Match Fix geometric constraint behavior

1) FXCONSTRAINT (and the new GCFIX name) prompts "Select point or [Object]
   <Object>:" — a pick fixes that constraint point; Enter or O asks for one
   line, polyline segment, circle, arc, ellipse or spline; misses and
   unsupported objects report the reference messages and re-prompt.
2) Point, block, text, MText, attribute and table insertion points are
   addressable constraint points.
3) Re-applying Fixed to the same point or object reports that the constraint
   already exists instead of adding a duplicate.
4) A persistent Fixed holds its pre-edit geometry through MOVE, ROTATE,
   SCALE, STRETCH, grip and Properties edits: fixed points stay, free points
   of a partly fixed entity follow the edit, and size retention skips fixed
   entities.
5) Object mode on a polyline fixes the picked segment (natively persisted)
   instead of the whole polyline; arc segments pin endpoints, center and
   radius.
6) Ribbon label "Fix" with a padlock icon.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

src/modules/parametric/fixed.rs

@@ -0,0 +1,139 @@
+//! GCFIX / FXCONSTRAINT — locks a constraint point, or a whole curve /
+//! polyline segment, at its current position. Picks resolve on the host (a
+//! `CadCommand` has no document access): `AddFixedConstraint` carries the
+//! click, the driver maps it to a `ParametricRef` and re-prompts on a miss,
+//! the way the reference does.
+
+use acadrust::{EntityType, Handle};
+use glam::DVec3;
+
+use crate::command::{CadCommand, CmdOption, CmdResult, CoincidentPick};
+use crate::scene::parametric_constraints::ParametricRef;
+
+#[derive(Clone, Copy)]
+enum Step {
+    PointOrObject,
+    Object,
+}
+
+pub struct FixConstraintCommand {
+    step: Step,
+}
+
+impl FixConstraintCommand {
+    pub const INVALID_OBJECT: &'static str =
+        "Invalid selection for Fixed. Select a line, polyline segment, circle, arc, ellipse or spline.";
+    pub const NO_POINT: &'static str = "No valid constraint point found.";
+    pub const NO_OBJECT: &'static str = "No object found.";
+
+    pub fn new() -> Self {
+        Self {
+            step: Step::PointOrObject,
+        }
+    }
+
+    /// The Object-mode reading of a single preselected entity: a whole
+    /// curve, or a one-segment polyline's segment. Anything else prompts.
+    pub fn preselected_reference(entity: &EntityType, handle: Handle) -> Option<ParametricRef> {
+        match entity {
+            EntityType::Line(_)
+            | EntityType::Circle(_)
+            | EntityType::Arc(_)
+            | EntityType::Ellipse(_)
+            | EntityType::Spline(_) => Some(ParametricRef::whole(handle)),
+            EntityType::LwPolyline(polyline) => (polyline.vertices.len() == 2
+                && !polyline.is_closed)
+                .then(|| ParametricRef::segment(handle, 0)),
+            EntityType::Polyline2D(polyline) => (polyline.vertices.len() == 2
+                && !polyline.is_closed())
+            .then(|| ParametricRef::segment(handle, 0)),
+            _ => None,
+        }
+    }
+
+    fn pick(&self, handle: Option<Handle>, point: DVec3) -> CmdResult {
+        CmdResult::AddFixedConstraint(CoincidentPick {
+            handle,
+            point,
+            whole_curve: matches!(self.step, Step::Object),
+        })
+    }
+}
+
+impl CadCommand for FixConstraintCommand {
+    fn name(&self) -> &'static str {
+        "FXCONSTRAINT"
+    }
+
+    fn prompt(&self) -> String {
+        match self.step {
+            Step::PointOrObject => "FXCONSTRAINT  Select point or [Object] <Object>:".to_string(),
+            Step::Object => "FXCONSTRAINT  Select object:".to_string(),
+        }
+    }
+
+    fn options(&self) -> Vec<CmdOption> {
+        matches!(self.step, Step::PointOrObject)
+            .then(|| vec![CmdOption::new("Object", "O")])
+            .unwrap_or_default()
+    }
+
+    fn wants_text_input(&self) -> bool {
+        true
+    }
+
+    fn point_step_accepts_keywords(&self) -> bool {
+        matches!(self.step, Step::PointOrObject)
+    }
+
+    fn on_text_input(&mut self, text: &str) -> Option<CmdResult> {
+        let keyword = text.trim().trim_start_matches('_').to_ascii_uppercase();
+        let to_object =
+            matches!(self.step, Step::PointOrObject) && matches!(keyword.as_str(), "O" | "OBJECT");
+        to_object.then(|| {
+            self.step = Step::Object;
+            CmdResult::NeedPoint
+        })
+    }
+
+    fn needs_entity_pick(&self) -> bool {
+        true
+    }
+
+    fn entity_pick_accepts_points(&self) -> bool {
+        true
+    }
+
+    fn entity_pick_highlights_hover(&self) -> bool {
+        true
+    }
+
+    fn on_entity_pick(&mut self, handle: Handle, point: DVec3) -> CmdResult {
+        if handle.is_null() {
+            return self.on_point(point);
+        }
+        self.pick(Some(handle), point)
+    }
+
+    fn on_point(&mut self, point: DVec3) -> CmdResult {
+        match self.step {
+            Step::PointOrObject => self.pick(None, point),
+            // A click on nothing at "Select object:".
+            Step::Object => CmdResult::ReportError(Self::NO_OBJECT.to_string()),
+        }
+    }
+
+    fn on_enter(&mut self) -> CmdResult {
+        match self.step {
+            Step::PointOrObject => {
+                self.step = Step::Object;
+                CmdResult::NeedPoint
+            }
+            Step::Object => CmdResult::Cancel,
+        }
+    }
+
+    fn on_escape(&mut self) -> CmdResult {
+        CmdResult::Cancel
+    }
+}

src/modules/parametric/mod.rs

@@ -6,6 +6,8 @@ mod coincident;
 mod concentric;
 mod constraint_bar;
 mod equal_distance;
+#[path = "fixed.rs"]
+mod fixed_command;
 mod geom_constraint;
 #[path = "horizontal.rs"]
 mod horizontal_command;
@@ -21,6 +23,7 @@ pub use coincident::{coincident_tool, CoincidentConstraintCommand};
 pub use concentric::ConcentricConstraintCommand;
 pub use constraint_bar::ConstraintBarOptionCommand;
 pub use equal_distance::{equal_distance_tool, EqualDistanceConstraintCommand};
+pub use fixed_command::FixConstraintCommand;
 pub use geom_constraint::GeomConstraintCommand;
 pub use horizontal_command::HorizontalConstraintCommand;
 pub use perpendicular_command::{PerpendicularConstraintCommand, PerpendicularPick};

src/modules/parametric/tools.rs

@@ -136,7 +136,7 @@ pub mod fixed {
     pub fn tool() -> ToolDef {
         ToolDef {
             id: "FXCONSTRAINT",
-            label: "Fixed",
+            label: "Fix",
             icon: IconKind::Svg(include_bytes!("../../../assets/icons/constrain/fixed.svg")),
             event: ModuleEvent::Command("FXCONSTRAINT".to_string()),
         }
@@ -171,6 +171,7 @@ inventory::submit!(crate::command::CommandRegistration {
         "NRCONSTRAINT",
         "LCONSTRAINT",
         "FXCONSTRAINT",
+        "GCFIX",
         "SYCONSTRAINT",
     ]
 });