Fix/Unfix on every sketch entity: points (Fix constraint) and lines, arcs, circles, ellipses, splines and conics (fixed curves hold their points and radius); ConstraintFix takes entities (fixes them all unless all are fixed); the toolbar button and the context menu act on the whole selection; fixed points never move when dragged or solved; projected geometry counts as fixed; fixed geometry is drawn green; sketch.inspect reports fixed

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AS5Tn3xieewUSg3uxrMVdL

crates/sketch/src/link.rs

@@ -407,7 +407,15 @@ impl Sketch {
                 }
             };
             let cid = self.fresh(prefix);
-            self.curves.push(Curve { id: cid, kind, construction: false, reversed: false, link: Some(id.to_string()), centerline: false });
+            self.curves.push(Curve {
+                id: cid,
+                kind,
+                construction: false,
+                reversed: false,
+                link: Some(id.to_string()),
+                centerline: false,
+                fixed: false,
+            });
         }
         for li in &lay.lone {
             point(self, *li)?;

crates/sketch/src/model.rs

@@ -140,6 +140,9 @@ pub struct Curve {
     /// an axis (revolve, diameter dimensions).
     #[serde(default, skip_serializing_if = "std::ops::Not::not")]
     pub centerline: bool,
+    /// Fixed (locked): its points and radius are constants for the solver.
+    #[serde(default, skip_serializing_if = "std::ops::Not::not")]
+    pub fixed: bool,
 }
 
 /// Geometric constraints and dimensions. Indices refer to `Sketch::points` (`p`, `q`) or
@@ -536,7 +539,15 @@ impl Sketch {
             return Err(SketchError::Invalid("line needs two distinct points".into()));
         }
         let id = self.curve_id(id, "l")?;
-        self.curves.push(Curve { id, kind: CurveKind::Line { a, b }, construction: false, reversed: false, link: None, centerline: false });
+        self.curves.push(Curve {
+            id,
+            kind: CurveKind::Line { a, b },
+            construction: false,
+            reversed: false,
+            link: None,
+            centerline: false,
+            fixed: false,
+        });
         Ok(self.curves.len() - 1)
     }
 
@@ -565,7 +576,15 @@ impl Sketch {
             Some(i) if i < self.points.len() => i,
             _ => self.own_point(&id, "center", center)?,
         };
-        self.curves.push(Curve { id, kind: CurveKind::Circle { c, r }, construction: false, reversed: false, link: None, centerline: false });
+        self.curves.push(Curve {
+            id,
+            kind: CurveKind::Circle { c, r },
+            construction: false,
+            reversed: false,
+            link: None,
+            centerline: false,
+            fixed: false,
+        });
         Ok(self.curves.len() - 1)
     }
 
@@ -591,7 +610,15 @@ impl Sketch {
             Some(i) if i < n && i != a => i,
             _ => self.own_point(&id, "end", p1)?,
         };
-        self.curves.push(Curve { id, kind: CurveKind::Arc { c, a, b }, construction: false, reversed: false, link: None, centerline: false });
+        self.curves.push(Curve {
+            id,
+            kind: CurveKind::Arc { c, a, b },
+            construction: false,
+            reversed: false,
+            link: None,
+            centerline: false,
+            fixed: false,
+        });
         Ok(self.curves.len() - 1)
     }
 
@@ -680,6 +707,40 @@ impl Sketch {
         Ok(())
     }
 
+    /// Is point `i` held in place: fixed, projected (linked), fixed by a Fix constraint or a
+    /// point of a fixed curve.
+    pub fn point_locked(&self, i: usize) -> bool {
+        self.points.get(i).is_some_and(|p| p.fixed || p.link.is_some())
+            || self.constraints.iter().any(|c| c.kind == ConstraintKind::Fix { p: i })
+            || self.curves.iter().any(|c| c.fixed && c.kind.uses(i))
+    }
+
+    /// [`Sketch::point_locked`] for every point at once.
+    pub fn locked_points(&self) -> Vec<bool> {
+        let mut out: Vec<bool> = self.points.iter().map(|p| p.fixed || p.link.is_some()).collect();
+        let mut set = |i: usize| {
+            if let Some(x) = out.get_mut(i) {
+                *x = true;
+            }
+        };
+        for c in &self.constraints {
+            if let ConstraintKind::Fix { p } = c.kind {
+                set(p);
+            }
+        }
+        for c in self.curves.iter().filter(|c| c.fixed) {
+            for p in c.kind.point_ids() {
+                set(p);
+            }
+        }
+        out
+    }
+
+    /// Is curve `c` held in place: fixed or projected (linked).
+    pub fn curve_locked(&self, c: usize) -> bool {
+        self.curves.get(c).is_some_and(|c| c.fixed || c.link.is_some())
+    }
+
     /// Radius of a circle or arc.
     pub fn radius(&self, ci: usize) -> Option<f64> {
         match self.curves.get(ci)?.kind {
@@ -834,7 +895,7 @@ impl Sketch {
             }
         };
         let id = self.curve_id(id, prefix)?;
-        self.curves.push(Curve { id, kind, construction: false, reversed: false, link: None, centerline: false });
+        self.curves.push(Curve { id, kind, construction: false, reversed: false, link: None, centerline: false, fixed: false });
         Ok(self.curves.len() - 1)
     }
 

crates/sketch/src/solver.rs

@@ -70,6 +70,13 @@ fn layout(sk: &Sketch) -> Layout {
             *f = true;
         }
     }
+    for c in sk.curves.iter().filter(|c| c.fixed) {
+        for p in c.kind.point_ids() {
+            if let Some(f) = fixed.get_mut(p) {
+                *f = true;
+            }
+        }
+    }
     let mut n = 0;
     let pvar = fixed
         .iter()
@@ -86,7 +93,7 @@ fn layout(sk: &Sketch) -> Layout {
         .curves
         .iter()
         .map(|c| match c.kind {
-            CurveKind::Circle { .. } | CurveKind::Ellipse { .. } if c.link.is_none() => {
+            CurveKind::Circle { .. } | CurveKind::Ellipse { .. } if c.link.is_none() && !c.fixed => {
                 n += 1;
                 Some(n - 1)
             }