CAD: right-click in a sketch offers verbs for what is selected, instead of for nothing

Select a line in a sketch, right-click, and every sketch verb was greyed: Trim,
Extend, Fillet, Chamfer, Offset, Mirror, the arrays, Constrain. The menu was
right and the selection was gone — two independent faults, each of which hid
the other.

FIRST, the Select-mode RightDown branch called clear_selection() before handing
the click back. Handing it back is correct: the m_right_consumed flag means "the
tool USED this right-click", and a plain right-click is not a gesture
terminator, so the offer should open. Clearing first is not: the offer describes
WHAT IS SELECTED, so wiping the selection guaranteed it could only ever describe
nothing. Deselection keeps its own gesture — left-click on empty space, a few
lines above in the same handler.

SECOND, offer_selection_kind() returned SkNone for every sketch state. The offer
table has always carried verbs for a selected line, arc, point or pair, but
nothing ever RETURNED those kinds, so fourteen rows were gated on selection bits
no code path could set. Classify the selection instead: SkLine / SkArc / SkPoint
/ Sk2Ent, via a first_selected_type() accessor on the tool and two forwarders on
the canvas.

Either fix alone measures as a failure — the classification is handed an empty
selection, or the preserved selection has no kind to match — which is why both
land together.

This is the second half of the report behind 3eb6e5d608: a user comparing the
Design tab with Onshape said "adding constraints seems to be missing"
(OrcaSlicer PR #15238). Constrain was one of the fourteen dead rows, and the
gesture that would have shown it threw the selection away first.

Verified at the machine on behemoth by Tommaso: select a line of a rectangle,
right-click, and the sketch verbs are live.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/slic3r/GUI/DesignCanvas.cpp

@@ -1338,6 +1338,16 @@ bool DesignCanvas::is_constraining_entities() const
     return m_sketch_tool.is_constraining_entities();
 }
 
+int DesignCanvas::sketch_selection_count() const
+{
+    return int(m_sketch_tool.selection().size());
+}
+
+bool DesignCanvas::sketch_first_selected_type(SketchEntity::Type& out) const
+{
+    return m_sketch_tool.first_selected_type(out);
+}
+
 bool DesignCanvas::selected_constrain_entities(int& e0, int& e1) const
 {
     return m_sketch_tool.selected_constrain_entities(e0, e1);

src/slic3r/GUI/DesignCanvas.hpp

@@ -261,6 +261,10 @@ public:
     // Entity-aware Constrain (Fase 4.2): pick Line entities of a committed sketch.
     void begin_constrain_entities(const std::vector<SketchEntity>& ents, const SketchPlane& plane);
     bool is_constraining_entities() const;
+    // Sketch selection, for the offer menu: how many entities are selected and what the first
+    // one is. Returns 0 when nothing is selected.
+    int  sketch_selection_count() const;
+    bool sketch_first_selected_type(SketchEntity::Type& out) const;
 
     // In-canvas bbox transform of imported Text/SVG art (replaces the Move/Scale dialog).
     void begin_imported_transform(int feat,

src/slic3r/GUI/DesignPanel.cpp

@@ -5534,8 +5534,29 @@ bool DesignPanel::sketch_map_applies() const
 // sketch_plane_from_selection, which deliberately uses m_pick_face. snaporca-3a2.)
 int DesignPanel::offer_selection_kind() const
 {
-    if (sketch_map_applies())
+    if (sketch_map_applies()) {
+        // Classify WHAT is selected in the sketch, rather than collapsing every sketch state to
+        // SkNone. The offer table has always described verbs for a selected line, arc, point or
+        // pair — Trim, Extend, Fillet, Chamfer, Offset, Mirror, the arrays, Move/Rotate/Scale,
+        // Constrain, Delete — but nothing ever RETURNED those kinds, so all thirteen were
+        // unreachable from the menu and the sketch-editing vocabulary did not exist in the one
+        // place this app tells users to look. A user comparing against Onshape reported exactly
+        // that about constraints (OrcaSlicer PR #15238).
+        const int n = m_viewport ? m_viewport->sketch_selection_count() : 0;
+        if (n >= 2) return int(OfferSel::Sk2Ent);
+        if (n == 1) {
+            SketchEntity::Type t = SketchEntity::Type::Line;
+            if (m_viewport && m_viewport->sketch_first_selected_type(t)) {
+                switch (t) {
+                case SketchEntity::Type::Line:  return int(OfferSel::SkLine);
+                case SketchEntity::Type::Point: return int(OfferSel::SkPoint);
+                // Arc, Circle, Ellipse, EllipseArc, BSpline all take the curve vocabulary.
+                default:                        return int(OfferSel::SkArc);
+                }
+            }
+        }
         return int(OfferSel::SkNone);
+    }
 
     const int nb = int(m_doc.bodies.size());
     if (m_sel_solid_vertex && m_sel_solid_body >= 0 && m_sel_solid_body < nb)

src/slic3r/GUI/DesignSketchTool.cpp

@@ -9432,11 +9432,17 @@ bool DesignSketchTool::on_mouse_impl(wxMouseEvent& evt, GLCanvas3D& canvas)
             return true;
         }
         if (evt.RightDown()) {
-            // Merely dropping a selection is not a gesture terminator: the m_right_consumed flag
-            // this return value feeds means "the tool USED this right-click", and suppressing the
-            // offer menu on a plain deselection would leave no way to reach the right-click menu
-            // again once any geometry exists. So clear, but hand the click back.
-            clear_selection();
+            // Hand the click back (return false) so the offer opens: the m_right_consumed flag
+            // this return value feeds means "the tool USED this right-click", and a plain
+            // right-click in Select mode is not a gesture terminator.
+            //
+            // But do NOT drop the selection on the way out. The offer menu describes WHAT IS
+            // SELECTED, so clearing first guaranteed it could only ever describe nothing: select
+            // a line, right-click, and the sketch verbs — Trim, Extend, Fillet, Chamfer, Offset,
+            // Mirror, the arrays, Constrain — were all greyed, because by the time the menu was
+            // built the line was no longer selected. Reported from the machine as "selected a
+            // line, right-click exit from selection: only create and reference are usable".
+            // Deselecting still has a gesture: left-click on empty space, a few lines above.
             return false;
         }
         return false;                               // let drag orbit the camera

src/slic3r/GUI/DesignSketchTool.hpp

@@ -425,6 +425,15 @@ public:
     // Selection (Mode::Select): pick points/lines/arcs/circles of the in-session
     // sketch; Shift/Ctrl extends, double-click grabs the whole connected loop.
     const std::vector<int>& selection() const { return m_selection; }
+    // Type of the first selected entity. False when nothing is selected, so the offer menu can
+    // tell a line from an arc from a point and stop collapsing every sketch selection to "none".
+    bool first_selected_type(SketchEntity::Type& out) const {
+        if (m_selection.empty()) return false;
+        const int i = m_selection.front();
+        if (i < 0 || i >= int(m_entities.size())) return false;
+        out = m_entities[i].type;
+        return true;
+    }
     void clear_selection();
     void delete_selected();                         // erase selected entities
     // Abort any pending/queued draw-then-edit value-field sequence. Removing an entity that