Text: stroke font space widths of the reference

The SHX names the embedded LFF fonts stand in for (txt, monotxt,
simplex, romans, romand, romanc, complex, italic, gdt, isocp) use the
space advance of the reference's fonts.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/scene/text/lff.rs

@@ -87,6 +87,22 @@ const ALIASES: &[(&str, &str)] = &[
     ("EXTFONT", "unicode"),
 ];
 
+/// The space advance of the reference's stroke fonts, in glyph units (cap
+/// height 9), measured from their text extents: the SHX names these LFF
+/// fonts stand in for keep the reference's word gaps.
+const SHX_SPACE: &[(&str, f32)] = &[
+    ("TXT", 9.0),
+    ("MONOTXT", 9.0),
+    ("SIMPLEX", 9.0 * 19.0 / 21.0),
+    ("ROMANS", 9.0),
+    ("ROMAND", 9.0),
+    ("ROMANC", 9.0),
+    ("COMPLEX", 9.0),
+    ("ITALIC", 9.0),
+    ("GDT", 9.0),
+    ("ISOCP", 3.6),
+];
+
 // ── Public types ──────────────────────────────────────────────────────────
 
 /// One glyph: a list of open 2-D polyline strokes in glyph units.
@@ -163,6 +179,12 @@ fn fonts_map() -> &'static HashMap<String, Font> {
                 map.insert(alias.to_ascii_uppercase(), f);
             }
         }
+        // Those names keep the reference font's space width.
+        for (name, word) in SHX_SPACE {
+            if let Some(f) = map.get_mut(*name) {
+                f.word_spacing = *word;
+            }
+        }
         map
     })
 }