# Constraints on Redrawn Area (/main-modules/display/redraw_area)



Some display controllers have specific requirements for the window area where the
rendered image can be sent (e.g., `x1` must be even, and `x2` must be odd).

In the case of monochrome displays, `x1` must be `Nx8`, and `x2` must be `Nx8 - 1`.
(If the display uses `LV_COLOR_FORMAT_I1`, LVGL automatically applies this rounding.
See [Monochrome Displays](/main-modules/display/color_format).)

The size of the invalidated (redrawn) area can be controlled as follows:

```c title=" " lineNumbers=1
void rounder_event_cb(lv_event_t * e)
{
    lv_area_t * a = lv_event_get_invalidated_area(e);

    a->x1 = a->x1 & (~0x1); /* Ensure x1 is even */
    a->x2 = a->x2 | 0x1;    /* Ensure x2 is odd */
}

...

lv_display_add_event_cb(disp, rounder_event_cb, LV_EVENT_INVALIDATE_AREA, NULL);
```

API [#api]