Add mj_multiRayNormal for multi-ray casting with normal computation (not exposed in public header)

PiperOrigin-RevId: 847821078
Change-Id: I616441d3460406a92a10731d1a086af6163e96ad

src/engine/engine_ray.h

@@ -30,11 +30,18 @@ MJAPI void mju_multiRayPrepare(const mjModel* m, const mjData* d,
                                int* geom_eliminate);
 
 // intersect multiple rays emanating from a single source
-// similar semantics to mj_ray, but vec is an array of (nray x 3) directions.
+// similar semantics to mj_ray, but vec is (nray x 3) and dist is (nray).
 MJAPI void mj_multiRay(const mjModel* m, mjData* d, const mjtNum pnt[3], const mjtNum* vec,
                        const mjtByte* geomgroup, mjtByte flg_static, int bodyexclude,
                        int* geomid, mjtNum* dist, int nray, mjtNum cutoff);
 
+// intersect multiple rays, compute normals if given
+// similar semantics to mj_rayNormal, but vec, normal and dist are arrays.
+MJAPI void mj_multiRayNormal(const mjModel* m, mjData* d, const mjtNum pnt[3], const mjtNum* vec,
+                             const mjtByte* geomgroup, mjtByte flg_static, int bodyexclude,
+                             int* geomid, mjtNum* dist, mjtNum* normal, int nray, mjtNum cutoff);
+
+
 // intersect ray (pnt+x*vec, x>=0) with visible geoms, except geoms on bodyexclude
 //  return geomid and distance (x) to nearest surface, or -1 if no intersection
 //  geomgroup, flg_static are as in mjvOption; geomgroup==NULL skips group exclusion