docs: function addJoin(join_type, v, coordCurr, normPrev, normNext, isBeginning, context) {
      var miterVec = createMiterVec(normPrev, normNext);
      var isClockwise = (normNext[0] * normPrev[1] - normNext[1] * normPrev[0] > 0);
  
      if (context.texcoord_index != null) {
          zero_v[1] = v;
          one_v[1] = v;
      }
  
      if (isClockwise){
          addVertex(coordCurr, miterVec, miterVec, 1, v, context, 1);
          addVertex(coordCurr, normPrev, miterVec, 0, v, context, -1);
  
          if (!isBeginning) {
              indexPairs(1, context);
          }
  
          addFan(coordCurr,
              // extrusion vector of first vertex
              Vector.neg(normPrev),
              // controls extrude distance of pivot vertex
              miterVec,
              // extrusion vector of last vertex
              Vector.neg(normNext),
              // line normal (unused here)
              miterVec,
              // uv coordinates
              zero_v, one_v, zero_v,
              false, (join_type === JOIN_TYPE.bevel), context
          );
  
          addVertex(coordCurr, miterVec, miterVec, 1, v, context, 1);
          addVertex(coordCurr, normNext, miterVec, 0, v, context, -1);
      } else {
          addVertex(coordCurr, normPrev, miterVec, 1, v, context, 1);
          addVertex(coordCurr, miterVec, miterVec, 0, v, context, -1);
  
          if (!isBeginning) {
              indexPairs(1, context);
          }
  
          addFan(coordCurr,
              // extrusion vector of first vertex
              normPrev,
              // extrusion vector of pivot vertex
              Vector.neg(miterVec),
              // extrusion vector of last vertex
              normNext,
              // line normal for offset
              miterVec,
              // uv coordinates
              one_v, zero_v, one_v,
              false, (join_type === JOIN_TYPE.bevel), context
          );
  
          addVertex(coordCurr, normNext, miterVec, 1, v, context, 1);
          addVertex(coordCurr, miterVec, miterVec, 0, v, context, -1);
      }
  }