Typography: a formula picture is as wide as its formula (px, not pt)

src/navigation/tests/tabs.rs

@@ -191,7 +191,11 @@ struct Sheets {
 impl Render for Sheets {
     fn render(&mut self, _: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
         let view = cx.entity();
-        let tail = if self.long { "W".repeat(40) } else { String::new() };
+        let tail = if self.long {
+            "W".repeat(40)
+        } else {
+            String::new()
+        };
         let tabs = (0..30).map(|ix| Choice::new(format!("s{ix}"), format!("Sheet {ix}{tail}")));
         div()
             .w(px(self.width))

src/typography/math.rs

@@ -166,7 +166,9 @@ fn laid(formula: &Formula) -> Result<(String, f32, f32), MathError> {
         (list.width * font, (list.height + list.depth) * font, svg)
     })?;
     let (width, height, svg) = typeset;
-    Ok((svg, width as f32, height as f32))
+    let (width, height) = (width as f32, height as f32);
+    // RaTeX sizes its svg in pt; px keeps one unit.
+    Ok((wrapped(&svg, [0.0, 0.0, width, height])?, width, height))
 }
 
 /// Runs RaTeX's layout; a panic becomes an error.
@@ -187,18 +189,22 @@ fn framed(svg: &str, width: f32, height: f32) -> Result<(String, Size<Pixels>),
     let top = ink.top().min(0.0);
     let right = ink.right().max(width);
     let bottom = ink.bottom().max(height);
+    let (w, h) = (right - left, bottom - top);
+    Ok((wrapped(svg, [left, top, w, h])?, size(px(w), px(h))))
+}
+
+/// `svg`'s drawing under a root viewing `[left, top, w, h]` in px.
+fn wrapped(svg: &str, [left, top, w, h]: [f32; 4]) -> Result<String, MathError> {
     let open = svg
         .find('>')
         .ok_or_else(|| MathError::said("RaTeX wrote no svg tag"))?;
     let close = svg
         .rfind("</svg>")
         .ok_or_else(|| MathError::said("RaTeX left the svg open"))?;
-    let (w, h) = (right - left, bottom - top);
-    let reframed = format!(
+    Ok(format!(
         "<svg xmlns=\"http://www.w3.org/2000/svg\" viewBox=\"{left} {top} {w} {h}\" width=\"{w}\" height=\"{h}\">{}</svg>",
         &svg[open + 1..close]
-    );
-    Ok((reframed, size(px(w), px(h))))
+    ))
 }
 
 /// The asset key for `source` at `font` in `window`.

src/typography/math/tests.rs

@@ -256,3 +256,18 @@ fn drawn_fallback_text_stays_inside_the_frame() {
         );
     }
 }
+
+#[test]
+fn a_picture_spans_its_formula_not_a_point_rescale() {
+    let formula = super::Formula {
+        source: "x^2+y^2=r^2".into(),
+        display: false,
+        rgba: 0xff,
+        font: 1600,
+        scale: 100,
+    };
+    let (_, width, _) = super::laid(&formula).expect("laid");
+    let (_, shape) = super::svg(&formula).expect("framed");
+    let ratio = shape.width.as_f32() / width;
+    assert!((0.95..1.05).contains(&ratio), "{} for {width}", shape.width);
+}