screen¶

the on-screen text console (glass TTY): off, on, or report
NAME
    screen - the on-screen text console (glass TTY): off, on, or report

SYNOPSIS
    screen off      stop mirroring the console onto the GL screen
    screen on       mirror again (clears the screen and homes the cursor first)
    screen          report the current state

DESCRIPTION
    With a GL card fitted, the BIOS CONOUT MIRRORS every console byte onto
    the GL screen as well as the serial port, so the ROM monitor, the OS
    and every program appear on the display -- the "glass TTY" of two-mode
    operation (see the two-mode design). The mirror is ON BY DEFAULT
    whenever a card is present: the monitor switches it on at wake
    (GCONEN=1) and blanks the screen, so the very first banner is already
    on the LCD. Serial always carries the same output, and input stays on
    serial. (Console text uses the card's built-in character generator, not
    /FONT.GL -- the monitor still installs /FONT.GL from the CF root for GL
    TEXT, the stroke font graphics programs draw with.)

    screen is the switch. `screen off` clears the GCONEN flag and the
    console goes back to serial only -- use it when you want a program's
    graphics left undisturbed by the prompt, or when a test needs a
    pristine framebuffer. `screen on` sets the flag and calls the GCLS
    BIOS to clear the screen and home the text cursor. With no argument
    screen reports on or off. The setting lasts for the session: `exit`
    back to the monitor re-runs its wake-up, which switches the mirror on
    again.

    A full-screen GL program still SUSPENDS the console while it draws
    (the GTSUSP flag) and quitting back to the shell resumes it. Resuming
    does NOT clear the screen: a program's last frame stays put and the
    prompt draws over it, so incremental drawing across commands -- `gl`
    chains, `tri ... k` scenes -- keeps working. When you want a clean
    console again, `screen on` gives you one.

    On a machine with no display, `screen on` is a no-op and prints
    "screen: no display fitted".

    The console is a hardware TEXT OVERLAY -- a character-generator plane
    the card composites over the GL bitmap at scanout. So it SCROLLS when
    it fills the bottom row (older lines roll up; no clear-and-home), and
    backspace ERASES the cell (no leftover glyph). Its text floats over
    whatever the bitmap holds and never touches it.

EXAMPLES
    screen off      keep the GL screen for graphics; console on serial only
    screen on       console back on the LCD, from a clean screen
    term            the Term app: an on-screen shell in the app frame

SEE ALSO
    term, finder, gfx