Start experimenting with a generic joint implementation for joint drives.

src/dynamics/joint/generic_joint.rs

@@ -0,0 +1,46 @@
+use crate::math::{Isometry, Real, SpacialVector, SPATIAL_DIM};
+
+#[derive(Copy, Clone, Debug)]
+#[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
+/// A joint that prevents all relative movement between two bodies.
+///
+/// Given two frames of references, this joint aims to ensure these frame always coincide in world-space.
+pub struct GenericJoint {
+    /// The frame of reference for the first body affected by this joint, expressed in the local frame
+    /// of the first body.
+    pub local_anchor1: Isometry<Real>,
+    /// The frame of reference for the second body affected by this joint, expressed in the local frame
+    /// of the first body.
+    pub local_anchor2: Isometry<Real>,
+    /// The impulse applied to the first body affected by this joint.
+    ///
+    /// The impulse applied to the second body affected by this joint is given by `-impulse`.
+    /// This combines both linear and angular impulses:
+    /// - In 2D, `impulse.xy()` gives the linear impulse, and `impulse.z` the angular impulse.
+    /// - In 3D, `impulse.xyz()` gives the linear impulse, and `(impulse[3], impulse[4], impulse[5])` the angular impulse.
+    pub impulse: SpacialVector<Real>,
+
+    pub min_position: SpacialVector<Real>,
+    pub max_position: SpacialVector<Real>,
+    pub target_velocity: SpacialVector<Real>,
+    /// The maximum negative impulse the joint can apply on each DoF. Must be <= 0.0
+    pub max_negative_impulse: SpacialVector<Real>,
+    /// The maximum positive impulse the joint can apply on each DoF. Must be >= 0.0
+    pub max_positive_impulse: SpacialVector<Real>,
+}
+
+impl GenericJoint {
+    /// Creates a new fixed joint from the frames of reference of both bodies.
+    pub fn new(local_anchor1: Isometry<Real>, local_anchor2: Isometry<Real>) -> Self {
+        Self {
+            local_anchor1,
+            local_anchor2,
+            impulse: SpacialVector::zeros(),
+            min_position: SpacialVector::zeros(),
+            max_position: SpacialVector::zeros(),
+            target_velocity: SpacialVector::zeros(),
+            max_negative_impulse: SpacialVector::repeat(-Real::MAX),
+            max_positive_impulse: SpacialVector::repeat(Real::MAX),
+        }
+    }
+}

src/dynamics/joint/joint.rs

@@ -1,6 +1,8 @@
 #[cfg(feature = "dim3")]
 use crate::dynamics::RevoluteJoint;
-use crate::dynamics::{BallJoint, FixedJoint, JointHandle, PrismaticJoint, RigidBodyHandle};
+use crate::dynamics::{
+    BallJoint, FixedJoint, GenericJoint, JointHandle, PrismaticJoint, RigidBodyHandle,
+};
 
 #[derive(Copy, Clone)]
 #[cfg_attr(feature = "serde-serialize", derive(Serialize, Deserialize))]
@@ -17,6 +19,7 @@ pub enum JointParams {
     /// A revolute joint that removes all degrees of degrees of freedom between the affected
     /// bodies except for the translation along one axis.
     RevoluteJoint(RevoluteJoint),
+    GenericJoint(GenericJoint),
 }
 
 impl JointParams {
@@ -26,8 +29,9 @@ impl JointParams {
             JointParams::BallJoint(_) => 0,
             JointParams::FixedJoint(_) => 1,
             JointParams::PrismaticJoint(_) => 2,
+            JointParams::GenericJoint(_) => 3,
             #[cfg(feature = "dim3")]
-            JointParams::RevoluteJoint(_) => 3,
+            JointParams::RevoluteJoint(_) => 4,
         }
     }
 
@@ -49,6 +53,15 @@ impl JointParams {
         }
     }
 
+    /// Gets a reference to the underlying generic joint, if `self` is one.
+    pub fn as_generic_joint(&self) -> Option<&GenericJoint> {
+        if let JointParams::GenericJoint(j) = self {
+            Some(j)
+        } else {
+            None
+        }
+    }
+
     /// Gets a reference to the underlying prismatic joint, if `self` is one.
     pub fn as_prismatic_joint(&self) -> Option<&PrismaticJoint> {
         if let JointParams::PrismaticJoint(j) = self {
@@ -81,6 +94,12 @@ impl From<FixedJoint> for JointParams {
     }
 }
 
+impl From<GenericJoint> for JointParams {
+    fn from(j: GenericJoint) -> Self {
+        JointParams::GenericJoint(j)
+    }
+}
+
 #[cfg(feature = "dim3")]
 impl From<RevoluteJoint> for JointParams {
     fn from(j: RevoluteJoint) -> Self {

src/dynamics/joint/mod.rs

@@ -1,5 +1,6 @@
 pub use self::ball_joint::BallJoint;
 pub use self::fixed_joint::FixedJoint;
+pub use self::generic_joint::GenericJoint;
 pub use self::joint::{Joint, JointParams};
 pub(crate) use self::joint_set::{JointGraphEdge, JointIndex};
 pub use self::joint_set::{JointHandle, JointSet};
@@ -9,6 +10,7 @@ pub use self::revolute_joint::RevoluteJoint;
 
 mod ball_joint;
 mod fixed_joint;
+mod generic_joint;
 mod joint;
 mod joint_set;
 mod prismatic_joint;