/************************************************************************/
/* Fill 'display buffer' with text then display it                      */
/* in a split screen.  Use cursor keys to scroll the top half           */
/************************************************************************/

demo_split_screen()
        {
        #define KEY_ESC         0x011B
        #define KEY_UP          0x4800
        #define KEY_DOWN        0x5000
        #define KEY_LEFT        0x4B00
        #define KEY_RIGHT       0x4D00
        #define KEY_ENTER       0x1C0D
        #define MONO            5
        #define VMONO           7

        static  char    digits[] = {"0123456789"};
        static  char    text[]   = {"This is line 000"};
        int             i, line, key, size, port;

        /*--- Fill display buffer with text  ---                        */
        /* (cannot use printf since we want to go below line 25)        */

        for (i = 0; i < 400; i++)
                {
                text[15] = digits[i % 10];      /* Add line number      */
                text[14] = digits[(i/10)%10];
                text[13] = digits[(i/100)%10];
                write_string(i, 0, text);       /* Draw next text line  */
                }

        /*--- Smoothly move in the split line ---                       */

        size = get_scanlines()/2;               /* Last split to do     */
        for (i = get_scanlines(); i > size; i--)/* Loop over scanline   */
                split_screen(i);                /* to smoothly move in  */

        /*--- Use cursor keys to control the scroll ---                 */
        /* Each line of text takes 80 bytes, so to scroll down one      */
        /* line, we set START ADDRESS register in CRTC to 80 more       */

        line = 0;                               /* Initialize line pos  */
                                                /* Set CRTC address     */
        if (get_display_type() == MONO || get_display_type() == VMONO)
                port = 0x3B4;
        else
                port = 0x3D4;

        while((key = get_key()) != KEY_ENTER)
                {
                switch (key)
                        {
                        case KEY_UP:            /* Scroll up one line   */
                            line = (line > 0) ? --line : 0;
                            break;
                        case KEY_DOWN:          /* Scroll down one line */
                            line++;
                            break;
                        default:
                             break;
                        }
                write_register(port,0x0D);      /* Select CRTC START LO */
                write_register(port+1, line * 80);      /* Write low    */
                write_register(port,0x0C);      /* Select CRTC START HI */
                write_register(port+1,(line * 80)>>8);  /* Write high   */
                }

        /* Reset CRT START ADDRESS to 0 (no scroll)                     */

        write_register(port,0x0D);              /* Select CRTC START LO */
        write_register(port+1,0);               /* Write low            */
        write_register(port,0x0C);              /* Select CRTC START HI */
        write_register(port+1,0);               /* Write high           */

        /* Remove the split                                             */

        size = get_scanlines();                 /* Last split to do     */
        for (i = get_scanlines()/2; i <= size; i++)     /* Loop over    */
                split_screen(i);                /* to smoothly move out */
        }