Pick a horizontal or vertical dimension from where its text is placed (#345)

Between two points, or on a line, that don't line up with an axis, the
Sketch Dimension tool only offered the distance between them: an auto
dimension ignored where its text went. Now the placement picks what it
measures: across from the two (between the perpendiculars through them)
the distance between them, as before; past that, above or below them the
horizontal distance, beside them the vertical one. With no text, an
explicit type, or two ends already on an axis, nothing changes.

The tool previews the dimension from the cursor, so the choice follows
the pointer while placing it.

Fixes #257

Co-authored-by: Vitali M. <6042958+vitalibr@users.noreply.github.com>
Co-authored-by: bherbruck <brennen.herbruck@gmail.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

crates/ui-egui/src/dimension_create_ui_tests.rs

@@ -323,3 +323,28 @@ fn inch_dimension_entry_survives_unit_changes_undo_and_reopen() {
     assert_eq!(reopened.world_state().sketch(sketch).unwrap().sketch, before);
     crate::dim_view::cancel();
 }
+
+/// Placing the dimension of two unaligned points above them gives the horizontal distance,
+/// beside them the vertical one, and across from them the distance between them (#257).
+#[test]
+fn placing_a_two_point_dimension_picks_horizontal_vertical_or_aligned() {
+    // What each placement fixes at 10 mm: the X span, the Y span, or the length.
+    let spans = |a: solvecraft_engine::geom::Vec2, b: solvecraft_engine::geom::Vec2| [(b.x - a.x).abs(), (b.y - a.y).abs(), a.dist(b)];
+    for (at, measured) in [([6., 25.], 0), ([-10., 1.], 1), ([-5., 12.], 2)] {
+        let mut h = line([12., 16.]);
+        place(&mut h, &[[0., 0.], [12., 16.]], at);
+        type_value(&mut h, "10 mm");
+        h.step(&json!({"key":"Enter"})).unwrap();
+        assert!(!crate::dim_view::editing());
+        let state = h.app.session.world_state();
+        let sk = &state.sketch(h.app.session.active_sketch.unwrap()).unwrap().sketch;
+        let a = sk.point(sk.resolve_point("l1.start").unwrap()).unwrap();
+        let b = sk.point(sk.resolve_point("l1.end").unwrap()).unwrap();
+        let spans = spans(a, b);
+        assert!((spans[measured] - 10.0).abs() < 1e-6, "placed at {at:?}: {a:?} {b:?}");
+        // A horizontal or vertical dimension leaves the other span as drawn.
+        if measured < 2 {
+            assert!((spans[1 - measured] - [12.0, 16.0][1 - measured]).abs() < 1e-6, "placed at {at:?}: {a:?} {b:?}");
+        }
+    }
+}