ffi->tb_init(); $w = $test->ffi->tb_width(); $h = $test->ffi->tb_height(); // try to set a cell out of bounds $err = $test->ffi->tb_set_cell(-1, -1, 'x', 0, 0); $errmsg = $test->ffi->tb_strerror($err); $test->ffi->tb_printf(0, 0, 0, 0, "oob err=%d errmsg=%s", $err, $errmsg); $test->ffi->tb_present(); $test->screencap();