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RFC 191 Charles Irby NIC 7136 Augmentation Research Center Category D.6, I.1 Stanford Research Institute



This document is a brief description of the way in which graphics terminals are conceptualized and used at the Augmentation Research Center. All things described are implemented and have been operational for several months. Although our attention has initially been centered about the display of textual material, we are now about to turn our attention toward pictorial displays (hopefully much enhanced over our previous 940 line drawing capabilities).

 This document will discuss only those facits of display use
 which have been implemented and are currently operational,
 namely only those dealing with textual display.

included is a discussion of the use of multiple file viewing display areas in NLS to provide cross file editing capabilities. A description of our display and terminal input equipment will be issued as a separate document.

NOTE: RFC 190 includes a functional description of the implementation of the interface to our displays and is a description of the way this interface was extended to include "Processor-displays" (an IMLAC PDS-1, in this case) to our system, thus enabling one to use Display NLS over any of our teletype lines (including the network).

 A "processor dsplay" is a display with Processing power which
 can be controlled by character strings.

Description of the "conceptual display" implemented at ARC

The allocatable output unit for our display terminals (which include our local terminals and all remote processor-displays) is

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a rectangular "display area". A program treats this display area much like it would a file which it has opened with write access.

When requesting the allocation of a display area, a program specifies its attributes, including where it is to be on the screen. The program is returned an identifier which it subsequently uses to manipulate images within the display area and the display area itself. Each string which the program writes into the display area is also given an identifier, which can subsequently be used to move, delete, replace, or change the characteristics of that string.

 The currently implemented characteristics are character size,
 horizontal spacing between characters, and font of the
 characters (e.g. blinking, italics, intensity, etc.).
 The position of items in the display area are given relative
 to the 0,0, which is the lower left corner of the display
 area.  The horizontal coordinate increases to the right and the
 vertical coordinate increases toward the top.

In addition to above described manipulation of strings within display areas a program can suppress the display of individual strings within display areas or suppress whole display areas.

Also, a program can switch the terminal's state from teletype simulation to display mode and vis versa.

 When in display mode, the teletype simulation display area is
 suppressed and the coordinates of the cursor are input with
 each character. When in teletype simulation mode, all user
 owned display areas are suppressed and the coordinates of the
 cursor are not input with each character.

At TENEX startup time, display areas are allocated for a teletype simulation and a cursor for each local display terminal. Programs can change the string being displayed as the cursor to give the human feedback as to the programs state.

Within NLS:

 The NLS subsystem deals only with the cursor and the display
 areas it has requested from the system for output to the user.
 The display area formatters assumes that the display has 64K
 by 64K addressable points (with 0,0 at upper left), several
 different character sizes and fonts, and 7-bit ASCII.
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 The display area formatters use format parameters during the
 format process and post-processors to convert the vertual
 format to one that is acceptable to the device for which the
 formatting was being done (a display area on the screen, a
 page for a printer, a microfilm device, or a teletype).
 NLS allows the user to specify arguments to commands by
 selecting items from the current display image. This is
 accomplished through the use of a data structure, which
 describes the current display image, to map the cursor
 coordinates, which are input with each character, into the
 proper selection.

Multiple text display areas in NLS

When the user's device is a display, NLS allows him to subdivide the file-viewing display area (the one in which he views his file) and view (and edit across) several different files at once. Following is a discussion of the commands and capabilities associated with this new feature.

new commands
  Horizontal split
    splits a file-viewing display area horizontally (into an
    upper and lower segment) at the selected location moving
    the image of the original display area to the upper or
    lower segment depending on whether the cursor is above or
    below the bugged position when the final Command Accept is
       No display area will be created which is smaller then 2
       lines by 20 columns (using the character size of the
       original display area).
  Vertical split
    splits a file-viewing display area vertically (into a left
    and right segment) at the selected location moving the
    image of the original display area to the left or right
    segment depending on whether the cursor is to the left or
    right of the selected position when the final CA is input.
       No display area will he created which is smaller then 2
       lines by 20 columns (using the character size of the
       original display area).
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  Move boundary
    The selected boundary is moved to the new position. A
    boundary will not be moved passed a boundary of a neighbor.
    A boundary is moved for all display areas for which it is a
    boundary. Any resulting display area which is smaller than
    two lines by twenty columns will be deleted.
  Character size
    The current character size of the display area which
    currently contains the cursor is displayed, and the user
    may type a number (0, 1, 2, 3) for a new character size.
    The final Command Accept causes the character size to be
    changed. The horizontal and vertical increment are
    automatically adjusted. Different display areas may
    simultaneously have different character sizes.
  Clear display area
    The selected display area is cleared, i.e. the image is
    erased, the return and file return rings are released, and
    the association of a file with that display area is
    removed. The display area itself is not deleted.

One may freely edit and jump using several display areas. The position of the cursor is used to resolve ambiguities.

 For example, If one executes a Jump command, the position of
 the cursor when the final Command Accept is entered determines
 in which display area the new image is to appear.
 Also, If one changes viewspecs using the leftmost two buttons
 of the mouse, the viewspecs of the display area containing the
 cursor when the buttons go down are used as the initial values
 and are displayed in the viewspec area. When the buttons are
 released, the display area containing the cursor receives the
 new viewspecs.
     [ This RFC was put into machine readable form for entry ]
     [ into the online RFC archives by BBN Corp. under the   ]
     [ direction of Alex McKenzie.                   12/96   ]
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/data/webs/external/dokuwiki/data/pages/rfc/rfc191.txt · Last modified: 1997/03/13 15:48 (external edit)