code: public void addTris (float[] xys, int xysOffset, int xysLen, float tw, float th,
                         int[] indices, int indicesOffset, int indicesLen, int indexBase) {
      int vertIdx = beginPrimitive(xysLen/2, indicesLen), offset = vertPos;
      float[] verts = vertices, stables = stableAttrs;
      for (int ii = xysOffset, ll = ii+xysLen; ii < ll; ii += 2) {
        float x = xys[ii], y = xys[ii+1];
        offset = add(verts, add(verts, offset, stables), x, y, x/tw, y/th);
      }
      vertPos = offset;
  
      addElems(vertIdx, indices, indicesOffset, indicesLen, indexBase);
    }
docs: Adds triangle primitives to a prepared batch. This must be preceded by calls to
  {@link #setTexture} and {@link #prepare} to configure the texture and stable attributes.