fix(io): a centred ATTDEF keeps its insertion point in a DWG (#2464) (#2466)

* test(io): a centred ATTDEF keeps its insertion point in a DWG (#2464)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

* fix(io): an ATTDEF with no default value is placed by its tag's width in DWG (#2464)

The writer keeps a justified text's stored insertion point only when it is near where the
baseline starts for the text's width; an ATTDEF with an empty default value has width 0, so every
AutoCAD insertion point further than half a height from the alignment point was replaced by the
alignment point. The tag is what is drawn: judge against its width.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

* fix(io): keep a stored ATTDEF point that is close to the empty text's start

The tag-width baseline check replaced a point read from a drawing whenever the
font's width of the tag put the computed start further than the allowance away,
e.g. a centred LONGTAG with group 10 at x=99.5 and group 11 at x=100 moved to
about 92.17 in DXF and DWG. A stored point close to the empty text's own start
is now kept as before; only otherwise is it judged against the tag.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

* test(io): store an ATTDEF point that differs from the computed baseline

`assert_kept(start)` stored exactly the baseline the tag-width fallback computes, so a write that replaced group 10 with that baseline passed too. The point is now 1 off the start, within the tolerance. Review of #2466.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

* test(io): an empty-value ATTDEF keeps its point with an empty or absent prompt too

The tag-width check applies to every ATTDEF with no default value, since the
CAD displays the tag whatever the prompt: the guard now says `attdef` instead
of reading as a prompt test, and the test covers a prompt, an empty one and none.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 5.5 <noreply@anthropic.com>

crates/io/src/dxf_write/common.rs

@@ -241,8 +241,19 @@ fn computed_text_insert(d: &Drawing, t: &Text) -> Vec3 {
     if q.is_finite() { Vec3::new(q.x, q.y, t.insert.z) } else { t.insert }
 }
 
+/// `attdef_prompt` is `Some` for an ATTDEF (its prompt, which may be empty) and `None` for an ATTRIB.
 pub(super) fn text_tags(w: &mut W, d: &Drawing, t: &Text, attrib: Option<(&Attrib, Version)>, attdef_prompt: Option<&str>) {
-    w.p(10, text_insert(d, t));
+    let attdef = attdef_prompt.is_some();
+    // An attribute definition with no default value is drawn as its tag, whatever its prompt: the
+    // baseline start AutoCAD stored is judged against the tag's width too. A stored point that is
+    // close to the empty text's own start is kept as it is, so the font's width of the tag never
+    // moves it.
+    let own = text_insert(d, t);
+    let insert = match attrib {
+        Some((a, _)) if attdef && t.value.is_empty() && own != t.insert => text_insert(d, &Text { value: a.tag.clone(), ..t.clone() }),
+        _ => own,
+    };
+    w.p(10, insert);
     w.f(40, t.height);
     w.s(1, &t.value);
     if t.rotation != 0.0 {
@@ -277,7 +288,7 @@ pub(super) fn text_tags(w: &mut W, d: &Drawing, t: &Text, attrib: Option<(&Attri
     }
     match attrib {
         Some((a, target)) => {
-            w.s(100, if attdef_prompt.is_some() { "AcDbAttributeDefinition" } else { "AcDbAttribute" });
+            w.s(100, if attdef { "AcDbAttributeDefinition" } else { "AcDbAttribute" });
             if target >= Version::R2010 {
                 w.i(280, 0);
             }

crates/io/tests/it/attdef_insert_dwg.rs

@@ -0,0 +1,49 @@
+//! A centre-justified ATTDEF keeps its insertion point in a DWG (#2464): AutoCAD puts it where the
+//! baseline of the displayed tag starts, which for an attribute with an empty default value is
+//! further from the alignment point than half a height.
+
+use cadcraft_doc::EntityKind;
+use cadcraft_io::{SaveOptions, Version, read, write_with};
+
+/// The `insert` x of the only ATTDEF in `d`.
+fn attdef_x(d: &cadcraft_doc::Drawing) -> f64 {
+    d.model.iter().find_map(|e| if let EntityKind::AttDef(a) = &e.kind { Some(a.text.insert.x) } else { None }).expect("an ATTDEF")
+}
+
+#[test]
+fn centred_attdef_with_an_empty_value_keeps_its_insertion_point() {
+    // The tag "LONGTAG" at height 2.5, centred on x = 100: its baseline starts half a width left.
+    // The stored point is 1 off that start (within the tolerance), so a write that recomputed
+    // it from the tag would not pass for keeping it.
+    let width = cadcraft_fonts::line_width("LONGTAG", 2.5, 1.0);
+    let start = 100.0 - width / 2.0 - 1.0;
+    assert!(100.0 - start > 3.0, "the point is well over a height from the alignment point");
+    assert_kept(start);
+}
+
+/// A stored point that a tag-width baseline would move is kept too (review of #2466): the check
+/// does not rely on the font's width of the tag, so this one is only 0.5 from the alignment point.
+#[test]
+fn centred_attdef_point_near_the_alignment_point_is_kept() {
+    assert_kept(99.5);
+}
+
+/// A centred ATTDEF with an empty default value and group 10 at `start`, group 11 at x = 100 is
+/// read from DXF and kept by a write as DXF and as DWG (both versions). The displayed text is the
+/// tag whatever the prompt: with a prompt, an empty one (group 3 empty) and none (no group 3).
+fn assert_kept(start: f64) {
+    for prompt in ["3\nprompt\n", "3\n\n", ""] {
+        let dxf = format!(
+            "0\nSECTION\n2\nENTITIES\n0\nATTDEF\n8\n0\n10\n{start}\n20\n5.0\n40\n2.5\n1\n\n7\nSTANDARD\n72\n1\n11\n100.0\n21\n5.0\n{prompt}2\nLONGTAG\n70\n8\n0\nENDSEC\n0\nEOF\n"
+        );
+        let d = read(dxf.as_bytes(), "t.dxf").unwrap();
+        assert!((attdef_x(&d) - start).abs() < 1e-6, "read from DXF");
+        let as_dxf = cadcraft_io::write(&d, "t.dxf").unwrap();
+        assert!((attdef_x(&read(&as_dxf, "t.dxf").unwrap()) - start).abs() < 1e-6, "DXF, prompt {prompt:?}: insertion point changed");
+        for version in [Version::R2000, Version::R2018] {
+            let dwg = write_with(&d, "t.dwg", &SaveOptions { version: Some(version), binary: false }).unwrap();
+            let back = read(&dwg, "t.dwg").unwrap();
+            assert!((attdef_x(&back) - start).abs() < 1e-6, "{version:?}, prompt {prompt:?}: insertion point {} instead of {start}", attdef_x(&back));
+        }
+    }
+}

crates/io/tests/it/main.rs

@@ -5,6 +5,7 @@ mod angle_header;
 mod annotative_orientation;
 mod annotative_roundtrip;
 mod assoc_array_roundtrip;
+mod attdef_insert_dwg;
 mod attrib_modes;
 mod attrib_props;
 mod block_expansion;