feat(spline): improve fit and CV editing

Keep planar conversions kernel-backed and leave unsupported 3D, CV-to-fit, and closed rebuilds unavailable instead of changing curve data.\n\nRefs #815

locales/en-US/opencadstudio.ftl

@@ -1357,6 +1357,7 @@ draw =
     .solid-specify-second-point = SOLID  Specify second point:
     .solid-specify-third-point = SOLID  Specify third point:
     .spline-specify-first-control-point = SPLINE  Specify first control point:
+    .spline-specify-first-point = SPLINE  Specify first point:
     .spline-specify-next-point-n-pts = SPLINE  Specify next point  [__ocs_arg_n__ pts]:
     .sketch = Sketch
     .start-center-angle = Start, Center, Angle
@@ -2352,6 +2353,7 @@ properties =
     .chord-x = Chord X
     .chord-y = Chord Y
     .chord-z = Chord Z
+    .chord = Chord
     .circumference = Circumference
     .class = Class
     .class-id = Class ID
@@ -2378,6 +2380,10 @@ properties =
     .control-point-x = Control Point X
     .control-point-y = Control Point Y
     .control-point-z = Control Point Z
+    .control-point-x-sentence-case = Control point X
+    .control-point-y-sentence-case = Control point Y
+    .control-point-z-sentence-case = Control point Z
+    .control-vertices = Control Vertices
     .coordination-model = Coordination Model
     .creased-edges = Creased Edges
     .croppings = Croppings
@@ -2385,6 +2391,9 @@ properties =
     .current-color-scheme = Current Color Scheme
     .current-vertex-title-case = Current Vertex
     .current-vertex-sentence-case = Current vertex
+    .current-control-point = Current Control point
+    .current-fit-point = Current Fit point
+    .cv-frame = CV frame
     .cutting-line = Cutting Line
     .dwg-payload = DWG Payload
     .dwg-version = DWG Version
@@ -2444,6 +2453,9 @@ properties =
     .end-tangent-x = End Tangent X
     .end-tangent-y = End Tangent Y
     .end-tangent-z = End Tangent Z
+    .end-tangent-vector-x = End tangent vector X
+    .end-tangent-vector-y = End tangent vector Y
+    .end-tangent-vector-z = End tangent vector Z
     .end-x = End X
     .end-y = End Y
     .end-z = End Z
@@ -2481,6 +2493,10 @@ properties =
     .fit-point-y = Fit Point Y
     .fit-point-z = Fit Point Z
     .fit-tolerance = Fit Tolerance
+    .fit-point-x-sentence-case = Fit point X
+    .fit-point-y-sentence-case = Fit point Y
+    .fit-point-z-sentence-case = Fit point Z
+    .fit-tolerance-sentence-case = Fit tolerance
     .fit-smooth-title-case = Fit/Smooth
     .fit-smooth-sentence-case = Fit/smooth
     .fixed-elevation-range = Fixed Elevation Range
@@ -2526,6 +2542,7 @@ properties =
     .jog-z = Jog Z
     .justify = Justify
     .knot-parameterization = Knot Parameterization
+    .knot-parameterization-sentence-case = Knot parameterization
     .lamp-preset = Lamp Preset
     .landing-gap = Landing Gap
     .layout-print-configuration = Layout Print Configuration
@@ -2618,6 +2635,8 @@ properties =
     .number-of-grips = Number of Grips
     .number-of-vertices = Number of Vertices
     .number-of-turns = Number of turns
+    .number-of-control-points = Number of control points
+    .number-of-fit-points = Number of fit points
     .ole-frame = OLE Frame
     .object-references = Object References
     .obliquing = Obliquing
@@ -2737,6 +2756,13 @@ properties =
     .start-tangent-x = Start Tangent X
     .start-tangent-y = Start Tangent Y
     .start-tangent-z = Start Tangent Z
+    .start-tangent-vector-x = Start tangent vector X
+    .start-tangent-vector-y = Start tangent vector Y
+    .start-tangent-vector-z = Start tangent vector Z
+    .hide = Hide
+    .periodic = Periodic
+    .square-root = Square Root
+    .uniform = Uniform
     .start-x = Start X
     .start-y = Start Y
     .start-z = Start Z

locales/tr-TR/opencadstudio.ftl

@@ -1339,6 +1339,7 @@ draw =
     .solid-specify-second-point = SOLID  İkinci noktayı belirtin:
     .solid-specify-third-point = SOLID  Üçüncü noktayı belirtin:
     .spline-specify-first-control-point = SPLINE  İlk kontrol noktasını belirtin:
+    .spline-specify-first-point = SPLINE  İlk noktayı belirtin:
     .spline-specify-next-point-n-pts = SPLINE  Sonraki noktayı belirtin [__ocs_arg_n__ nokta]:
     .sketch = Serbest Çizim
     .start-center-angle = Başlangıç, Merkez, Açı
@@ -2292,6 +2293,7 @@ properties =
     .chord-x = Kiriş X
     .chord-y = Kiriş Y
     .chord-z = Kiriş Z
+    .chord = Kiriş
     .circumference = Çevre
     .class = Sınıf
     .class-id = Sınıf Kimliği
@@ -2318,6 +2320,10 @@ properties =
     .control-point-x = Kontrol Noktası X
     .control-point-y = Kontrol Noktası Y
     .control-point-z = Kontrol Noktası Z
+    .control-point-x-sentence-case = Kontrol noktası X
+    .control-point-y-sentence-case = Kontrol noktası Y
+    .control-point-z-sentence-case = Kontrol noktası Z
+    .control-vertices = Kontrol Köşeleri
     .coordination-model = Koordinasyon Modeli
     .creased-edges = Keskin Kenarlar
     .croppings = Kırpmalar
@@ -2325,6 +2331,9 @@ properties =
     .current-color-scheme = Geçerli Renk Düzeni
     .current-vertex-title-case = Geçerli Köşe
     .current-vertex-sentence-case = Geçerli köşe
+    .current-control-point = Geçerli kontrol noktası
+    .current-fit-point = Geçerli uydurma noktası
+    .cv-frame = Kontrol çerçevesi
     .cutting-line = Kesme Çizgisi
     .dwg-payload = DWG Verisi
     .dwg-version = DWG Sürümü
@@ -2384,6 +2393,9 @@ properties =
     .end-tangent-x = Bitiş Teğeti X
     .end-tangent-y = Bitiş Teğeti Y
     .end-tangent-z = Bitiş Teğeti Z
+    .end-tangent-vector-x = Bitiş teğet vektörü X
+    .end-tangent-vector-y = Bitiş teğet vektörü Y
+    .end-tangent-vector-z = Bitiş teğet vektörü Z
     .end-x = Bitiş X
     .end-y = Bitiş Y
     .end-z = Bitiş Z
@@ -2421,6 +2433,10 @@ properties =
     .fit-point-y = Uydurma Noktası Y
     .fit-point-z = Uydurma Noktası Z
     .fit-tolerance = Uydurma Toleransı
+    .fit-point-x-sentence-case = Uydurma noktası X
+    .fit-point-y-sentence-case = Uydurma noktası Y
+    .fit-point-z-sentence-case = Uydurma noktası Z
+    .fit-tolerance-sentence-case = Uydurma toleransı
     .fit-smooth-title-case = Uydur/Yumuşat
     .fit-smooth-sentence-case = Uydur/yumuşat
     .fixed-elevation-range = Sabit Kot Aralığı
@@ -2466,6 +2482,7 @@ properties =
     .jog-z = Kırılma Z
     .justify = Hizala
     .knot-parameterization = Düğüm Parametrelemesi
+    .knot-parameterization-sentence-case = Düğüm parametrelemesi
     .lamp-preset = Lamba Ön Ayarı
     .landing-gap = Yatay Bağlantı Boşluğu
     .layout-print-configuration = Yerleşim Yazdırma Yapılandırması
@@ -2558,6 +2575,8 @@ properties =
     .number-of-grips = Tutamaç Sayısı
     .number-of-vertices = Köşe Sayısı
     .number-of-turns = Sarım sayısı
+    .number-of-control-points = Kontrol noktası sayısı
+    .number-of-fit-points = Uydurma noktası sayısı
     .ole-frame = OLE Çerçevesi
     .object-references = Nesne Referansları
     .obliquing = Eğiklik
@@ -2677,6 +2696,13 @@ properties =
     .start-tangent-x = Başlangıç Teğeti X
     .start-tangent-y = Başlangıç Teğeti Y
     .start-tangent-z = Başlangıç Teğeti Z
+    .start-tangent-vector-x = Başlangıç teğet vektörü X
+    .start-tangent-vector-y = Başlangıç teğet vektörü Y
+    .start-tangent-vector-z = Başlangıç teğet vektörü Z
+    .hide = Gizle
+    .periodic = Periyodik
+    .square-root = Karekök
+    .uniform = Eşit Aralıklı
     .start-x = Başlangıç X
     .start-y = Başlangıç Y
     .start-z = Başlangıç Z

src/app/mod.rs

@@ -82,6 +82,8 @@ pub struct GripPopup {
     pub anchor: iced::Point,
     pub items: Vec<crate::scene::model::object::GripMenuItem>,
     pub selected: usize,
+    /// Whether a click-opened menu stays visible away from its grip.
+    pub pinned: bool,
 }
 
 /// Pending follow-up value for grip-menu actions that need a number

src/app/properties.rs

@@ -121,6 +121,13 @@ impl OpenCADStudio {
                     acadrust::EntityType::LwPolyline(polyline) => Some(polyline.vertices.len()),
                     acadrust::EntityType::Polyline2D(polyline) => Some(polyline.vertices.len()),
                     acadrust::EntityType::Leader(leader) => Some(leader.vertices.len()),
+                    acadrust::EntityType::Spline(spline) => Some(
+                        if crate::entities::spline::uses_fit_method(spline) {
+                            spline.fit_points.len()
+                        } else {
+                            spline.control_points.len()
+                        },
+                    ),
                     _ => None,
                 });
             vertex_count.map_or(prop_vertex, |count| prop_vertex.min(count.saturating_sub(1)))

src/app/update/command.rs

@@ -1322,6 +1322,27 @@ pub(super) fn on_tab_close(&mut self, idx: usize) -> Task<Message> {
                     }
                 }
                 // One-shot action — apply immediately.
+                let unchanged = self.tabs[i]
+                    .scene
+                    .document
+                    .get_entity(popup.handle)
+                    .is_some_and(|entity| match (item.action, entity) {
+                        (GripMenuAction::ShowFit, acadrust::EntityType::Spline(spline)) => {
+                            !spline.cv_frame_visible
+                                && crate::entities::spline::uses_fit_method(spline)
+                        }
+                        (
+                            GripMenuAction::ShowControlVertices,
+                            acadrust::EntityType::Spline(spline),
+                        ) => {
+                            spline.cv_frame_visible
+                                || !crate::entities::spline::uses_fit_method(spline)
+                        }
+                        _ => false,
+                    });
+                if unchanged {
+                    return Task::none();
+                }
                 self.push_undo_snapshot(i, item.label);
                 // For Add Leader, the new arrow becomes the last grip; remember
                 // its id so we can grab it for placement right after.
@@ -1728,6 +1749,40 @@ pub(super) fn on_tab_close(&mut self, idx: usize) -> Task<Message> {
         let handles = self.property_target_handles(i);
 
         if !handles.is_empty() {
+            if matches!(field, "spline_method" | "knot_param" | "cv_frame") {
+                let unchanged = handles.iter().all(|handle| {
+                    let Some(acadrust::EntityType::Spline(spline)) =
+                        self.tabs[i].scene.document.get_entity(*handle)
+                    else {
+                        return false;
+                    };
+                    match field {
+                        "spline_method" => {
+                            value == if crate::entities::spline::uses_fit_method(spline) {
+                                "Fit"
+                            } else {
+                                "Control Vertices"
+                            }
+                        }
+                        "knot_param" => {
+                            let current = match spline.knot_parameterization {
+                                0 => "Chord",
+                                1 => "Square Root",
+                                2 => "Uniform",
+                                _ => "Custom",
+                            };
+                            value == current
+                        }
+                        "cv_frame" => {
+                            value == if spline.cv_frame_visible { "Show" } else { "Hide" }
+                        }
+                        _ => false,
+                    }
+                });
+                if unchanged {
+                    return Task::none();
+                }
+            }
             self.push_undo_snapshot(i, "CHPROP");
 
             if field == "vscale_std" {
@@ -2099,6 +2154,10 @@ pub(super) fn on_tab_close(&mut self, idx: usize) -> Task<Message> {
                     }
                     self.invalidate_property_targets(i, &handles);
                     self.tabs[i].dirty = true;
+                    if field == "spline_method" {
+                        self.tabs[i].properties.prop_vertex = 0;
+                        self.tabs[i].properties.prop_vertex_indicator_active = false;
+                    }
                     self.refresh_properties();
                 }
                 Task::none()
@@ -2121,6 +2180,35 @@ pub(super) fn on_tab_close(&mut self, idx: usize) -> Task<Message> {
                         } else {
                             crate::app::expr_eval::eval_to_string(&raw_val)
                         };
+                        if matches!(field, "current_fit_point" | "current_control_point") {
+                            let count = handles
+                                .iter()
+                                .filter_map(|handle| {
+                                    let entity = self.tabs[i].scene.document.get_entity(*handle)?;
+                                    match (field, entity) {
+                                        (
+                                            "current_fit_point",
+                                            acadrust::EntityType::Spline(spline),
+                                        ) => Some(spline.fit_points.len()),
+                                        (
+                                            "current_control_point",
+                                            acadrust::EntityType::Spline(spline),
+                                        ) => Some(spline.control_points.len()),
+                                        _ => None,
+                                    }
+                                })
+                                .min()
+                                .unwrap_or(0);
+                            if let Ok(requested) = val.trim().parse::<usize>() {
+                                if count > 0 {
+                                    let next = requested.clamp(1, count) - 1;
+                                    self.tabs[i].properties.prop_vertex = next;
+                                    self.tabs[i].properties.prop_vertex_indicator_active = true;
+                                }
+                            }
+                            self.refresh_properties();
+                            return Task::none();
+                        }
                         self.push_undo_snapshot(i, "CHPROP");
                         if field == "block" {
                             // Name row on a block reference: an existing name

src/app/update/viewport.rs

@@ -653,7 +653,9 @@ impl OpenCADStudio {
                         screen: p,
                         started: iced::time::Instant::now(),
                     });
-                    self.grip_popup = None;
+                    if !self.grip_popup.as_ref().is_some_and(|popup| popup.pinned) {
+                        self.grip_popup = None;
+                    }
                 } else if let Some(h) = self.grip_hover.as_mut() {
                     h.screen = p;
                 }
@@ -672,12 +674,17 @@ impl OpenCADStudio {
                         use crate::entities::traits::EntityTypeOps;
                         let items = e.grip_menu(grip_id);
                         if !items.is_empty() {
+                            let selected = items
+                                .iter()
+                                .position(|item| item.label.starts_with('✓'))
+                                .unwrap_or(0);
                             self.grip_popup = Some(crate::app::GripPopup {
                                 handle,
                                 grip_id,
                                 anchor: p,
                                 items,
-                                selected: 0,
+                                selected,
+                                pinned: false,
                             });
                         }
                     }
@@ -685,7 +692,7 @@ impl OpenCADStudio {
             }
             None => {
                 self.grip_hover = None;
-                if let Some(popup) = &self.grip_popup {
+                if let Some(popup) = self.grip_popup.as_ref().filter(|popup| !popup.pinned) {
                     let dx = p.x - popup.anchor.x;
                     let dy = p.y - popup.anchor.y;
                     if (dx * dx + dy * dy).sqrt() > POPUP_DISMISS_PX {
@@ -2736,6 +2743,32 @@ impl OpenCADStudio {
                     let Some(&handle) = self.tabs[i].selected_grip_handles.get(grip_index) else {
                         return Task::none();
                     };
+                    let grip_shape = self.tabs[i].selected_grips[grip_index].shape;
+                    if grip_shape == crate::scene::model::object::GripShape::Dropdown {
+                        use crate::entities::traits::EntityTypeOps;
+                        let items = self.tabs[i]
+                            .scene
+                            .document
+                            .get_entity(handle)
+                            .map(|entity| entity.grip_menu(grip_id))
+                            .unwrap_or_default();
+                        if !items.is_empty() {
+                            let selected = items
+                                .iter()
+                                .position(|item| item.label.starts_with('✓'))
+                                .unwrap_or(0);
+                            self.grip_popup = Some(crate::app::GripPopup {
+                                handle,
+                                grip_id,
+                                anchor: p_full,
+                                items,
+                                selected,
+                                pinned: true,
+                            });
+                        }
+                        self.grip_hover = None;
+                        return Task::none();
+                    }
                     // The visibility (lookup) grip opens a state
                     // dropdown instead of starting a stretch drag.
                     if grip_id == crate::app::visibility::VIS_GRIP_ID {

src/app/view/mod.rs

@@ -414,22 +414,24 @@ impl OpenCADStudio {
                         None => tab.scene.active_model_tile_bounds(vw, vh),
                     };
                     let sel_h = tab.selected_handle;
-                    // The Current Vertex the Properties panel is focused on:
-                    // mark that grip hot so the navigated vertex is visible in
-                    // the drawing. Only for a single selected polyline, whose
-                    // vertex grips are ids 0..n. (Properties vertex stepper)
+                    // Mark the Properties panel's current point grip hot.
                     let current_vertex_grip: Option<usize> = tab
                         .properties
                         .prop_vertex_indicator_active
                         .then(|| sel_h)
                         .flatten()
                         .and_then(|h| {
-                        matches!(
-                            tab.scene.document.get_entity(h),
-                            Some(acadrust::EntityType::LwPolyline(_))
-                                | Some(acadrust::EntityType::Polyline2D(_))
-                        )
-                        .then_some(tab.properties.prop_vertex)
+                            let indexed = match tab.scene.document.get_entity(h) {
+                                Some(acadrust::EntityType::LwPolyline(_))
+                                | Some(acadrust::EntityType::Polyline2D(_)) => true,
+                                Some(acadrust::EntityType::Spline(spline)) => {
+                                    !crate::entities::spline::uses_fit_method(spline)
+                                        || !spline.cv_frame_visible
+                                        || crate::entities::curve::spline_curve(spline).is_none()
+                                }
+                                _ => false,
+                            };
+                            indexed.then_some(tab.properties.prop_vertex)
                         });
                     // In-viewport grips are model-space; project them with the
                     // viewport camera so they sit on the wire the GPU draws.
@@ -495,6 +497,30 @@ impl OpenCADStudio {
                 } else {
                     vec![]
                 };
+            let control_polygon = tab.selected_handle.and_then(|handle| {
+                let spline = match tab.scene.document.get_entity(handle) {
+                    Some(acadrust::EntityType::Spline(spline)) if spline.cv_frame_visible => spline,
+                    _ => return None,
+                };
+                if tab
+                    .selected_grip_handles
+                    .iter()
+                    .any(|owner| *owner != handle)
+                {
+                    return None;
+                }
+                let points: Vec<_> = grips
+                    .iter()
+                    .filter(|grip| {
+                        grip.shape == crate::scene::model::object::GripShape::Circle
+                    })
+                    .map(|grip| grip.pos)
+                    .collect();
+                (points.len() >= 2).then_some((
+                    points,
+                    spline.flags.closed || spline.flags.periodic,
+                ))
+            });
             let grip_clip = if grips.is_empty() {
                 None
             } else {
@@ -688,6 +714,7 @@ impl OpenCADStudio {
                 snap_ext_base,
                 snap_ext_base2,
                 grips,
+                control_polygon,
                 grip_clip,
                 ucs_icons,
                 ost_points,
@@ -1092,26 +1119,28 @@ impl OpenCADStudio {
             }
         }
 
-        // Multi-functional grip popup (Phase 2). One bordered container
-        // wraps a column of borderless item buttons so the popup reads
-        // as a single widget instead of stacked tiles.
         if let Some(popup) = self.grip_popup.as_ref() {
             if !tab.is_start {
-                // Size the row to the widest label so the selection
-                // highlight fills the whole row instead of just the
-                // text glyphs. ~7 px per character at size 12 + the
-                // horizontal padding (10 + 10).
-                let max_len = popup
+                let labels: Vec<String> = popup
                     .items
                     .iter()
-                    .map(|i| i.label.chars().count())
+                    .map(|item| {
+                        let (mark, raw) = item
+                            .label
+                            .strip_prefix("✓ ")
+                            .map_or(("", item.label), |raw| ("✓ ", raw));
+                        format!("{mark}{}", crate::i18n::translate(raw))
+                    })
+                    .collect();
+                let max_len = labels
+                    .iter()
+                    .map(|label| label.chars().count())
                     .max()
                     .unwrap_or(8) as f32;
                 let row_w = max_len * 7.0 + 24.0;
                 let mut col = column![].spacing(0).width(iced::Length::Fixed(row_w));
-                for (idx, item) in popup.items.iter().enumerate() {
+                for (idx, label) in labels.into_iter().enumerate() {
                     let is_sel = idx == popup.selected;
-                    let label = item.label;
                     let btn = button(text(label).size(12))
                         .on_press(Message::GripMenuPick(idx))
                         .padding([3, 10])

src/entities/common.rs

@@ -453,6 +453,30 @@ pub fn circle_grip(id: usize, world: glam::DVec3) -> GripDef {
     }
 }
 
+/// Round grip that edits one vertex.
+pub fn round_grip(id: usize, world: glam::DVec3) -> GripDef {
+    GripDef {
+        id,
+        world,
+        is_midpoint: false,
+        shape: GripShape::Circle,
+        dir: None,
+        axis: None,
+    }
+}
+
+/// Screen-offset down-arrow that opens a choice menu for an entity.
+pub fn dropdown_grip(id: usize, world: glam::DVec3) -> GripDef {
+    GripDef {
+        id,
+        world,
+        is_midpoint: false,
+        shape: GripShape::Dropdown,
+        dir: None,
+        axis: None,
+    }
+}
+
 /// Mid-segment stretch grip oriented along `dir` (the segment's in-plane
 /// world-XY direction). Drawn as a small rectangle elongated along the
 /// segment so the affordance reads as "stretch perpendicular".

src/entities/curve.rs

@@ -287,12 +287,12 @@ pub fn polyline2d_curve(polyline: &Polyline2D) -> Option<PlanarCurve> {
 /// plane the normal describes. A spline that genuinely wanders in space gets
 /// `None`, which is honest: flattening it to XY would move it.
 pub fn spline_curve(spline: &SplineEnt) -> Option<PlanarCurve> {
-    let points: Vec<Vector3> = spline
-        .control_points
-        .iter()
-        .chain(spline.fit_points.iter())
-        .copied()
-        .collect();
+    let source = if crate::entities::spline::uses_fit_method(spline) {
+        &spline.fit_points
+    } else {
+        &spline.control_points
+    };
+    let points: Vec<Vector3> = source.to_vec();
     let first = points.first()?;
     let normal = normalized(spline.normal);
     let elevation = Vec3::from(xyz(*first)).dot(Vec3::from(xyz(normal)));

src/entities/spline.rs

@@ -1,12 +1,20 @@
 use acadrust::entities::Spline;
 use crate::t;
+use cadkernel::geom2d::Curve as KernelCurve;
 use cadkernel::space::NurbsCurve3;
 
 use crate::command::EntityTransform;
-use crate::entities::common::{edit_prop as edit, parse_f64, ro_prop as ro, square_grip};
+use crate::entities::common::{
+    dropdown_grip, edit_prop as edit, parse_f64, ro_prop as ro, round_grip, square_grip,
+};
 use crate::entities::traits::RenderConvertible;
 use crate::scene::convert::acad_to_render::{RenderEntity, RenderObject};
-use crate::scene::model::object::{GripApply, GripDef, PropSection};
+use crate::scene::model::object::{GripApply, GripDef, PropSection, PropValue, Property};
+
+pub(crate) fn uses_fit_method(spline: &Spline) -> bool {
+    let degree = spline.degree.max(1) as usize;
+    !spline.fit_points.is_empty() && spline.control_points.len() <= degree
+}
 
 fn to_render(spl: &Spline) -> RenderEntity {
     let n = spl.control_points.len();
@@ -86,22 +94,24 @@ fn to_render(spl: &Spline) -> RenderEntity {
     let (snap_pts, key_vertices) = match curve_snap {
         Some(snap) => {
             let mut points = snap.snap_pts;
-            points.extend(spl.fit_points.iter().map(|p| {
-                (
-                    glam::DVec3::new(p.x, p.y, p.z),
-                    crate::scene::model::wire_model::SnapHint::Endpoint,
-                )
-            }));
+            if uses_fit_method(spl) {
+                points.extend(spl.fit_points.iter().map(|p| {
+                    (
+                        glam::DVec3::new(p.x, p.y, p.z),
+                        crate::scene::model::wire_model::SnapHint::Endpoint,
+                    )
+                }));
+            }
             (points, Vec::new())
         }
         // A spline through points in space is not a planar curve, so the
         // kernel has nothing to say about it. Its stored points remain the
         // only thing to offer.
         None => {
-            let source = if spl.fit_points.is_empty() {
-                &spl.control_points
-            } else {
+            let source = if uses_fit_method(spl) {
                 &spl.fit_points
+            } else {
+                &spl.control_points
             };
             (
                 Vec::new(),
@@ -141,10 +151,9 @@ fn to_render(spl: &Spline) -> RenderEntity {
 }
 
 pub(crate) fn measurement_polyline(spl: &Spline) -> Vec<[f64; 3]> {
-    let count = spl.control_points.len();
-    if count < 2 {
+    if uses_fit_method(spl) {
         if spl.fit_points.len() < 2 {
-            return spl.control_points.iter().map(|p| [p.x, p.y, p.z]).collect();
+            return spl.fit_points.iter().map(|p| [p.x, p.y, p.z]).collect();
         }
         return if spl.flags.closed || spl.flags.periodic {
             catmull_rom_polyline(&spl.fit_points, true)
@@ -153,6 +162,11 @@ pub(crate) fn measurement_polyline(spl: &Spline) -> Vec<[f64; 3]> {
         };
     }
 
+    let count = spl.control_points.len();
+    if count < 2 {
+        return spl.control_points.iter().map(|p| [p.x, p.y, p.z]).collect();
+    }
+
     let degree = spl.degree.max(0) as usize;
     if degree == 0 || degree >= count {
         return spl.control_points.iter().map(|p| [p.x, p.y, p.z]).collect();
@@ -261,6 +275,60 @@ fn fit_spline_polyline(spl: &Spline) -> Vec<[f64; 3]> {
         return p;
     }
 
+    let Some((h, slopes)) = fit_spline_slopes(spl, &p) else {
+        return p;
+    };
+
+    // Evaluate each segment as a cubic Hermite (dP/du = slope · h_i).
+    let mut out = Vec::new();
+    for i in 0..n - 1 {
+        let point_at = |u: f64| {
+            let (u2, u3) = (u * u, u * u * u);
+            let h00 = 2.0 * u3 - 3.0 * u2 + 1.0;
+            let h10 = u3 - 2.0 * u2 + u;
+            let h01 = -2.0 * u3 + 3.0 * u2;
+            let h11 = u3 - u2;
+            let mut q = [0.0f64; 3];
+            for k in 0..3 {
+                let m0 = slopes[k][i] * h[i];
+                let m1 = slopes[k][i + 1] * h[i];
+                q[k] = h00 * p[i][k] + h10 * m0 + h01 * p[i + 1][k] + h11 * m1;
+            }
+            q
+        };
+        let tangent_at = |u: f64| {
+            let u2 = u * u;
+            let (h00, h10, h01, h11) = (
+                6.0 * u2 - 6.0 * u,
+                3.0 * u2 - 4.0 * u + 1.0,
+                -6.0 * u2 + 6.0 * u,
+                3.0 * u2 - 2.0 * u,
+            );
+            let mut q = [0.0; 3];
+            for k in 0..3 {
+                let m0 = slopes[k][i] * h[i];
+                let m1 = slopes[k][i + 1] * h[i];
+                q[k] = h00 * p[i][k] + h10 * m0 + h01 * p[i + 1][k] + h11 * m1;
+            }
+            q
+        };
+        let sampled = cadkernel::tessellation::sample_curve3_angle(
+            point_at,
+            tangent_at,
+            cadkernel::tessellation::DEFAULT_ANGLE,
+        );
+        out.extend(sampled.into_iter().skip(usize::from(i > 0)));
+    }
+    out
+}
+
+/// Slopes used by spatial fit interpolation.
+fn fit_spline_slopes(spl: &Spline, p: &[[f64; 3]]) -> Option<(Vec<f64>, [Vec<f64>; 3])> {
+    let n = p.len();
+    if n < 2 {
+        return None;
+    }
+
     // Parameterise the fit points (unnormalised, so a unit end tangent — how the
     // tangents are stored — is a consistent dP/dt). Match the spline's knot
     // parameterisation: 2 = uniform, 1 = centripetal (√chord), else chord.
@@ -329,48 +397,7 @@ fn fit_spline_polyline(spl: &Spline) -> Vec<[f64; 3]> {
         thomas_solve(&a, &b, &c, &mut d);
         slopes[k] = d;
     }
-
-    // Evaluate each segment as a cubic Hermite (dP/du = slope · h_i).
-    let mut out = Vec::new();
-    for i in 0..n - 1 {
-        let point_at = |u: f64| {
-            let (u2, u3) = (u * u, u * u * u);
-            let h00 = 2.0 * u3 - 3.0 * u2 + 1.0;
-            let h10 = u3 - 2.0 * u2 + u;
-            let h01 = -2.0 * u3 + 3.0 * u2;
-            let h11 = u3 - u2;
-            let mut q = [0.0f64; 3];
-            for k in 0..3 {
-                let m0 = slopes[k][i] * h[i];
-                let m1 = slopes[k][i + 1] * h[i];
-                q[k] = h00 * p[i][k] + h10 * m0 + h01 * p[i + 1][k] + h11 * m1;
-            }
-            q
-        };
-        let tangent_at = |u: f64| {
-            let u2 = u * u;
-            let (h00, h10, h01, h11) = (
-                6.0 * u2 - 6.0 * u,
-                3.0 * u2 - 4.0 * u + 1.0,
-                -6.0 * u2 + 6.0 * u,
-                3.0 * u2 - 2.0 * u,
-            );
-            let mut q = [0.0; 3];
-            for k in 0..3 {
-                let m0 = slopes[k][i] * h[i];
-                let m1 = slopes[k][i + 1] * h[i];
-                q[k] = h00 * p[i][k] + h10 * m0 + h01 * p[i + 1][k] + h11 * m1;
-            }
-            q
-        };
-        let sampled = cadkernel::tessellation::sample_curve3_angle(
-            point_at,
-            tangent_at,
-            cadkernel::tessellation::DEFAULT_ANGLE,
-        );
-        out.extend(sampled.into_iter().skip(usize::from(i > 0)));
-    }
-    out
+    Some((h, slopes))
 }
 
 /// In-place Thomas solve for a tridiagonal system (`a` sub-, `b` main-, `c`
@@ -390,189 +417,482 @@ fn thomas_solve(a: &[f64], b: &[f64], c: &[f64], d: &mut [f64]) {
     }
 }
 
-fn grips(spline: &Spline) -> Vec<GripDef> {
-    // A fit-point spline carries no control points, so its editable points — and
-    // therefore its grips — are the fit points it interpolates. A CV spline
-    // grips its control vertices.
-    let source = if spline.control_points.is_empty() {
-        &spline.fit_points
-    } else {
-        &spline.control_points
+pub(crate) const SPLINE_MODE_GRIP_ID: usize = usize::MAX - 1;
+
+fn control_vertices(spline: &Spline) -> Vec<acadrust::types::Vector3> {
+    if !uses_fit_method(spline) {
+        return spline.control_points.clone();
+    }
+    let Some(planar) = crate::entities::curve::spline_curve(spline) else {
+        return Vec::new();
     };
-    source
+    let KernelCurve::Nurbs(curve) = &planar.curve else {
+        return Vec::new();
+    };
+    curve
+        .control_points()
         .iter()
-        .enumerate()
-        .map(|(i, p)| square_grip(i, glam::DVec3::new(p.x, p.y, p.z)))
+        .map(|point| {
+            let point = planar.plane.point_at(*point);
+            acadrust::types::Vector3::new(point[0], point[1], point[2])
+        })
         .collect()
 }
 
-fn properties(spline: &Spline) -> Vec<PropSection> {
-    let show = if spline.fit_points.is_empty() {
-        "Control Vertices"
-    } else {
-        "Fit Points"
-    };
-    let cp0 = spline.control_points.first();
-    let fp0 = spline.fit_points.first();
-    let w0 = spline.weights.first().copied();
+fn choice_prop(
+    label: &str,
+    field: &'static str,
+    selected: &str,
+    options: &[&str],
+) -> Property {
+    Property {
+        label: label.into(),
+        field,
+        value: PropValue::Choice {
+            selected: selected.to_string(),
+            options: options.iter().map(|option| option.to_string()).collect(),
+        },
+    }
+}
 
-    // Polyline-approximation length over the effective defining points.
-    let pts = if spline.fit_points.is_empty() {
-        &spline.control_points
-    } else {
-        &spline.fit_points
+fn index_prop(label: &str, field: &'static str, index: usize, count: usize) -> Property {
+    Property {
+        label: label.into(),
+        field,
+        value: PropValue::EditText(if count == 0 {
+            "0".to_string()
+        } else {
+            (index + 1).to_string()
+        }),
+    }
+}
+
+fn convert_to_control_method(spline: &mut Spline) -> bool {
+    if !uses_fit_method(spline) {
+        return true;
+    }
+    let Some(planar) = crate::entities::curve::spline_curve(spline) else {
+        return false;
     };
-    let mut length = 0.0;
-    for w in pts.windows(2) {
-        let dx = w[1].x - w[0].x;
-        let dy = w[1].y - w[0].y;
-        let dz = w[1].z - w[0].z;
-        length += (dx * dx + dy * dy + dz * dz).sqrt();
+    let KernelCurve::Nurbs(curve) = &planar.curve else {
+        return false;
+    };
+    spline.degree = curve.degree() as i32;
+    spline.knots = curve.knots().to_vec();
+    spline.control_points = curve
+        .control_points()
+        .iter()
+        .map(|point| {
+            let point = planar.plane.point_at(*point);
+            acadrust::types::Vector3::new(point[0], point[1], point[2])
+        })
+        .collect();
+    spline.weights = if curve.is_rational() {
+        curve.weights().to_vec()
+    } else {
+        Vec::new()
+    };
+    spline.flags.rational = curve.is_rational();
+    spline.flags.planar = true;
+    spline.fit_points.clear();
+    spline.begin_tangent = acadrust::types::Vector3::ZERO;
+    spline.end_tangent = acadrust::types::Vector3::ZERO;
+    true
+}
+
+fn convert_to_fit_method(spline: &mut Spline) -> bool {
+    uses_fit_method(spline)
+}
+
+fn is_planar(spline: &Spline) -> bool {
+    crate::entities::curve::spline_curve(spline).is_some()
+}
+
+fn tangent_is_set(tangent: &acadrust::types::Vector3) -> bool {
+    tangent.x * tangent.x + tangent.y * tangent.y + tangent.z * tangent.z > 1e-18
+}
+
+/// Stored or kernel-derived fit-curve end tangents.
+fn effective_fit_tangents(
+    spline: &Spline,
+) -> (acadrust::types::Vector3, acadrust::types::Vector3) {
+    let begin_set = tangent_is_set(&spline.begin_tangent);
+    let end_set = tangent_is_set(&spline.end_tangent);
+    if begin_set && end_set {
+        return (spline.begin_tangent, spline.end_tangent);
     }
 
-    let closed = spline.flags.closed || spline.flags.periodic;
-    let yes_no = |b: bool| if b { "Yes" } else { "No" };
+    let derived = crate::entities::curve::spline_curve(spline).and_then(|planar| {
+        let KernelCurve::Nurbs(curve) = &planar.curve else {
+            return None;
+        };
+        let (start, end) = curve.domain();
+        Some((
+            planar.plane.vector_at(curve.derivative_at_knot(start)),
+            planar.plane.vector_at(curve.derivative_at_knot(end)),
+        ))
+    });
 
-    // Knot parameterization method (R2013+ DWG); older splines report 0.
+    let Some((derived_begin, derived_end)) = derived else {
+        return (spline.begin_tangent, spline.end_tangent);
+    };
+    let vector = |value: [f64; 3]| {
+        acadrust::types::Vector3::new(value[0], value[1], value[2])
+    };
+    (
+        if begin_set {
+            spline.begin_tangent
+        } else {
+            vector(derived_begin)
+        },
+        if end_set {
+            spline.end_tangent
+        } else {
+            vector(derived_end)
+        },
+    )
+}
+
+fn grips(spline: &Spline) -> Vec<GripDef> {
+    let fit_method = uses_fit_method(spline);
+    let derived_control = control_vertices(spline);
+    let show_control_vertices = (spline.cv_frame_visible || !fit_method)
+        && derived_control.len() >= 2;
+    let source = if show_control_vertices {
+        derived_control
+    } else if fit_method {
+        spline.fit_points.clone()
+    } else {
+        spline.control_points.clone()
+    };
+    let mut grips: Vec<_> = source
+        .iter()
+        .enumerate()
+        .map(|(i, p)| {
+            let world = glam::DVec3::new(p.x, p.y, p.z);
+            if show_control_vertices {
+                round_grip(i, world)
+            } else {
+                square_grip(i, world)
+            }
+        })
+        .collect();
+    if let Some(first) = source.first() {
+        grips.push(dropdown_grip(
+            SPLINE_MODE_GRIP_ID,
+            glam::DVec3::new(first.x, first.y, first.z),
+        ));
+    }
+    grips
+}
+
+fn properties(spline: &Spline) -> Vec<PropSection> {
+    let fit_method = uses_fit_method(spline);
+    let method = if fit_method { "Fit" } else { "Control Vertices" };
+    let closed = spline.flags.closed || spline.flags.periodic;
+    let can_show_control = control_vertices(spline).len() >= 2;
+    let yes_no = |b: bool| if b { "Yes" } else { "No" };
     let knot_param = match spline.knot_parameterization {
         0 => "Chord",
         1 => "Square Root",
         2 => "Uniform",
+        15 => "Custom",
         _ => "Custom",
     };
-
-    // Closed splines enclose an area; approximate it with the shoelace
-    // formula over the defining points projected to the XY plane, matching
-    // the polyline approximation already used for Length.
-    let area = if closed && pts.len() >= 3 {
-        let mut acc = 0.0;
-        for w in pts.windows(2) {
-            acc += w[0].x * w[1].y - w[1].x * w[0].y;
-        }
-        if let (Some(first), Some(last)) = (pts.first(), pts.last()) {
-            acc += last.x * first.y - first.x * last.y;
-        }
-        format!("{:.4}", acc.abs() * 0.5)
+    let current = crate::scene::view::dispatch::prop_current_vertex();
+    let (effective_begin_tangent, effective_end_tangent) = effective_fit_tangents(spline);
+    let mut data_points = if fit_method {
+        let count = spline.fit_points.len();
+        let index = current.min(count.saturating_sub(1));
+        let point = spline.fit_points.get(index);
+        vec![
+            ro(
+                t!("Number of fit points").as_ref(),
+                "fit_pt_count",
+                count.to_string(),
+            ),
+            index_prop(
+                t!("Current Fit point").as_ref(),
+                "current_fit_point",
+                index,
+                count,
+            ),
+            edit(
+                t!("Fit point X").as_ref(),
+                "fit_pt_x",
+                point.map(|value| value.x).unwrap_or(0.0),
+            ),
+            edit(
+                t!("Fit point Y").as_ref(),
+                "fit_pt_y",
+                point.map(|value| value.y).unwrap_or(0.0),
+            ),
+            edit(
+                t!("Fit point Z").as_ref(),
+                "fit_pt_z",
+                point.map(|value| value.z).unwrap_or(0.0),
+            ),
+            if matches!(spline.knot_parameterization, 0..=2) {
+                choice_prop(
+                    t!("Knot parameterization").as_ref(),
+                    "knot_param",
+                    knot_param,
+                    &["Chord", "Square Root", "Uniform"],
+                )
+            } else {
+                ro(
+                    t!("Knot parameterization").as_ref(),
+                    "knot_param",
+                    crate::i18n::translate(knot_param).into_owned(),
+                )
+            },
+        ]
     } else {
-        String::new()
+        let count = spline.control_points.len();
+        let index = current.min(count.saturating_sub(1));
+        let point = spline.control_points.get(index);
+        let weight = spline.weights.get(index).copied().unwrap_or(1.0);
+        vec![
+            ro(
+                t!("Number of control points").as_ref(),
+                "ctrl_pt_count",
+                count.to_string(),
+            ),
+            index_prop(
+                t!("Current Control point").as_ref(),
+                "current_control_point",
+                index,
+                count,
+            ),
+            edit(
+                t!("Control point X").as_ref(),
+                "ctrl_pt_x",
+                point.map(|value| value.x).unwrap_or(0.0),
+            ),
+            edit(
+                t!("Control point Y").as_ref(),
+                "ctrl_pt_y",
+                point.map(|value| value.y).unwrap_or(0.0),
+            ),
+            edit(
+                t!("Control point Z").as_ref(),
+                "ctrl_pt_z",
+                point.map(|value| value.z).unwrap_or(0.0),
+            ),
+            edit(t!("Weight").as_ref(), "weight", weight),
+        ]
     };
+    data_points.push(if can_show_control {
+        choice_prop(
+            t!("CV frame").as_ref(),
+            "cv_frame",
+            if spline.cv_frame_visible { "Show" } else { "Hide" },
+            &["Hide", "Show"],
+        )
+    } else {
+        ro(t!("CV frame").as_ref(), "cv_frame", t!("Hide").into_owned())
+    });
+
+    let method_prop = if fit_method && can_show_control {
+        choice_prop(
+            t!("Method").as_ref(),
+            "spline_method",
+            method,
+            &["Fit", "Control Vertices"],
+        )
+    } else {
+        ro(
+            t!("Method").as_ref(),
+            "spline_method",
+            crate::i18n::translate(method).into_owned(),
+        )
+    };
+    let mut misc = vec![
+        method_prop,
+        ro(t!("Degree").as_ref(), "degree", spline.degree.to_string()),
+        ro(
+            t!("Closed").as_ref(),
+            "closed",
+            crate::i18n::translate(yes_no(closed)).into_owned(),
+        ),
+        ro(
+            t!("Periodic").as_ref(),
+            "periodic",
+            crate::i18n::translate(yes_no(spline.flags.periodic)).into_owned(),
+        ),
+        ro(
+            t!("Planar").as_ref(),
+            "planar",
+            crate::i18n::translate(yes_no(is_planar(spline))).into_owned(),
+        ),
+    ];
+    if fit_method {
+        misc.extend([
+            edit(
+                t!("Start tangent vector X").as_ref(),
+                "start_tan_x",
+                effective_begin_tangent.x,
+            ),
+            edit(
+                t!("Start tangent vector Y").as_ref(),
+                "start_tan_y",
+                effective_begin_tangent.y,
+            ),
+            edit(
+                t!("Start tangent vector Z").as_ref(),
+                "start_tan_z",
+                effective_begin_tangent.z,
+            ),
+            edit(
+                t!("End tangent vector X").as_ref(),
+                "end_tan_x",
+                effective_end_tangent.x,
+            ),
+            edit(
+                t!("End tangent vector Y").as_ref(),
+                "end_tan_y",
+                effective_end_tangent.y,
+            ),
+            edit(
+                t!("End tangent vector Z").as_ref(),
+                "end_tan_z",
+                effective_end_tangent.z,
+            ),
+            edit(
+                t!("Fit tolerance").as_ref(),
+                "fit_tolerance",
+                spline.fit_tolerance,
+            ),
+        ]);
+    }
 
     vec![
         PropSection {
             title: t!("Data Points").into_owned(),
-            props: vec![
-                ro(t!("Show").as_ref(), "show", show),
-                ro(t!("Degree").as_ref(), "degree", spline.degree.to_string()),
-                ro(
-                    t!("Control Point Count").as_ref(),
-                    "ctrl_pt_count",
-                    spline.control_points.len().to_string(),
-                ),
-                ro(t!("Control Point").as_ref(), "ctrl_pt_index", "0"),
-                edit(
-                    t!("Control Point X").as_ref(),
-                    "ctrl_pt_x",
-                    cp0.map(|p| p.x).unwrap_or(0.0),
-                ),
-                edit(
-                    t!("Control Point Y").as_ref(),
-                    "ctrl_pt_y",
-                    cp0.map(|p| p.y).unwrap_or(0.0),
-                ),
-                edit(
-                    t!("Control Point Z").as_ref(),
-                    "ctrl_pt_z",
-                    cp0.map(|p| p.z).unwrap_or(0.0),
-                ),
-                edit(t!("Weight").as_ref(), "weight", w0.unwrap_or(1.0)),
-                ro(t!("Knot Parameterization").as_ref(), "knot_param", knot_param),
-                ro(
-                    t!("Fit Point Count").as_ref(),
-                    "fit_pt_count",
-                    spline.fit_points.len().to_string(),
-                ),
-                ro(t!("Fit Point").as_ref(), "fit_pt_index", "0"),
-                edit(t!("Fit Point X").as_ref(), "fit_pt_x", fp0.map(|p| p.x).unwrap_or(0.0)),
-                edit(t!("Fit Point Y").as_ref(), "fit_pt_y", fp0.map(|p| p.y).unwrap_or(0.0)),
-                edit(t!("Fit Point Z").as_ref(), "fit_pt_z", fp0.map(|p| p.z).unwrap_or(0.0)),
-                edit(t!("Fit Tolerance").as_ref(), "fit_tolerance", spline.fit_tolerance),
-                edit(t!("Start Tangent X").as_ref(), "start_tan_x", spline.begin_tangent.x),
-                edit(t!("Start Tangent Y").as_ref(), "start_tan_y", spline.begin_tangent.y),
-                edit(t!("Start Tangent Z").as_ref(), "start_tan_z", spline.begin_tangent.z),
-                edit(t!("End Tangent X").as_ref(), "end_tan_x", spline.end_tangent.x),
-                edit(t!("End Tangent Y").as_ref(), "end_tan_y", spline.end_tangent.y),
-                edit(t!("End Tangent Z").as_ref(), "end_tan_z", spline.end_tangent.z),
-            ],
+            props: data_points,
         },
         PropSection {
             title: t!("Misc").into_owned(),
-            props: vec![
-                ro(t!("Closed").as_ref(), "closed", yes_no(closed)),
-                ro(t!("Planar").as_ref(), "planar", yes_no(spline.flags.planar)),
-                ro(t!("Length").as_ref(), "length", format!("{length:.4}")),
-                ro(t!("Area").as_ref(), "area", area),
-            ],
+            props: misc,
         },
     ]
 }
 
 fn apply_geom_prop(spline: &mut Spline, field: &str, value: &str) {
+    match field {
+        "spline_method" => {
+            if value == "Control Vertices" {
+                convert_to_control_method(spline);
+            }
+            return;
+        }
+        "knot_param" => {
+            spline.knot_parameterization = match value {
+                "Chord" => 0,
+                "Square Root" => 1,
+                "Uniform" => 2,
+                _ => return,
+            };
+            return;
+        }
+        "cv_frame" => {
+            spline.cv_frame_visible = value == "Show" && control_vertices(spline).len() >= 2;
+            return;
+        }
+        _ => {}
+    }
+    let (effective_begin_tangent, effective_end_tangent) = effective_fit_tangents(spline);
     let Some(v) = parse_f64(value) else { return };
+    let control_index = crate::scene::view::dispatch::prop_current_vertex()
+        .min(spline.control_points.len().saturating_sub(1));
+    let fit_index = crate::scene::view::dispatch::prop_current_vertex()
+        .min(spline.fit_points.len().saturating_sub(1));
     match field {
         "ctrl_pt_x" => {
-            if let Some(cp) = spline.control_points.first_mut() {
+            if let Some(cp) = spline.control_points.get_mut(control_index) {
                 cp.x = v;
             }
         }
         "ctrl_pt_y" => {
-            if let Some(cp) = spline.control_points.first_mut() {
+            if let Some(cp) = spline.control_points.get_mut(control_index) {
                 cp.y = v;
             }
         }
         "ctrl_pt_z" => {
-            if let Some(cp) = spline.control_points.first_mut() {
+            if let Some(cp) = spline.control_points.get_mut(control_index) {
                 cp.z = v;
             }
         }
         "weight" => {
-            if let Some(w) = spline.weights.first_mut() {
-                *w = v;
+            if v > 0.0 && !spline.control_points.is_empty() {
+                if spline.weights.len() != spline.control_points.len() {
+                    spline.weights = vec![1.0; spline.control_points.len()];
+                }
+                spline.weights[control_index] = v;
+                spline.flags.rational = spline
+                    .weights
+                    .iter()
+                    .any(|weight| (*weight - spline.weights[0]).abs() > 1e-12);
             }
         }
         "fit_pt_x" => {
-            if let Some(fp) = spline.fit_points.first_mut() {
+            if let Some(fp) = spline.fit_points.get_mut(fit_index) {
                 fp.x = v;
             }
         }
         "fit_pt_y" => {
-            if let Some(fp) = spline.fit_points.first_mut() {
+            if let Some(fp) = spline.fit_points.get_mut(fit_index) {
                 fp.y = v;
             }
         }
         "fit_pt_z" => {
-            if let Some(fp) = spline.fit_points.first_mut() {
+            if let Some(fp) = spline.fit_points.get_mut(fit_index) {
                 fp.z = v;
             }
         }
-        "fit_tolerance" => spline.fit_tolerance = v,
-        "start_tan_x" => spline.begin_tangent.x = v,
-        "start_tan_y" => spline.begin_tangent.y = v,
-        "start_tan_z" => spline.begin_tangent.z = v,
-        "end_tan_x" => spline.end_tangent.x = v,
-        "end_tan_y" => spline.end_tangent.y = v,
-        "end_tan_z" => spline.end_tangent.z = v,
+        "fit_tolerance" if v >= 0.0 => spline.fit_tolerance = v,
+        "start_tan_x" | "start_tan_y" | "start_tan_z" => {
+            if !tangent_is_set(&spline.begin_tangent) {
+                spline.begin_tangent = effective_begin_tangent;
+            }
+            match field {
+                "start_tan_x" => spline.begin_tangent.x = v,
+                "start_tan_y" => spline.begin_tangent.y = v,
+                "start_tan_z" => spline.begin_tangent.z = v,
+                _ => {}
+            }
+        }
+        "end_tan_x" | "end_tan_y" | "end_tan_z" => {
+            if !tangent_is_set(&spline.end_tangent) {
+                spline.end_tangent = effective_end_tangent;
+            }
+            match field {
+                "end_tan_x" => spline.end_tangent.x = v,
+                "end_tan_y" => spline.end_tangent.y = v,
+                "end_tan_z" => spline.end_tangent.z = v,
+                _ => {}
+            }
+        }
         _ => {}
     }
+    spline.flags.planar = is_planar(spline);
 }
 
 fn apply_grip(spline: &mut Spline, grip_id: usize, apply: GripApply) {
-    // Match the grip source: dragging a fit-point spline's grip moves the fit
-    // point (the curve re-fits through it on the next tessellation, keeping the
-    // stored end tangents); a CV spline moves the control vertex.
-    let target = if spline.control_points.is_empty() {
-        spline.fit_points.get_mut(grip_id)
-    } else {
+    if grip_id == SPLINE_MODE_GRIP_ID {
+        return;
+    }
+    // First CV edit makes the displayed kernel controls authoritative.
+    let fit_method = uses_fit_method(spline);
+    if spline.cv_frame_visible && fit_method {
+        if !convert_to_control_method(spline) {
+            return;
+        }
+    }
+    let target = if spline.cv_frame_visible || !fit_method {
         spline.control_points.get_mut(grip_id)
+    } else {
+        spline.fit_points.get_mut(grip_id)
     };
     if let Some(cp) = target {
         match apply {
@@ -614,96 +934,62 @@ impl crate::entities::traits::Grippable for Spline {
     fn apply_grip(&mut self, grip_id: usize, apply: GripApply) {
         apply_grip(self, grip_id, apply);
     }
-    fn grip_menu(&self, _grip_id: usize) -> Vec<crate::scene::model::object::GripMenuItem> {
+    fn grip_menu(&self, grip_id: usize) -> Vec<crate::scene::model::object::GripMenuItem> {
         use crate::scene::model::object::{GripMenuAction, GripMenuItem};
-        vec![
-            GripMenuItem {
-                label: "Stretch",
-                action: GripMenuAction::Stretch,
-            },
-            GripMenuItem {
-                label: "Add Vertex",
-                action: GripMenuAction::AddVertex,
-            },
-            GripMenuItem {
-                label: "Remove Vertex",
-                action: GripMenuAction::RemoveVertex,
-            },
-            GripMenuItem {
-                label: "Refine Vertices",
-                action: GripMenuAction::RefineVertices,
-            },
-        ]
+        if grip_id == SPLINE_MODE_GRIP_ID {
+            let fit_method = uses_fit_method(self);
+            let can_show_control = control_vertices(self).len() >= 2;
+            return if self.cv_frame_visible || !fit_method {
+                vec![
+                    (can_show_control && fit_method).then_some(GripMenuItem {
+                        label: "Fit",
+                        action: GripMenuAction::ShowFit,
+                    }),
+                    can_show_control.then_some(GripMenuItem {
+                        label: "✓ Control Vertices",
+                        action: GripMenuAction::ShowControlVertices,
+                    }),
+                ]
+                .into_iter()
+                .flatten()
+                .collect()
+            } else {
+                vec![
+                    Some(GripMenuItem {
+                        label: "✓ Fit",
+                        action: GripMenuAction::ShowFit,
+                    }),
+                    can_show_control.then_some(GripMenuItem {
+                        label: "Control Vertices",
+                        action: GripMenuAction::ShowControlVertices,
+                    }),
+                ]
+                .into_iter()
+                .flatten()
+                .collect()
+            };
+        }
+        vec![GripMenuItem {
+            label: "Stretch",
+            action: GripMenuAction::Stretch,
+        }]
     }
     fn apply_grip_menu(
         &mut self,
-        grip_id: usize,
+        _grip_id: usize,
         action: crate::scene::model::object::GripMenuAction,
     ) {
         use crate::scene::model::object::GripMenuAction as A;
-        let n = self.control_points.len();
-        let min_cv = (self.degree as usize).saturating_add(1).max(2);
         match action {
-            A::AddVertex if grip_id < n => {
-                let i1 = (grip_id + 1).min(n - 1);
-                if i1 == grip_id {
+            A::ShowFit => {
+                if convert_to_fit_method(self) {
+                    self.cv_frame_visible = false;
                     return;
                 }
-                let p0 = &self.control_points[grip_id];
-                let p1 = &self.control_points[i1];
-                let mid = acadrust::types::Vector3::new(
-                    (p0.x + p1.x) * 0.5,
-                    (p0.y + p1.y) * 0.5,
-                    (p0.z + p1.z) * 0.5,
-                );
-                self.control_points.insert(i1, mid);
-                if !self.weights.is_empty() && self.weights.len() == n {
-                    let w = (self.weights[grip_id] + self.weights[i1.min(self.weights.len() - 1)])
-                        * 0.5;
-                    self.weights.insert(i1, w);
-                }
-                // Clear knots so to_render rebuilds a uniform knot vector
-                // for the new CV count.
-                self.knots.clear();
             }
-            A::RemoveVertex if grip_id < n && n > min_cv => {
-                self.control_points.remove(grip_id);
-                if grip_id < self.weights.len() {
-                    self.weights.remove(grip_id);
-                }
-                self.knots.clear();
-            }
-            A::RefineVertices => {
-                // Insert a CV between every adjacent pair (chord midpoints)
-                // and rebuild a uniform knot vector.
-                if n >= 2 {
-                    let mut refined = Vec::with_capacity(n * 2 - 1);
-                    let mut refined_w = Vec::with_capacity(n * 2 - 1);
-                    let has_w = !self.weights.is_empty() && self.weights.len() == n;
-                    for i in 0..n {
-                        refined.push(self.control_points[i].clone());
-                        if has_w {
-                            refined_w.push(self.weights[i]);
-                        }
-                        if i + 1 < n {
-                            let a = &self.control_points[i];
-                            let b = &self.control_points[i + 1];
-                            refined.push(acadrust::types::Vector3::new(
-                                (a.x + b.x) * 0.5,
-                                (a.y + b.y) * 0.5,
-                                (a.z + b.z) * 0.5,
-                            ));
-                            if has_w {
-                                refined_w.push((self.weights[i] + self.weights[i + 1]) * 0.5);
-                            }
-                        }
-                    }
-                    self.control_points = refined;
-                    if has_w {
-                        self.weights = refined_w;
-                    }
-                    self.knots.clear();
-                }
+            A::ShowControlVertices if control_vertices(self).len() >= 2 => {
+                self.cv_frame_visible = true;
+                return;
             }
             _ => {}
         }

src/locale_catalog.rs

@@ -577,6 +577,7 @@ pub(super) fn message_attribute(source: &str) -> Option<(&'static str, &'static
         "Character Spacing" => Some(("properties", "character-spacing")),
         "Check your internet or proxy connection, then retry. Manually added repositories remain available." => Some(("plugins", "check-your-internet-or-proxy-connection-then-r")),
         "Choose New to capture the current layer settings." => Some(("layers", "choose-new-to-capture-the-current-layer-settin")),
+        "Chord" => Some(("properties", "chord")),
         "Chord X" => Some(("properties", "chord-x")),
         "Chord Y" => Some(("properties", "chord-y")),
         "Chord Z" => Some(("properties", "chord-z")),
@@ -645,6 +646,10 @@ pub(super) fn message_attribute(source: &str) -> Option<(&'static str, &'static
         "Control Point X" => Some(("properties", "control-point-x")),
         "Control Point Y" => Some(("properties", "control-point-y")),
         "Control Point Z" => Some(("properties", "control-point-z")),
+        "Control Vertices" => Some(("properties", "control-vertices")),
+        "Control point X" => Some(("properties", "control-point-x-sentence-case")),
+        "Control point Y" => Some(("properties", "control-point-y-sentence-case")),
+        "Control point Z" => Some(("properties", "control-point-z-sentence-case")),
         "Coordinates" => Some(("common", "coordinates")),
         "Coordination Model" => Some(("properties", "coordination-model")),
         "Copied path: {}" => Some(("common", "copied-path")),
@@ -666,6 +671,9 @@ pub(super) fn message_attribute(source: &str) -> Option<(&'static str, &'static
         "Current Color Scheme" => Some(("properties", "current-color-scheme")),
         "Current MLeader style: {}" => Some(("layers", "current-mleader-style")),
         "Current Vertex" => Some(("properties", "current-vertex-title-case")),
+        "Current Control point" => Some(("properties", "current-control-point")),
+        "Current Fit point" => Some(("properties", "current-fit-point")),
+        "CV frame" => Some(("properties", "cv-frame")),
         "Current annotation scale: {name}" => Some(("view", "current-annotation-scale-name")),
         "Current dim style set to '{}'." => Some(("common", "current-dim-style-set-to")),
         "Current layer" => Some(("layers", "current-layer")),
@@ -961,6 +969,9 @@ pub(super) fn message_attribute(source: &str) -> Option<(&'static str, &'static
         "End Tangent X" => Some(("properties", "end-tangent-x")),
         "End Tangent Y" => Some(("properties", "end-tangent-y")),
         "End Tangent Z" => Some(("properties", "end-tangent-z")),
+        "End tangent vector X" => Some(("properties", "end-tangent-vector-x")),
+        "End tangent vector Y" => Some(("properties", "end-tangent-vector-y")),
+        "End tangent vector Z" => Some(("properties", "end-tangent-vector-z")),
         "End X" => Some(("properties", "end-x")),
         "End Y" => Some(("properties", "end-y")),
         "End Z" => Some(("properties", "end-z")),
@@ -1066,6 +1077,10 @@ pub(super) fn message_attribute(source: &str) -> Option<(&'static str, &'static
         "Fit Point Y" => Some(("properties", "fit-point-y")),
         "Fit Point Z" => Some(("properties", "fit-point-z")),
         "Fit Tolerance" => Some(("properties", "fit-tolerance")),
+        "Fit point X" => Some(("properties", "fit-point-x-sentence-case")),
+        "Fit point Y" => Some(("properties", "fit-point-y-sentence-case")),
+        "Fit point Z" => Some(("properties", "fit-point-z-sentence-case")),
+        "Fit tolerance" => Some(("properties", "fit-tolerance-sentence-case")),
         "Fit to paper" => Some(("plot", "fit-to-paper")),
         "Fit/Smooth" => Some(("properties", "fit-smooth-title-case")),
         "Fit/smooth" => Some(("properties", "fit-smooth-sentence-case")),
@@ -1258,6 +1273,7 @@ pub(super) fn message_attribute(source: &str) -> Option<(&'static str, &'static
         "Kilometers" => Some(("common", "kilometers")),
         "Kind" => Some(("model", "kind")),
         "Knot Parameterization" => Some(("properties", "knot-parameterization")),
+        "Knot parameterization" => Some(("properties", "knot-parameterization-sentence-case")),
         "LANDXMLIMPORT  path to the .xml file:" => Some(("view", "landxmlimport-path-to-the-xml-file")),
         "LANDXMLIMPORT: cannot read \"{path}\": {e}" => Some(("view", "landxmlimport-cannot-read-path-e")),
         "LANDXMLIMPORT: imported {} survey point(s). Use ZOOM EXTENTS to view." => Some(("view", "landxmlimport-imported-survey-point-s-use-zoom")),
@@ -1701,6 +1717,8 @@ pub(super) fn message_attribute(source: &str) -> Option<(&'static str, &'static
         "Number of Grips" => Some(("properties", "number-of-grips")),
         "Number of Vertices" => Some(("properties", "number-of-vertices")),
         "Number of turns" => Some(("properties", "number-of-turns")),
+        "Number of control points" => Some(("properties", "number-of-control-points")),
+        "Number of fit points" => Some(("properties", "number-of-fit-points")),
         "OBJECTSCALE: added the active scale to {n} object(s)." => Some(("view", "objectscale-added-the-active-scale-to-n-object")),
         "OBJECTSCALE: select objects first." => Some(("view", "objectscale-select-objects-first")),
         "OBJECTSCALE: the active annotation scale is unavailable." => Some(("view", "objectscale-the-active-annotation-scale-is-una")),
@@ -1905,6 +1923,7 @@ pub(super) fn message_attribute(source: &str) -> Option<(&'static str, &'static
         "Pinned" => Some(("common", "pinned")),
         "Pitch And Family" => Some(("properties", "pitch-and-family")),
         "Place text manually (DIMUPT)" => Some(("common", "place-text-manually-dimupt")),
+        "Periodic" => Some(("properties", "periodic")),
         "Planar" => Some(("properties", "planar")),
         "Platform" => Some(("ui", "platform")),
         "Plot" => Some(("common", "plot")),
@@ -2192,6 +2211,7 @@ pub(super) fn message_attribute(source: &str) -> Option<(&'static str, &'static
         "SOLID  Specify second point:" => Some(("draw", "solid-specify-second-point")),
         "SOLID  Specify third point:" => Some(("draw", "solid-specify-third-point")),
         "SPLINE  Specify first control point:" => Some(("draw", "spline-specify-first-control-point")),
+        "SPLINE  Specify first point:" => Some(("draw", "spline-specify-first-point")),
         "SPLINE  Specify next point  [%{n} pts]:" => Some(("draw", "spline-specify-next-point-n-pts")),
         "SPLINEDIT  Select spline:" => Some(("modify", "splinedit-select-spline")),
         "SPLINEDIT  [CLOSE/OPEN/REVERSE/EXIT]:" => Some(("modify", "splinedit-close-open-reverse-exit")),
@@ -2323,6 +2343,7 @@ pub(super) fn message_attribute(source: &str) -> Option<(&'static str, &'static
         "Shortcut '{key}' not found." => Some(("view", "shortcut-key-not-found")),
         "Shortcut '{key}' removed." => Some(("view", "shortcut-key-removed")),
         "Shortcut set: {key} → {cmd_str}" => Some(("view", "shortcut-set-key-cmd-str")),
+        "Hide" => Some(("properties", "hide")),
         "Show" => Some(("properties", "show")),
         "Show Annotation Objects" => Some(("ui", "show-annotation-objects")),
         "Show Clipping" => Some(("properties", "show-clipping")),
@@ -2368,6 +2389,10 @@ pub(super) fn message_attribute(source: &str) -> Option<(&'static str, &'static
         "Start Tangent X" => Some(("properties", "start-tangent-x")),
         "Start Tangent Y" => Some(("properties", "start-tangent-y")),
         "Start Tangent Z" => Some(("properties", "start-tangent-z")),
+        "Start tangent vector X" => Some(("properties", "start-tangent-vector-x")),
+        "Start tangent vector Y" => Some(("properties", "start-tangent-vector-y")),
+        "Start tangent vector Z" => Some(("properties", "start-tangent-vector-z")),
+        "Square Root" => Some(("properties", "square-root")),
         "Start X" => Some(("properties", "start-x")),
         "Start Y" => Some(("properties", "start-y")),
         "Start Z" => Some(("properties", "start-z")),
@@ -2768,6 +2793,7 @@ pub(super) fn message_attribute(source: &str) -> Option<(&'static str, &'static
         "Usage: {prefix} NEW <name>" => Some(("layers", "usage-prefix-new-name")),
         "Usage: {prefix} OBLIQUE <style> <angle_degrees>" => Some(("layers", "usage-prefix-oblique-style-angle-degrees")),
         "Usage: {prefix} WIDTH <style> <factor>" => Some(("layers", "usage-prefix-width-style-factor")),
+        "Uniform" => Some(("properties", "uniform")),
         "Use Limits" => Some(("properties", "use-limits")),
         "Used for the first save of a new drawing. Existing drawings keep their file type and version." => Some(("file", "used-for-the-first-save-of-a-new-drawing-exist")),
         "User\nInterface" => Some(("manage", "user-interface")),

src/modules/draw/draw/spline.rs

@@ -1,7 +1,7 @@
 // Spline tool — ribbon definition + interactive command.
 //
 // Command:  SPLINE (SPL)
-//   Click to add control points.  Enter (≥2 pts) → commits EntityType::Spline.
+//   Click to add fit points. Enter (≥2 pts) → commits EntityType::Spline.
 
 use acadrust::types::Vector3;
 use acadrust::{EntityType, Spline};
@@ -11,7 +11,6 @@ use crate::command::{CadCommand, CmdResult};
 use crate::modules::{IconKind, ModuleEvent, ToolDef};
 use crate::scene::model::wire_model::WireModel;
 use glam::DVec3;
-use cadkernel::space::NurbsCurve3;
 
 #[allow(dead_code)]
 pub fn tool() -> ToolDef {
@@ -36,70 +35,43 @@ impl SplineCommand {
         if self.pts.len() < 2 {
             return None;
         }
-        let control_points = self
+        let fit_points = self
             .pts
             .iter()
             .map(|p| Vector3::new(p.x, p.y, p.z))
             .collect();
-        let n = self.pts.len();
-        // Uniform open knot vector for degree-3 clamped B-spline
-        let degree = 3_i32.min((n - 1) as i32);
-        let knots = uniform_knots(n, degree as usize);
         let mut spline = Spline {
-            degree,
-            control_points,
-            knots,
+            degree: 3,
+            fit_points,
             ..Default::default()
         };
-        // Closed splines render with a segment bridging the last point back to
-        // the first (tessellation honours `flags.closed`).
         spline.flags.closed = closed;
         Some(EntityType::Spline(spline))
     }
 }
 
-fn uniform_knots(n: usize, d: usize) -> Vec<f64> {
-    let m = n + d + 1;
-    (0..m)
-        .map(|i| {
-            if i <= d {
-                0.0
-            } else if i >= m - d - 1 {
-                1.0
-            } else {
-                (i - d) as f64 / (n - d) as f64
-            }
-        })
-        .collect()
-}
-
-/// Sample the degree-3 clamped B-spline through `pts` into a dense polyline,
-/// built with the same control points + knot vector `build()` commits so the
-/// preview traces the exact final curve — not the straight control polygon.
-/// Fewer than 2 points has no curve; the points are returned as-is.
-fn sample_curve(pts: &[DVec3]) -> Vec<[f32; 3]> {
-    let n = pts.len();
-    if n < 2 {
+/// Preview through the same fit-point representation that `build()` commits.
+fn sample_curve(pts: &[DVec3], closed: bool) -> Vec<[f32; 3]> {
+    if pts.len() < 2 {
         return pts
             .iter()
             .map(|p| [p.x as f32, p.y as f32, p.z as f32])
             .collect();
     }
-    let degree = 3_usize.min(n - 1);
-    let ctrl: Vec<[f64; 3]> = pts.iter().map(|p| [p.x, p.y, p.z]).collect();
-    let Some(curve) = NurbsCurve3::new(degree, ctrl, uniform_knots(n, degree), None) else {
-        return pts
+    let mut spline = Spline {
+        degree: 3,
+        fit_points: pts
             .iter()
-            .map(|p| [p.x as f32, p.y as f32, p.z as f32])
-            .collect();
+            .map(|p| Vector3::new(p.x, p.y, p.z))
+            .collect(),
+        ..Default::default()
     };
-    // Resolution scales with span count so long splines stay smooth.
-    let steps = 24 * (n - 1);
-    (0..=steps)
-        .map(|i| {
-            let p = curve.point_at(i as f64 / steps as f64);
-            [p[0] as f32, p[1] as f32, p[2] as f32]
-        })
+    spline.flags.closed = closed;
+    crate::entities::curve::spline_curve(&spline)
+        .map(|curve| crate::entities::curve::curve_points(&curve))
+        .unwrap_or_else(|| crate::entities::spline::measurement_polyline(&spline))
+        .into_iter()
+        .map(|p| [p[0] as f32, p[1] as f32, p[2] as f32])
         .collect()
 }
 
@@ -110,7 +82,7 @@ impl CadCommand for SplineCommand {
 
     fn prompt(&self) -> String {
         if self.pts.is_empty() {
-            t!("SPLINE  Specify first control point:").into_owned()
+            t!("SPLINE  Specify first point:").into_owned()
         } else {
             let n = self.pts.len();
             t!("SPLINE  Specify next point  [%{n} pts]:", n = n).into_owned()
@@ -135,9 +107,6 @@ impl CadCommand for SplineCommand {
     }
 
     fn on_enter(&mut self) -> CmdResult {
-        // A spline gathers many points into ONE entity, so finishing must end
-        // the command (CommitAndExit) — CommitEntity keeps the command armed
-        // with the accumulated points and traps the cursor in a redraw loop.
         match self.build(false) {
             Some(e) => CmdResult::CommitAndExit(e),
             None => CmdResult::Cancel,
@@ -156,7 +125,6 @@ impl CadCommand for SplineCommand {
     }
 
     fn wants_text_input(&self) -> bool {
-        // Accept Close / Undo once a control point exists.
         !self.pts.is_empty()
     }
 
@@ -182,14 +150,12 @@ impl CadCommand for SplineCommand {
         if self.pts.is_empty() {
             return None;
         }
-        // Preview the actual B-spline curve, treating the cursor as the next
-        // control point, sampled exactly like the committed entity — not the
-        // straight control polygon.
+        // Preview the committed fit-point representation.
         let mut ctrl = self.pts.clone();
         ctrl.push(pt);
         Some(WireModel::solid(
             "rubber_band".into(),
-            sample_curve(&ctrl),
+            sample_curve(&ctrl, false),
             WireModel::CYAN,
             false,
         ))

src/modules/draw/modify/spline_ops.rs

@@ -96,15 +96,18 @@ fn spline_to_nurbs_with(
         let flat = vector(v);
         (flat[0] * flat[0] + flat[1] * flat[1] > 1e-18).then_some(flat)
     };
+    let start_tangent = tangent(&spl.begin_tangent);
+    let end_tangent = tangent(&spl.end_tangent);
+    let parameterization = match spl.knot_parameterization {
+        2 => Parameterization::Uniform,
+        1 => Parameterization::Centripetal,
+        _ => Parameterization::Chord,
+    };
     NurbsCurve::interpolate(
         &fit,
-        tangent(&spl.begin_tangent),
-        tangent(&spl.end_tangent),
-        match spl.knot_parameterization {
-            2 => Parameterization::Uniform,
-            1 => Parameterization::Centripetal,
-            _ => Parameterization::Chord,
-        },
+        start_tangent,
+        end_tangent,
+        parameterization,
     )
 }
 

src/scene/model/object.rs

@@ -83,6 +83,8 @@ pub enum GripShape {
     Rectangle,
     Triangle,
     Circle,
+    /// Screen-offset menu selector.
+    Dropdown,
 }
 
 /// Describes one grip point for an entity.
@@ -163,6 +165,8 @@ pub enum GripMenuAction {
     RemoveFitPoint,
     Refit,
     RefineVertices,
+    ShowFit,
+    ShowControlVertices,
     MoveWithText,
     StackText,
     UnstackText,

src/scene/pick/grip.rs

@@ -10,6 +10,17 @@ use crate::scene::model::object::{GripDef, GripShape};
 pub const GRIP_THRESHOLD_PX: f32 = 8.0;
 /// Half-size of the rendered grip square / diamond in pixels.
 pub const GRIP_HALF_PX: f32 = 5.0;
+/// Screen offset for dropdown selectors anchored to a vertex.
+pub const GRIP_DROPDOWN_OFFSET_X_PX: f32 = 24.0;
+pub const GRIP_DROPDOWN_OFFSET_Y_PX: f32 = 27.0;
+
+fn marker_screen_position(mut point: Point, shape: GripShape) -> Point {
+    if shape == GripShape::Dropdown {
+        point.x += GRIP_DROPDOWN_OFFSET_X_PX;
+        point.y += GRIP_DROPDOWN_OFFSET_Y_PX;
+    }
+    point
+}
 
 // ── Active drag state ─────────────────────────────────────────────────────
 
@@ -106,6 +117,7 @@ pub fn grips_to_screen(
                     camera.project(g.world + dir, bounds)?,
                 ))
             });
+            let screen = marker_screen_position(screen, g.shape);
             (g.id, screen, g.is_midpoint, g.shape, dir)
         })
         .collect()
@@ -131,7 +143,7 @@ pub fn grips_to_screen_paper(
         .iter()
         .map(|g| {
             let projected = project(g.world);
-            let screen = Point::new(projected.x, projected.y);
+            let screen = marker_screen_position(Point::new(projected.x, projected.y), g.shape);
             let dir = g.dir.map(|dir| {
                 [
                     dir.x as f32 / (2.0 * half_w) * bounds.width,
@@ -157,9 +169,12 @@ pub fn find_hit_grip_paper(
     let mut best: Option<(usize, usize, bool, DVec3)> = None;
 
     for (index, g) in grips.iter().enumerate() {
-        let screen = Point::new(
-            (g.world.x as f32 - tx + half_w) / (2.0 * half_w) * bounds.width,
-            (ty + half_h - g.world.y as f32) / (2.0 * half_h) * bounds.height,
+        let screen = marker_screen_position(
+            Point::new(
+                (g.world.x as f32 - tx + half_w) / (2.0 * half_w) * bounds.width,
+                (ty + half_h - g.world.y as f32) / (2.0 * half_h) * bounds.height,
+            ),
+            g.shape,
         );
         let dx = screen.x - cursor.x;
         let dy = screen.y - cursor.y;
@@ -187,7 +202,7 @@ pub fn find_hit_grip(
         let Some(screen) = camera.project(g.world, bounds) else {
             continue;
         };
-        let screen = Point::new(screen.x, screen.y);
+        let screen = marker_screen_position(Point::new(screen.x, screen.y), g.shape);
         let dx = screen.x - cursor.x;
         let dy = screen.y - cursor.y;
         let d = (dx * dx + dy * dy).sqrt();
@@ -239,6 +254,7 @@ pub fn grips_to_screen_rte(
                     project_rte(g.world + dir, view_rot, eye, bounds)?,
                 ))
             });
+            let screen = marker_screen_position(screen, g.shape);
             (g.id, screen, g.is_midpoint, g.shape, dir)
         })
         .collect()
@@ -260,6 +276,7 @@ pub fn find_hit_grip_rte(
         let Some(screen) = project_rte(g.world, view_rot, eye, bounds) else {
             continue;
         };
+        let screen = marker_screen_position(Point::new(screen.x, screen.y), g.shape);
         let dx = screen.x - cursor.x;
         let dy = screen.y - cursor.y;
         let d = (dx * dx + dy * dy).sqrt();

src/ui/overlay.rs

@@ -261,6 +261,7 @@ pub fn selection_overlay<'a>(
     snap_ext_base: Option<Point>,
     snap_ext_base2: Option<Point>,
     grips: Vec<GripMarker>,
+    control_polygon: Option<(Vec<Point>, bool)>,
     grip_clip: Option<iced::Rectangle>,
     ucs_icons: Vec<UcsIconParams>,
     ost_points: Vec<OstTrackPoint>,
@@ -282,6 +283,7 @@ pub fn selection_overlay<'a>(
         snap_ext_base,
         snap_ext_base2,
         grips,
+        control_polygon,
         grip_clip,
         ucs_icons,
         ost_points,
@@ -312,6 +314,8 @@ struct SelectionCanvas {
     /// both crossing extensions stay drawn when the crossing is caught. (#247, #259)
     snap_ext_base2: Option<Point>,
     grips: Vec<GripMarker>,
+    /// Selected spline control polygon and closed state.
+    control_polygon: Option<(Vec<Point>, bool)>,
     /// Active 3D pane / floating viewport rectangle. Grip markers are clipped
     /// here so orbiting cannot leak them into paper space or adjacent panes.
     grip_clip: Option<iced::Rectangle>,
@@ -401,6 +405,12 @@ fn draw_grip_marker(frame: &mut canvas::Frame, grip: &GripMarker, theme: &Theme)
             b.close();
         }),
         GripShape::Circle => canvas::Path::circle(Point::new(sp.x, sp.y), h),
+        GripShape::Dropdown => canvas::Path::new(|b| {
+            b.move_to(Point::new(sp.x - h, sp.y - h * 0.5));
+            b.line_to(Point::new(sp.x + h, sp.y - h * 0.5));
+            b.line_to(Point::new(sp.x, sp.y + h));
+            b.close();
+        }),
     };
 
     if grip.is_hot {
@@ -419,10 +429,12 @@ fn draw_grip_marker(frame: &mut canvas::Frame, grip: &GripMarker, theme: &Theme)
     } else {
         let palette = theme.palette();
         let color = palette.primary.base.color;
-        frame.fill(
-            &path,
-            palette.background.base.color.scale_alpha(0.7),
-        );
+        let fill = if grip.shape == GripShape::Dropdown {
+            color
+        } else {
+            palette.background.base.color.scale_alpha(0.7)
+        };
+        frame.fill(&path, fill);
         frame.stroke(
             &path,
             canvas::Stroke {
@@ -695,6 +707,31 @@ impl canvas::Program<Message> for SelectionCanvas {
                 height: grip_y1 - grip_y0,
             };
             frame.with_clip(grip_clip, |frame| {
+                if let Some((points, closed)) = &self.control_polygon {
+                    if points.len() >= 2 {
+                        let polygon = canvas::Path::new(|builder| {
+                            builder.move_to(points[0]);
+                            for point in points.iter().skip(1) {
+                                builder.line_to(*point);
+                            }
+                            if *closed {
+                                builder.line_to(points[0]);
+                            }
+                        });
+                        frame.stroke(
+                            &polygon,
+                            canvas::Stroke {
+                                width: 1.0,
+                                style: canvas::Style::Solid(Color::from_rgb(0.72, 0.32, 0.15)),
+                                line_dash: canvas::LineDash {
+                                    segments: &[4.0, 4.0],
+                                    offset: 0,
+                                },
+                                ..Default::default()
+                            },
+                        );
+                    }
+                }
                 for grip in &self.grips {
                     draw_grip_marker(frame, grip, theme);
                 }