grid_expand_line
grid_expand_line(gd, py, gd->sx, bg);
grid_expand_line(gd, py, px + 1, 8);
grid_expand_line(gd, py, px + slen, 8);
grid_expand_line(gd, yy, px + ox, 8); /* default bg first */
grid_expand_line(gd, py, px + nx, 8);
grid_expand_line(gd, py, dx + nx, 8);