas, state, text, id);
         } else {
             let upem = text.font.units_per_em();
-            let text_scale = Abs::raw(text.size.to_raw() / upem);
+            let text_scale = text.size / upem;
             let state = state
-                .pre_translate(Point::new(Abs::raw(offset as _), -text.size))
+                .pre_translate(Point::new(offset, -text.size))
                 .pre_scale(Axes::new(text_scale, text_scale));
 
             let (glyph_frame, _) = glyph_frame(&text.font, glyph.id);
             crate::render_frame(canvas, state, &glyph_frame);
         }
 
-        x += glyph.x_advance.at(text.size).to_f32();
+        x += glyph.x_advance.at(text.size);
     }
 }
 

crates/typst-svg/src/text.rs

@@ -55,15 +55,15 @@ impl SVGRenderer {
         scale: f64,
     ) -> Option<()> {
         let data_url = convert_svg_glyph_to_base64_url(&text.font, id)?;
-        let upem = Abs::raw(text.font.units_per_em());
-        let origin_ascender = text.font.metrics().ascender.at(upem).to_pt();
+        let upem = text.font.units_per_em();
+        let origin_ascender = text.font.metrics().ascender.at(Abs::pt(upem));
 
         let glyph_hash = hash128(&(&text.font, id));
         let id = self.glyphs.insert_with(glyph_hash, || RenderedGlyph::Image {
             url: data_url,
-            width: upem.to_pt(),
-            height: upem.to_pt(),
-            ts: Transform::translate(Abs::zero(), Abs::pt(-origin_ascender))
+            width: upem,
+            height: upem,
+            ts: Transform::translate(Abs::zero(), -origin_ascender)
                 .post_concat(Transform::scale(Ratio::new(scale), Ratio::new(-scale))),
         });
 
@@ -260,9 +260,10 @@ fn convert_svg_glyph_to_base64_url(font: &Font, id: GlyphId) -> Option<EcoString
         data = &decoded;
     }
 
-    let upem = Abs::raw(font.units_per_em());
-    let (width, height) = (upem.to_pt(), upem.to_pt());
-    let origin_ascender = font.metrics().ascender.at(upem).to_pt();
+    let upem = font.units_per_em();
+    let width = upem;
+    let height = upem;
+    let origin_ascender = font.metrics().ascender.at(Abs::pt(upem));
 
     // Parse XML.
     let mut svg_str = std::str::from_utf8(data).ok()?.to_owned();
@@ -296,7 +297,8 @@ fn convert_svg_glyph_to_base64_url(font: &Font, id: GlyphId) -> Option<EcoString
         // make sure the glyph is rendered at the correct position
         svg_str.insert_str(
             start_span.unwrap().range().end,
-            format!(r#" viewBox="0 {} {width} {height}""#, -origin_ascender).as_str(),
+            format!(r#" viewBox="0 {} {width} {height}""#, -origin_ascender.to_pt())
+                .as_str(),
         );
     }
 

crates/typst/src/layout/abs.rs

@@ -7,9 +7,6 @@ use ecow::EcoString;
 use crate::foundations::{cast, repr, Fold, Repr, Value};
 use crate::utils::{Numeric, Scalar};
 
-/// The epsilon for approximate comparisons.
-const EPS: f64 = 1e-6;
-
 /// An absolute length.
 #[derive(Default, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
 pub struct Abs(Scalar);
@@ -113,17 +110,17 @@ impl Abs {
     /// Whether the other absolute length fits into this one (i.e. is smaller).
     /// Allows for a bit of slack.
     pub fn fits(self, other: Self) -> bool {
-        self.0 + EPS >= other.0
+        self.0 + AbsUnit::EPS >= other.0
     }
 
     /// Compares two absolute lengths for whether they are approximately equal.
     pub fn approx_eq(self, other: Self) -> bool {
-        self == other || (self - other).to_raw().abs() < EPS
+        self == other || (self - other).to_raw().abs() < AbsUnit::EPS
     }
 
     /// Whether the size is close to zero or negative.
     pub fn approx_empty(self) -> bool {
-        self.to_raw() <= EPS
+        self.to_raw() <= AbsUnit::EPS
     }
 
     /// Returns a number that represent the sign of this length
@@ -254,13 +251,19 @@ pub enum AbsUnit {
 }
 
 impl AbsUnit {
+    /// The epsilon for approximate length comparisons.
+    const EPS: f64 = 1e-4;
+
     /// How many raw units correspond to a value of `1.0` in this unit.
-    fn raw_scale(self) -> f64 {
+    const fn raw_scale(self) -> f64 {
+        // We choose a raw scale which has an integer conversion value to all
+        // four units of interest, so that whole numbers in all units can be
+        // represented accurately.
         match self {
-            AbsUnit::Pt => 1.0,
-            AbsUnit::Mm => 2.83465,
-            AbsUnit::Cm => 28.3465,
-            AbsUnit::In => 72.0,
+            AbsUnit::Pt => 127.0,
+            AbsUnit::Mm => 360.0,
+            AbsUnit::Cm => 3600.0,
+            AbsUnit::In => 9144.0,
         }
     }
 }

crates/typst/src/text/font/color.rs

@@ -186,9 +186,8 @@ fn draw_colr_glyph(
     )
     .ok()?;
 
-    let y_shift = Abs::raw(upem.to_raw() - y_max);
-
-    let position = Point::new(Abs::raw(x_min), y_shift);
+    let y_shift = Abs::pt(upem.to_pt() - y_max);
+    let position = Point::new(Abs::pt(x_min), y_shift);
     let size = Size::new(Abs::pt(width), Abs::pt(height));
     frame.push(position, FrameItem::Image(image, size, Span::detached()));
 

tests/ref/gradient-presets.png

@@ -9,24 +9,26 @@
 
 --- length-to-unit ---
 // Test length unit conversions.
-#test((500.934pt).pt(), 500.934)
-#test((3.3453cm).cm(), 3.3453)
-#test((4.3452mm).mm(), 4.3452)
-#test((5.345in).inches(), 5.345)
-#test((500.333666999pt).pt(), 500.333666999)
-#test((3.5234354cm).cm(), 3.5234354)
-#test((4.12345678mm).mm(), 4.12345678)
-#test((5.333666999in).inches(), 5.333666999)
-#test((4.123456789123456mm).mm(), 4.123456789123456)
-#test((254cm).mm(), 2540.0)
-#test(calc.round((254cm).inches(), digits: 2), 100.0)
-#test((2540mm).cm(), 254.0)
-#test(calc.round((2540mm).inches(), digits: 2), 100.0)
-#test((100in).pt(), 7200.0)
-#test(calc.round((100in).cm(), digits: 2), 254.0)
-#test(calc.round((100in).mm(), digits: 2), 2540.0)
-#test(5em.abs.cm(), 0.0)
-#test((5em + 6in).abs.inches(), 6.0)
+#let t(a, b) = assert(calc.abs(a - b) < 1e-6)
+
+#t((500.934pt).pt(), 500.934)
+#t((3.3453cm).cm(), 3.3453)
+#t((4.3452mm).mm(), 4.3452)
+#t((5.345in).inches(), 5.345)
+#t((500.333666999pt).pt(), 500.333666999)
+#t((3.523435cm).cm(), 3.523435)
+#t((4.12345678mm).mm(), 4.12345678)
+#t((5.333666999in).inches(), 5.333666999)
+#t((4.123456789123456mm).mm(), 4.123456789123456)
+#t((254cm).mm(), 2540.0)
+#t((254cm).inches(), 100.0)
+#t((2540mm).cm(), 254.0)
+#t((2540mm).inches(), 100.0)
+#t((100in).pt(), 7200.0)
+#t((100in).cm(), 254.0)
+#t((100in).mm(), 2540.0)
+#t(5em.abs.cm(), 0.0)
+#t((5em + 6in).abs.inches(), 6.0)
 
 --- length-to-absolute ---
 // Test length `to-absolute` method.