Issue #56 switching how guides are created for tape measure tool

crates/benchup-app/src/construction_guide_tests.rs

@@ -140,7 +140,7 @@ fn selected_guides_render_a_distinct_highlight() {
 }
 
 #[test]
-fn tape_guide_follows_the_tape_from_an_edge_and_supports_exact_entry_and_undo() {
+fn tape_guide_from_an_edge_is_parallel_to_it_and_supports_exact_entry_and_undo() {
     let mut h = Harness::new();
     h.app
         .doc
@@ -157,14 +157,16 @@ fn tape_guide_follows_the_tape_from_an_edge_and_supports_exact_entry_and_undo()
     );
     let tape_direction = h.app.snap.unwrap().point.normalize();
     assert!(tape_direction.x > 0.1 && tape_direction.y < -0.1);
+    // Dragging away from a horizontal edge offsets a horizontal guide.
     let preview = h.app.measurement_guide().unwrap();
-    assert!(preview.direction.unwrap().distance(tape_direction) < 1e-6);
+    assert!(preview.direction.unwrap().dot(DVec3::X).abs() > 1. - 1e-6);
     h.app.length_input = "250mm".into();
     h.key(Key::Enter);
     let guide = h.app.doc.model.guides.values().next().unwrap();
-    assert!(guide.direction.unwrap().distance(tape_direction) < 1e-6);
-    assert!(guide.origin.distance(tape_direction * 0.25) < 1e-6);
-    assert!(guide.origin.cross(guide.direction.unwrap()).length() < 1e-6);
+    assert!(guide.direction.unwrap().dot(DVec3::X).abs() > 1. - 1e-6);
+    // Exact entry is the perpendicular offset from the edge.
+    assert!((guide.origin.y + 0.25).abs() < 1e-6);
+    assert!(guide.origin.z.abs() < 1e-6);
     assert_eq!(h.app.doc.model.edges, geometry.edges);
     assert_eq!(h.app.doc.model.vertices, geometry.vertices);
     assert!(h.app.doc.model.faces.is_empty());

crates/benchup-app/src/measurement_tools.rs

@@ -17,10 +17,15 @@ pub(super) struct Measurement {
 impl BenchUpApp {
     /// Use the same infinite line for the live preview and the saved guide.
     pub(super) fn measurement_guide(&self) -> Option<benchup_core::ConstructionGuide> {
-        self.measurement.as_ref()?;
+        let reference = self.measurement.as_ref()?.reference_direction;
         let points = self.measurement_points();
         let (origin, direction) = match (self.tool, points.as_slice()) {
-            (Tool::TapeMeasure, [start, end]) => (*end, (*end - *start).try_normalize()?),
+            // Like SketchUp, a tape started on an edge offsets a guide parallel
+            // to that edge; from a point it extends along the tape.
+            (Tool::TapeMeasure, [start, end]) => (
+                *end,
+                reference.or_else(|| (*end - *start).try_normalize())?,
+            ),
             (Tool::Protractor, [center, _, end]) => (*center, (*end - *center).try_normalize()?),
             _ => return None,
         };
@@ -130,7 +135,15 @@ impl BenchUpApp {
                 .copied()
                 .or(self.snap.map(|s| s.point))
                 .ok_or(tr!("measurement_tools.move_the_pointer_to_choose_a_direction_first"))?;
-            let direction = (endpoint - origin)
+            let mut tape = endpoint - origin;
+            // An edge-parallel guide is placed at the typed perpendicular offset.
+            if let Some(reference) = m.reference_direction {
+                let offset = tape - reference * tape.dot(reference);
+                if offset.length() > 1e-7 {
+                    tape = offset;
+                }
+            }
+            let direction = tape
                 .try_normalize()
                 .ok_or(tr!("measurement_tools.move_the_pointer_to_choose_a_direction_first"))?;
             Ok(origin + direction * length)