feat(ucs): align UCS Face origin and axes to nearest vertex and edge

tests/ucs_face_plane.rs

@@ -105,3 +105,74 @@ fn ucs_pick_command_enables_solid_face_picking() {
         _ => panic!("Expected CmdResult::Dispatch"),
     }
 }
+
+#[test]
+fn autocad_style_face_ucs_snaps_origin_and_aligns_axes_on_box() {
+    let box_body = solid_model::box_solid([0.0, 0.0, 0.0], 10.0, 20.0, 30.0)
+        .expect("box_solid constructs successfully");
+
+    // Top face is at Z = +15, bounds X in [-5, 5], Y in [-10, 10].
+    // Pick near corner (5, 10, 15), closer to the edge along -X than the edge along -Y.
+    let face = solid_model::nearest_planar_face(&box_body, [3.0, 9.0, 15.0])
+        .expect("top face found");
+    let ucs = solid_model::planar_face_ucs(&box_body, face, [3.0, 9.0, 15.0])
+        .expect("planar_face_ucs constructed");
+
+    // Origin must snap to the nearest corner (5, 10, 15) instead of the pick coordinate.
+    assert!((ucs.origin.x - 5.0).abs() < 1e-6);
+    assert!((ucs.origin.y - 10.0).abs() < 1e-6);
+    assert!((ucs.origin.z - 15.0).abs() < 1e-6);
+
+    // Z axis must be outward normal (0, 0, 1).
+    let z = glam::DVec3::new(ucs.x_axis.x, ucs.x_axis.y, ucs.x_axis.z)
+        .cross(glam::DVec3::new(ucs.y_axis.x, ucs.y_axis.y, ucs.y_axis.z));
+    assert!((z.z - 1.0).abs() < 1e-6);
+
+    // Closer to edge along -X: X axis must point along (-1, 0, 0).
+    assert!((ucs.x_axis.x - (-1.0)).abs() < 1e-6);
+    assert!(ucs.x_axis.y.abs() < 1e-6);
+    assert!(ucs.x_axis.z.abs() < 1e-6);
+
+    // Y axis = Z x X = (0, 0, 1) x (-1, 0, 0) = (0, -1, 0).
+    assert!(ucs.y_axis.x.abs() < 1e-6);
+    assert!((ucs.y_axis.y - (-1.0)).abs() < 1e-6);
+    assert!(ucs.y_axis.z.abs() < 1e-6);
+
+    // Now pick near the same corner (5, 10, 15), but closer to the edge along -Y.
+    let ucs_y_edge = solid_model::planar_face_ucs(&box_body, face, [4.5, 7.0, 15.0])
+        .expect("planar_face_ucs constructed");
+
+    // Origin is still the same corner (5, 10, 15).
+    assert!((ucs_y_edge.origin.x - 5.0).abs() < 1e-6);
+    assert!((ucs_y_edge.origin.y - 10.0).abs() < 1e-6);
+    assert!((ucs_y_edge.origin.z - 15.0).abs() < 1e-6);
+
+    // Closer to edge along -Y: X axis must point along (0, -1, 0).
+    assert!(ucs_y_edge.x_axis.x.abs() < 1e-6);
+    assert!((ucs_y_edge.x_axis.y - (-1.0)).abs() < 1e-6);
+    assert!(ucs_y_edge.x_axis.z.abs() < 1e-6);
+
+    // Y axis = Z x X = (0, 0, 1) x (0, -1, 0) = (1, 0, 0).
+    assert!((ucs_y_edge.y_axis.x - 1.0).abs() < 1e-6);
+    assert!(ucs_y_edge.y_axis.y.abs() < 1e-6);
+    assert!(ucs_y_edge.y_axis.z.abs() < 1e-6);
+}
+
+#[test]
+fn autocad_style_face_ucs_on_puck() {
+    let body = puck();
+    let top_face = solid_model::nearest_planar_face(&body, [60.0, -25.0, 10.0]).unwrap();
+    let ucs = solid_model::planar_face_ucs(&body, top_face, [60.0, -25.0, 10.0]).unwrap();
+
+    // Normal Z = (0, 0, 1).
+    let z = glam::DVec3::new(ucs.x_axis.x, ucs.x_axis.y, ucs.x_axis.z)
+        .cross(glam::DVec3::new(ucs.y_axis.x, ucs.y_axis.y, ucs.y_axis.z));
+    assert!((z.z - 1.0).abs() < 1e-6);
+
+    // Orthonormality of X and Y.
+    let x = glam::DVec3::new(ucs.x_axis.x, ucs.x_axis.y, ucs.x_axis.z);
+    let y = glam::DVec3::new(ucs.y_axis.x, ucs.y_axis.y, ucs.y_axis.z);
+    assert!((x.length() - 1.0).abs() < 1e-6);
+    assert!((y.length() - 1.0).abs() < 1e-6);
+    assert!(x.dot(y).abs() < 1e-6);
+}