Expose function for determining if tendons should be drawn using a catenary.

PiperOrigin-RevId: 931170146
Change-Id: Ia3352a3e2bdc5e4df932e9d476e1e34200b62df1

src/engine/engine_vis_visualize.c

@@ -1083,21 +1083,7 @@ static void addSiteGeoms(const mjModel* m, mjData* d, const mjvOption* vopt,
 }
 
 
-static void addSpatialTendonGeoms(const mjModel* m, mjData* d, const mjvOption* vopt, int catmask,
-                                  mjvScene* scn) {
-  const int category = mjCAT_DYNAMIC;
-  if (!(category & catmask)) {
-    return;
-  }
-  if (!vopt->flags[mjVIS_TENDON]) {
-    return;
-  }
-
-  for (int i=0; i < m->ntendon; i++) {
-    if (!vopt->tendongroup[mjMAX(0, mjMIN(mjNGROUP-1, m->tendon_group[i]))]) {
-      continue;
-    }
-
+int mjv_isCatenary(const mjModel* m, const mjData* d, int i, mjtNum* length) {
   int has_stiffness = m->tendon_stiffness[i] ||
                       !mju_isZero(m->tendon_stiffnesspoly+mjNPOLY*i, mjNPOLY);
 
@@ -1138,6 +1124,38 @@ static void addSpatialTendonGeoms(const mjModel* m, mjData* d, const mjvOption*
     }
   }
 
+  if (draw_catenary) {
+    // length of the tendon
+    if (limitedconstraint) {
+      *length = m->tendon_range[2*i+1];
+    } else {
+      *length = m->tendon_lengthspring[2*i+1];
+    }
+  }
+
+  return draw_catenary;
+}
+
+
+
+static void addSpatialTendonGeoms(const mjModel* m, mjData* d, const mjvOption* vopt, int catmask,
+                                  mjvScene* scn) {
+  const int category = mjCAT_DYNAMIC;
+  if (!(category & catmask)) {
+    return;
+  }
+  if (!vopt->flags[mjVIS_TENDON]) {
+    return;
+  }
+
+  for (int i=0; i < m->ntendon; i++) {
+    if (!vopt->tendongroup[mjMAX(0, mjMIN(mjNGROUP-1, m->tendon_group[i]))]) {
+      continue;
+    }
+
+    mjtNum length;
+    int draw_catenary = mjv_isCatenary(m, d, i, &length);
+
     // conditions not met: draw straight lines
     if (!draw_catenary) {
       for (int j=d->ten_wrapadr[i]; j < d->ten_wrapadr[i]+d->ten_wrapnum[i]-1; j++) {
@@ -1213,14 +1231,6 @@ static void addSpatialTendonGeoms(const mjModel* m, mjData* d, const mjvOption*
       mju_copy3(x0, d->wrap_xpos + 3*d->ten_wrapadr[i]);
       mju_copy3(x1, d->wrap_xpos + 3*d->ten_wrapadr[i] + 3);
 
-      // length of the tendon
-      mjtNum length;
-      if (limitedconstraint) {
-        length = m->tendon_range[2*i+1];
-      } else {
-        length = m->tendon_lengthspring[2*i+1];
-      }
-
       // get number of points along catenary path (capped at 100)
       int ncatenary = mjMIN(m->vis.quality.numslices + 1, 100);
       mjtNum catenary[300];

src/engine/engine_vis_visualize.h

@@ -65,6 +65,10 @@ MJAPI void mjv_cameraFrame(mjtNum headpos[3], mjtNum forward[3], mjtNum up[3], m
 MJAPI void mjv_cameraFrustum(float zver[2], float zhor[2], float zclip[2],  const mjModel* m,
                              const mjvCamera* cam);
 
+// determines if tendon should be rendered as a catenary curve and, if so, computes its length
+MJAPI int mjv_isCatenary(const mjModel* m, const mjData* d, int i, mjtNum* length);
+
+// computes points along a catenary curve
 int mjv_catenary(const mjtNum x0[3], const mjtNum x1[3], const mjtNum gravity[3], mjtNum length,
                  mjtNum* catenary, int ncatenary);