1 files changed, 173 insertions, 0 deletions
diff --git a/src/dynamics/joint/multibody_joint/multibody_link.rs b/src/dynamics/joint/multibody_joint/multibody_link.rs
new file mode 100644
index 0000000..94bd3de
--- /dev/null
+++ b/src/dynamics/joint/multibody_joint/multibody_link.rs
@@ -0,0 +1,173 @@
+use std::ops::{Deref, DerefMut};
+
+use crate::dynamics::{MultibodyJoint, RigidBodyHandle};
+use crate::math::{Isometry, Real};
+use crate::prelude::RigidBodyVelocity;
+
+pub(crate) struct KinematicState {
+    pub joint: MultibodyJoint,
+    pub parent_to_world: Isometry<Real>,
+    // TODO: should this be removed in favor of the rigid-body position?
+    pub local_to_world: Isometry<Real>,
+    pub local_to_parent: Isometry<Real>,
+}
+
+impl Clone for KinematicState {
+    fn clone(&self) -> Self {
+        Self {
+            joint: self.joint.clone(),
+            parent_to_world: self.parent_to_world.clone(),
+            local_to_world: self.local_to_world.clone(),
+            local_to_parent: self.local_to_parent.clone(),
+        }
+    }
+}
+
+/// One link of a multibody.
+pub struct MultibodyLink {
+    pub(crate) name: String,
+    // FIXME: make all those private.
+    pub(crate) internal_id: usize,
+    pub(crate) assembly_id: usize,
+    pub(crate) is_leaf: bool,
+
+    pub(crate) parent_internal_id: usize,
+    pub(crate) rigid_body: RigidBodyHandle,
+
+    /*
+     * Change at each time step.
+     */
+    pub(crate) state: KinematicState,
+
+    // FIXME: put this on a workspace buffer instead ?
+    pub(crate) velocity_dot_wrt_joint: RigidBodyVelocity,
+    pub(crate) velocity_wrt_joint: RigidBodyVelocity,
+}
+
+impl MultibodyLink {
+    /// Creates a new multibody link.
+    pub fn new(
+        rigid_body: RigidBodyHandle,
+        internal_id: usize,
+        assembly_id: usize,
+        parent_internal_id: usize,
+        joint: MultibodyJoint,
+        parent_to_world: Isometry<Real>,
+        local_to_world: Isometry<Real>,
+        local_to_parent: Isometry<Real>,
+    ) -> Self {
+        let is_leaf = true;
+        let velocity_dot_wrt_joint = RigidBodyVelocity::zero();
+        let velocity_wrt_joint = RigidBodyVelocity::zero();
+        let kinematic_state = KinematicState {
+            joint,
+            parent_to_world,
+            local_to_world,
+            local_to_parent,
+        };
+
+        MultibodyLink {
+            name: String::new(),
+            internal_id,
+            assembly_id,
+            is_leaf,
+            parent_internal_id,
+            state: kinematic_state,
+            velocity_dot_wrt_joint,
+            velocity_wrt_joint,
+            rigid_body,
+        }
+    }
+
+    pub fn joint(&self) -> &MultibodyJoint {
+        &self.state.joint
+    }
+
+    pub fn rigid_body_handle(&self) -> RigidBodyHandle {
+        self.rigid_body
+    }
+
+    /// Checks if this link is the root of the multibody.
+    #[inline]
+    pub fn is_root(&self) -> bool {
+        self.internal_id == 0
+    }
+
+    /// This link's name.
+    #[inline]
+    pub fn name(&self) -> &str {
+        &self.name
+    }
+
+    /// Sets this link's name.
+    #[inline]
+    pub fn set_name(&mut self, name: String) {
+        self.name = name
+    }
+
+    /// The handle of this multibody link.
+    #[inline]
+    pub fn link_id(&self) -> usize {
+        self.internal_id
+    }
+
+    /// The handle of the parent link.
+    #[inline]
+    pub fn parent_id(&self) -> Option<usize> {
+        if self.internal_id != 0 {
+            Some(self.parent_internal_id)
+        } else {
+            None
+        }
+    }
+
+    #[inline]
+    pub fn local_to_world(&self) -> &Isometry<Real> {
+        &self.state.local_to_world
+    }
+
+    #[inline]
+    pub fn local_to_parent(&self) -> &Isometry<Real> {
+        &self.state.local_to_parent
+    }
+}
+
+// FIXME: keep this even if we already have the Index2 traits?
+pub(crate) struct MultibodyLinkVec(pub Vec<MultibodyLink>);
+
+impl MultibodyLinkVec {
+    #[inline]
+    pub fn get_mut_with_parent(&mut self, i: usize) -> (&mut MultibodyLink, &MultibodyLink) {
+        let parent_id = self[i].parent_internal_id;
+
+        assert!(
+            parent_id != i,
+            "Internal error: circular rigid body dependency."
+        );
+        assert!(parent_id < self.len(), "Invalid parent index.");
+
+        unsafe {
+            let rb = &mut *(self.get_unchecked_mut(i) as *mut _);
+            let parent_rb = &*(self.get_unchecked(parent_id) as *const _);
+            (rb, parent_rb)
+        }
+    }
+}
+
+impl Deref for MultibodyLinkVec {
+    type Target = Vec<MultibodyLink>;
+
+    #[inline]
+    fn deref(&self) -> &Vec<MultibodyLink> {
+        let MultibodyLinkVec(ref me) = *self;
+        me
+    }
+}
+
+impl DerefMut for MultibodyLinkVec {
+    #[inline]
+    fn deref_mut(&mut self) -> &mut Vec<MultibodyLink> {
+        let MultibodyLinkVec(ref mut me) = *self;
+        me
+    }
+}