/* Helper function for draw_buf_rotate_90_sqr. Given a list of four numbers, rotate the entire list to the left.  */
static void draw_buf_rotate4(lv_color_t *a, lv_color_t *b, lv_color_t *c, lv_color_t *d)
/* Helper function for draw_buf_rotate_90_sqr. Given a list of four numbers, rotate the entire list to the left.  */
static void draw_buf_rotate4(lv_color_t *a, lv_color_t *b, lv_color_t *c, lv_color_t *d)
{
    lv_color_t tmp;
    tmp = *a;
    *a = *b;
    *b = *c;
    *c = *d;
    *d = tmp;
}