Highlight the selected feature in the 3D scene (cyan)

Clicking a feature in the Joinery tab now highlights it in the viewport with a
cyan ghost so you can see which mortise/tenon it is; browsing candidates in the
"Fit to…" dialog highlights each one as you select it (restored to the active
feature on cancel). Reuses the overlay mechanism with a kind ("edit"=red pending
vs "highlight"=cyan); controller.highlight_feature drives it.

84 tests pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/woodshop/gui/controller.py

@@ -81,7 +81,8 @@ class Controller(QObject):
         self._schemas: str | None = None
         self.selected: list[str] = [self.scene.selection] if self.scene.selection else []
         self.active_feature: str | None = None   # feature currently being edited
-        self.preview = None                      # (Part, Feature) pending preview, or None
+        self.preview = None                      # (Part, Feature) shown as an overlay, or None
+        self.preview_kind = "edit"               # "edit" (red pending) | "highlight" (cyan)
 
     # ----- persistence / notify ----------------------------------------
     def save(self) -> None:
@@ -328,6 +329,20 @@ class Controller(QObject):
                 if val is not None and hasattr(pending, k):
                     setattr(pending, k, val)
             self.preview = (part, pending)
+            self.preview_kind = "edit"
+        self.preview_changed.emit()
+
+    def highlight_feature(self, fid: str | None) -> None:
+        """Show a cyan highlight of a feature in the scene (no edit)."""
+        if not fid:
+            self.preview = None
+        else:
+            try:
+                part, feat = self.scene.find_feature(fid)
+                self.preview = (part, copy.copy(feat))
+                self.preview_kind = "highlight"
+            except SceneError:
+                self.preview = None
         self.preview_changed.emit()
 
     def clear_preview(self) -> None:

src/woodshop/gui/feature_panel.py

@@ -123,8 +123,8 @@ class FeaturePanel(QWidget):
         self.fit_btn.setEnabled(bool(mate))
         self.fit_btn.setText(f"Fit to {mate}…" if mate else "Fit to mate…")
         self._loading = False
-        if self.c.preview is not None:   # committed state -> drop any stale ghost
-            self.c.clear_preview()
+        # Highlight the selected feature in the scene (cyan), or clear if none.
+        self.c.highlight_feature(feat.id if feat else None)
 
     def _on_row(self) -> None:
         if self._loading:
@@ -160,6 +160,9 @@ class FeaturePanel(QWidget):
             item = QListWidgetItem(label)
             item.setData(Qt.UserRole, f.id)
             lst.addItem(item)
+        # Highlight whichever candidate is selected so the user sees it in 3D.
+        lst.currentItemChanged.connect(
+            lambda cur, _prev: self.c.highlight_feature(cur.data(Qt.UserRole)) if cur else None)
         lst.setCurrentRow(0)
         lay.addWidget(lst)
         connect_cb = QCheckBox("Make connection (move && orient the other board to seat the joint)")
@@ -168,11 +171,14 @@ class FeaturePanel(QWidget):
         bb.accepted.connect(dlg.accept)
         bb.rejected.connect(dlg.reject)
         lay.addWidget(bb)
-        if dlg.exec() and lst.currentItem():
+        accepted = dlg.exec()
+        if accepted and lst.currentItem():
             target = lst.currentItem().data(Qt.UserRole)
             self.c.fit_feature(target)               # size to match
             if connect_cb.isChecked():
                 self.c.make_connection(target)        # then assemble
+        else:
+            self.c.highlight_feature(feat.id)        # restore highlight on cancel
 
 
 _HINTS = {

src/woodshop/gui/main_window.py

@@ -57,7 +57,8 @@ class MainWindow(QMainWindow):
         self.viewport.picked.connect(self._on_pick)
         self.controller.changed.connect(self._on_changed)
         self.controller.preview_changed.connect(
-            lambda: self.viewport.set_preview(self.controller.preview))
+            lambda: self.viewport.set_preview(self.controller.preview,
+                                              self.controller.preview_kind))
         self._build_menus()
         self._on_changed()  # initial render + status
 

src/woodshop/gui/viewport.py

@@ -95,8 +95,9 @@ class Viewport(QWidget):
             self.plotter.camera_position = cam  # keep the user's viewpoint
         self.plotter.render()
 
-    def set_preview(self, preview) -> None:
-        """Draw (or clear) the translucent red ghost of a pending feature edit."""
+    def set_preview(self, preview, kind="edit") -> None:
+        """Draw (or clear) a feature overlay: red for a pending edit, cyan to
+        highlight the selected feature."""
         for name in ("preview_face", "preview_edges"):
             try:
                 self.plotter.remove_actor(name)
@@ -104,13 +105,14 @@ class Viewport(QWidget):
                 pass
         if preview is not None:
             part, feat = preview
+            color = "#33ccff" if kind == "highlight" else "red"
             try:
                 mesh = feature_preview_mesh(part, feat)
-                self.plotter.add_mesh(mesh, color="red", opacity=0.4, pickable=False,
+                self.plotter.add_mesh(mesh, color=color, opacity=0.4, pickable=False,
                                       reset_camera=False, name="preview_face")
                 edges = mesh.extract_feature_edges()
                 if edges.n_points:
-                    self.plotter.add_mesh(edges, color="red", line_width=3,
+                    self.plotter.add_mesh(edges, color=color, line_width=3,
                                           pickable=False, reset_camera=False, name="preview_edges")
             except Exception:
                 pass

tests/test_gui_controller.py

@@ -113,6 +113,17 @@ def test_fit_mortise_to_tenon(tmp_path):
     assert m.depth_in == 1.5 + 1 / 32
 
 
+def test_highlight_feature(tmp_path):
+    c = _controller(tmp_path)
+    c.place("2x4", 12)
+    c.add_feature("mortise")                 # f1
+    c.highlight_feature("f1")
+    assert c.preview is not None and c.preview_kind == "highlight"
+    assert c.preview[1].id == "f1"
+    c.highlight_feature(None)
+    assert c.preview is None
+
+
 def test_unknown_tool_is_safe(tmp_path):
     c = _controller(tmp_path)
     assert "unknown" in c.execute_call("wood-bogus", {}).lower()