Scroll up and down line by line (from buffer) in c

I write code to extract data from xmltv listings and display them perchannel in page with 15 line. How to make to scroll up and down line by line in page (from buffer) until last line information from listings perchannel is end and them move to next page that display information for another channel?
channel 1:

Code:

|   line1   |                      |   line2   |                |-----------|
|   line2   |                      |   line3   |                |-----------|
|   line3   | scroll down line =>  |   line4   | then clear =>  | lastline  | 
|   line4   |                      |-----------|                |           |
|-----------|                      |   line15  |                |           |
|   line15  |                      |   line16  |                |           |

then move to => channel 2:

Code:

|   line1   |                      |   line2   |                |-----------|
|   line2   |                      |   line3   |                |-----------|
|   line3   | scroll down line =>  |   line4   | then clear =>  | lastline  |
|   line4   |                      |-----------|                |           |
|-----------|                      |   line15  |                |           |
|   line15  |                      |   line16  |                |           |

etc.

---

My code:

Code:

int epg_show_perchannel( tvtime_osd_t* osd, int page, station_mgr_t *stationmgr, xmltv_t *xmltv, int channel )
{
if (!page)
    return 0;
if ( xmltv ){
    const int buf_length = 255;
    const int max_num_lines = 15;
    const int num_stations = station_get_num_stations( stationmgr );
    char *old_channel = strdup( xmltv_get_channel( xmltv ) );
    char buf[buf_length+1];
    int cur = 0;
    time_t curtime = time( 0 );
    const char *xmltv_id = 0;

    if (channel > num_stations)  
        channel = 1;
    else if (channel < 1 )
        channel = num_stations;

    if (!(xmltv_id = station_get_xmltv_id( stationmgr, channel-1 ))) 
        xmltv_id = xmltv_lookup_channel( xmltv, station_get_name( stationmgr, channel-1 ));
    xmltv_set_channel( xmltv, xmltv_id);
    xmltv_refresh_withtime( xmltv, curtime );

    /* List header with Channel number + name */
    snprintf(buf, buf_length, "%d Next on [%s] %s:", channel, station_get_channel(stationmgr,channel-1), station_get_name( stationmgr, channel-1));
    tvtime_osd_list_set_text( osd, cur++, buf );
    tvtime_osd_list_set_hilight(osd, -1);   

    while ((cur-1) < max_num_lines) {
        xmltv_refresh_withtime( xmltv, curtime );

        if (xmltv_get_title( xmltv )) {
            char start_time[50];
            time_t start_timestamp = xmltv_get_start_time( xmltv );
            time_t end_timestamp = xmltv_get_end_time( xmltv );
            strftime( start_time, 50, "%H:%M", localtime( &start_timestamp ) );

            /* starttime of current program + Now showing program */
            snprintf(buf, buf_length, "%s %s", start_time, xmltv_get_title( xmltv ));       
            if (xmltv_get_sub_title( xmltv )){
                strncat(buf," (",buf_length-strlen(buf));  
                strncat(buf,xmltv_get_sub_title( xmltv ),buf_length-strlen(buf));
                strncat(buf,")",buf_length-strlen(buf));  
            }
            tvtime_osd_list_set_multitext( osd, cur++, buf, 1);

            if (!xmltv_get_next_title( xmltv )) {
                char end_time[50];
                /* no next program, print endtime of current programme */       
                strftime( end_time, 50, "%H:%M", localtime( &end_timestamp ) );
                snprintf(buf, buf_length, "%s %s", end_time, "");       
                tvtime_osd_list_set_multitext( osd, cur++, buf, 1);
            }
        curtime = end_timestamp;

        } else {
            /* No XMLTV information for this channel */
            tvtime_osd_list_set_text( osd, cur++, "");
        }

    }
    tvtime_osd_list_set_lines( osd, cur );
    tvtime_osd_show_list( osd, 1, 1 );

    xmltv_set_channel(xmltv, old_channel);
    free(old_channel);
    xmltv_refresh( xmltv );

} else {
    tvtime_osd_list_set_text( osd, 0, "No XMLTV Program Guide information available" );
    tvtime_osd_list_set_lines( osd, 1 );
    tvtime_osd_show_list( osd, 1, 1 );
}
return channel;
}

My code, actualy show page with only 15 line and then move to next channel.

I want to scroll down list until information from xmltv listings for channel is end, and then move to next channel.

Remarkably similar to > [git:tvtime/master] program guide from #1097855, needs some fixes, just cmnd-F and "your" code is almost verbatim there.