Expose revolute joints with separate local axes (#372)

* Expose revolute joints with separate local axes

* Update src/dynamics/joint.rs

Co-authored-by: Sébastien Crozet <sebastien@crozet.re>

---------

Co-authored-by: Sébastien Crozet <sebastien@crozet.re>

Author: zdtango

src.ts/dynamics/impulse_joint.ts

@@ -369,6 +369,10 @@ export class JointData {
     anchor1: Vector;
     anchor2: Vector;
     axis: Vector;
+    // #if DIM3
+    axis1: Vector;
+    axis2: Vector;
+    // #endif
     frame1: Rotation;
     frame2: Rotation;
     jointType: JointType;
@@ -588,6 +592,36 @@ export class JointData {
         res.jointType = JointType.Revolute;
         return res;
     }
+
+    /**
+     * Create a new joint descriptor that builds Revolute joints with independent
+     * local axes for each attached rigid-body.
+     *
+     * This is useful when the same world-space hinge axis is represented by
+     * different local axes on the two bodies.
+     *
+     * @param anchor1 - Point where the joint is attached on the first rigid-body affected by this joint. Expressed in the
+     *                  local-space of the rigid-body.
+     * @param anchor2 - Point where the joint is attached on the second rigid-body affected by this joint. Expressed in the
+     *                  local-space of the rigid-body.
+     * @param axis1 - Axis of the joint, expressed in the local-space of the first rigid-body.
+     * @param axis2 - Axis of the joint, expressed in the local-space of the second rigid-body.
+     */
+    public static revoluteWithAxes(
+        anchor1: Vector,
+        anchor2: Vector,
+        axis1: Vector,
+        axis2: Vector,
+    ): JointData {
+        let res = new JointData();
+        res.anchor1 = anchor1;
+        res.anchor2 = anchor2;
+        res.axis = axis1;
+        res.axis1 = axis1;
+        res.axis2 = axis2;
+        res.jointType = JointType.Revolute;
+        return res;
+    }
     // #endif
 
     public intoRaw(): RawGenericJoint {
@@ -674,9 +708,22 @@ export class JointData {
                 result = RawGenericJoint.spherical(rawA1, rawA2);
                 break;
             case JointType.Revolute:
-                rawAx = VectorOps.intoRaw(this.axis);
-                result = RawGenericJoint.revolute(rawA1, rawA2, rawAx);
-                rawAx.free();
+                if (!!this.axis1 && !!this.axis2) {
+                    let rawAx1 = VectorOps.intoRaw(this.axis1);
+                    let rawAx2 = VectorOps.intoRaw(this.axis2);
+                    result = RawGenericJoint.revoluteWithAxes(
+                        rawA1,
+                        rawA2,
+                        rawAx1,
+                        rawAx2,
+                    );
+                    rawAx1.free();
+                    rawAx2.free();
+                } else {
+                    rawAx = VectorOps.intoRaw(this.axis);
+                    result = RawGenericJoint.revolute(rawA1, rawA2, rawAx);
+                    rawAx.free();
+                }
                 break;
             // #endif
         }

src/dynamics/joint.rs

@@ -311,4 +311,28 @@ impl RawGenericJoint {
                 .into(),
         ))
     }
+
+    /// Create a new joint descriptor that builds Revolute joints with
+    /// independent local axes for each attached rigid-body.
+    ///
+    /// This is equivalent to a revolute generic joint with all linear axes
+    /// locked and only angular X free, but it preserves the local hinge axis
+    /// on each body instead of assuming they are identical.
+    #[cfg(feature = "dim3")]
+    pub fn revoluteWithAxes(
+        anchor1: &RawVector,
+        anchor2: &RawVector,
+        axis1: &RawVector,
+        axis2: &RawVector,
+    ) -> Option<RawGenericJoint> {
+        let axis1 = Unit::try_new(axis1.0, 0.0)?;
+        let axis2 = Unit::try_new(axis2.0, 0.0)?;
+        let joint: GenericJoint = GenericJointBuilder::new(JointAxesMask::LOCKED_REVOLUTE_AXES)
+            .local_anchor1(anchor1.0.into())
+            .local_anchor2(anchor2.0.into())
+            .local_axis1(axis1)
+            .local_axis2(axis2)
+            .into();
+        Some(Self(joint))
+    }
 }