Terminal and screen model

An OpenDoors session may have two displays: the remote user's terminal and the local operator's OpenDoors screen. They are related, but they are not assumed to have the same dimensions.

High-level display functions maintain a virtual representation of the remote screen. Its size is established from od_control.user_screenwidth and od_control.user_screen_length, subject to the legacy local-screen minimum. The local display shows the portion which fits in its own output area. Content outside that local area remains available to remote screen operations such as od_gettext() and the extended save/restore functions.

Direct calls to the lower-level ODScrn interface affect the local display only. They do not modify the remote screen model. This prevents local status or operator output from leaking into data later returned or restored by the high-level screen APIs.

Display modes

Plain text output works for every connection. Functions which position the cursor, manipulate rectangular screen areas, draw windows, or scroll arbitrary regions require ANSI or AVATAR terminal support unless their individual page states otherwise. The current mode is reported through fields such as od_control.user_ansi, user_avatar, and user_rip.

Coordinates are one-based. Functions which accept a rectangle use inclusive left, top, right, and bottom edges.

Raw and interpreted output

od_disp_str() and od_printf() are the normal choices for text. od_disp_emu() interprets terminal escape sequences while updating the screen model. od_disp() sends an explicit byte count and can suppress local echo; raw output sent without local echo cannot reliably be reconstructed and is not added to the virtual screen.

The legacy od_save_screen() interface retains its fixed 80-column save format for source and binary compatibility. New code which needs the complete remote screen should obtain the required size with od_save_screen_size() and use od_save_screen_ex() and od_restore_screen_ex().