nsvg__addPoint
nsvg__addPoint(p, x, y);
nsvg__addPoint(p, px + dx/3.0f, py + dy/3.0f);
nsvg__addPoint(p, x - dx/3.0f, y - dy/3.0f);
nsvg__addPoint(p, x, y);
nsvg__addPoint(p, cpx1, cpy1);
nsvg__addPoint(p, cpx2, cpy2);
nsvg__addPoint(p, x, y);