How to update the display? - c++

Question

Here is the problem: I am using X11 to track events and then draw on the screen. When the drawing is finished I want do clear all data about the screen, because even if I call XCloseDisplay the application screen behaves weirdly. When I press a key on a keyboard the screen updates and this overlay disappears (I pressed print screen btn). I want to know, how to get this result through code.
while (1)
{
XNextEvent(xdisplay, &xevent);
if (xevent.type == ButtonPress)
{
init_x = xevent.xmotion.x_root;
init_y = xevent.xmotion.y_root;
printf("drawing area: init_x = %d, init_y = %d\n", init_x, init_y);
isPressed = true;
}
else if (xevent.type == ButtonRelease)
{
fin_x = xevent.xmotion.x_root;
fin_y = xevent.xmotion.y_root;
cairo_set_source_surface(cr, surfaceTmp, 1, 1);
cairo_set_fill_rule(cr, CAIRO_FILL_RULE_EVEN_ODD); // The default is CAIRO_FILL_RULE_WINDING.
cairo_rectangle(cr, 0, 0, DisplayWidth(xdisplay, scr), DisplayHeight(xdisplay, scr)); // set rectangle
cairo_fill(cr);
XFlush(xdisplay);
XCloseDisplay(xdisplay);
printf("drawing limit: fin_x = %d, fin_y = %d\n", fin_x, fin_y);
break;
}
if (xevent.type == MotionNotify && isPressed == true)
{
int tmp_x = xevent.xmotion.x_root;
int tmp_y = xevent.xmotion.y_root;
cairo_set_source_rgba(cr, 0, 0, 0, 0.2);
cairo_rectangle(cr, prevInitX, prevInitY, prevFinX, prevFinY);
cairo_fill(cr);
cairo_set_source_surface(cr, surfaceTmp, 1, 1);
cairo_set_fill_rule(cr, CAIRO_FILL_RULE_EVEN_ODD); // The default is CAIRO_FILL_RULE_WINDING.
cairo_rectangle(cr, init_x, init_y, tmp_x - init_x, tmp_y - init_y); // set rectangle
cairo_fill(cr);
prevInitX = init_x;
prevInitY = init_y;
prevFinX = tmp_x - init_x;
prevFinY = tmp_y - init_y;
}
}