1 files changed, 42 insertions, 0 deletions
diff --git a/src/constraint/anchor.rs b/src/constraint/anchor.rs
new file mode 100644
index 0000000..3ef94ff
--- /dev/null
+++ b/src/constraint/anchor.rs
@@ -0,0 +1,42 @@
+use nalgebra::{DVector, RowDVector};
+
+use crate::particle_system::{ParticleSystem, Point, Scalar, N};
+
+use super::Constraint;
+
+pub struct AnchorConstraint {
+    pub particle_id: usize,
+    pub anchor: Point,
+
+    jacobian: RowDVector<Scalar>,
+}
+
+impl ParticleSystem {
+    pub fn add_anchor_constraint(&mut self, particle_id: usize) {
+        let anchor = self.particles[particle_id].position;
+        self.constraints.push(Box::new(AnchorConstraint {
+            particle_id,
+            anchor,
+            jacobian: RowDVector::zeros(self.particles.len() * N),
+        }));
+    }
+}
+
+impl Constraint for AnchorConstraint {
+    fn get_particles(&self) -> Vec<usize> {
+        vec![self.particle_id]
+    }
+
+    fn c(&self, q: &DVector<Scalar>) -> Scalar {
+        let position = q.fixed_rows(self.particle_id * N);
+        (position - self.anchor.coords).norm()
+    }
+
+    fn set_jacobian(&mut self, jacobian: RowDVector<Scalar>) {
+        self.jacobian = jacobian
+    }
+
+    fn jacobian_prev(&self) -> RowDVector<Scalar> {
+        self.jacobian.clone()
+    }
+}