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+RFC 191                                             Charles Irby
+NIC 7136                            Augmentation Research Center
+Category D.6, I.1                    Stanford Research Institute
+                                                       13-JUL-71
+
+          GRAPHICS IMPLEMENTATION AND CONCEPTUALIZATION AT ARC
+
+Overview:
+
+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
+
+
+
+
+
+
+
+
+
+
+                                                                [Page 1]
+
+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.
+
+
+
+
+
+                                                                [Page 2]
+
+   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
+      input.
+
+         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).
+
+
+
+                                                                [Page 3]
+
+    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   ]
+
+
+
+
+
+
+
+                                                                [Page 4]
+