fix: address open PR review findings

src/entities/common.rs

@@ -110,7 +110,12 @@ pub fn format_length(value: f64) -> String {
 /// rotation leaves coordinates like -1e-15 behind, which read as `-0.0000`.
 fn without_negative_zero(text: String) -> String {
     match text.strip_prefix('-') {
-        Some(rest) if !rest.chars().any(|c| matches!(c, '1'..='9')) => rest.to_string(),
+        Some(rest)
+            if rest.chars().any(|c| c.is_ascii_digit())
+                && !rest.chars().any(|c| matches!(c, '1'..='9')) =>
+        {
+            rest.to_string()
+        }
         _ => text,
     }
 }
@@ -1276,4 +1281,10 @@ mod negative_zero_format_tests {
         assert_eq!(angle(0, 0, -45f64.to_radians()), "-45°");
         assert_eq!(angle(1, 1, -0.0001f64.to_radians()), "-0d0'0.4\"");
     }
+
+    #[test]
+    fn a_negative_infinite_value_keeps_its_sign() {
+        assert_eq!(length(2, 4, f64::NEG_INFINITY), "-inf");
+        assert_eq!(angle(0, 0, f64::NEG_INFINITY), "-inf°");
+    }
 }

src/io/obj.rs

@@ -75,7 +75,12 @@ pub fn parse_obj(src: &str, color: [f32; 4]) -> Option<MeshModel> {
     for (vi, (pos_i, norm_i)) in face_verts.iter().enumerate() {
         let pos = *positions.get(*pos_i).unwrap_or(&[0.0; 3]);
         verts.push(pos);
-        let norm = norm_i.and_then(|ni| normals_raw.get(ni).copied());
+        let norm = norm_i
+            .and_then(|ni| normals_raw.get(ni).copied())
+            .filter(|n| {
+                n.iter().all(|value| value.is_finite())
+                    && n.iter().map(|value| value * value).sum::<f32>() > 1e-12
+            });
         has_normal.push(norm.is_some());
         norms.push(norm.unwrap_or([0.0, 0.0, 0.0]));
         indices.push(vi as u32);
@@ -153,6 +158,13 @@ mod tests {
         assert_normals(&mesh.normals, [0.0, 0.0, 1.0]);
     }
 
+    #[test]
+    fn a_zero_normal_gets_the_face_normal() {
+        let src = format!("{SQUARE}vn 0 0 0\nf 1//1 2//1 3//1\n");
+        let mesh = parse_obj(&src, COLOR).expect("mesh");
+        assert_normals(&mesh.normals, [0.0, 0.0, 1.0]);
+    }
+
     /// Only the vertex with a bad index is filled; its neighbours keep theirs.
     #[test]
     fn only_the_vertex_without_a_normal_is_filled() {