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Network Working Group                                         E. HarslemRequest for Comments: 94                                      J. HeafnerNIC: 5725                                                3 February 1971Some Thoughts on Network GraphicsPurpose   This note states some of our initial reactions to NWG/RFC #86, whose   purpose was to provide a basis for discussion and development of   Network graphics.   The method of operation described in Note 86 was to interpret data   structures to produce graphic order codes for display.  This method   has proven satisfactory in the past and we favor this approach.  The   Note 86 proposal is directed toward a particular concept of operation   (i.e., minimal graphics terminal connected to computational   facilities at remote sites); our remarks embrace extended operations   that include smart programs at each end of the connection as well as   the minimal terminal.   The proposal in Note 86 should be broadened to include the   description of more complex entities and it should be raised to a   level of describing more general things.  In this note, we first   criticize the limitations imposed by the details of Note 86; then   suggest some supplementary ingredients to extend its scope; and   lastly, we suggest an alternate approach that reduces Network   conversations (where possible) to symbol manipulation rather than   gross detail.Comments on the Detailed Restrictions of Note 86   The detailed constraints enumerated in Note 86 restrict many   interesting features of the Rand display hardware that we consider   necessary (from a human factors standpoint) to some current   applications.  They likewise restrict other nodes whose ARPA-   sponsored research is dependent upon the use of sophisticated   hardware.  For example, the point, vector, and character capability   of Note 86 excludes line type mode, intensity control, and many other   attractive control operations; the maximum symbol sizes are too small   for our large character size; the origin of all of our symbols is   specified as the "centroid" of the symbol rather than the lower left   corner of a virtual rectangle encompassing the symbol; under mode   control for plotting purposes, the beam may not be advanced to the   next character position; a 7-bit ASCII is insufficient; etc.  In   short, the five list items of Note 86 are not expressive enough; for   example, there is nothing to allow one to position and open a graphicHarslem, et. al.                                                [Page 1]

RFC 94             Some Thoughts on Network Graphics       February 1971   compare "window".  The problem was not treated of supplying   parameters identifying structure for match, etc. that are not actual   display commands.   Perhaps some necessary information gathering (i.e., the display   hardware descriptions and the characteristics of every node) is   preliminary to the generation of a detailed specification.  It is   important that, without delay, a mechanism be defined for gathering   and collating this information in such a way that it doesn't deter   progress on Network graphics development.Some General Extensions to the Note 86 Proposal   1. DISPLAY LANGUAGE CAPABILITIES SHOULD ENCOMPASS THE UNION OF      CURRENT AND ANTICIPATED NETWORK GRAPHICS HARDWARE.  Our experience      in exploring interactive graphics communication techniques for use      by researchers and non-programmers indicates that this is not just      a "motherhood".  The utility of such applications programs depends      highly upon incorporating sophisticated graphics hardware.  In      absence of those features, some programs simply won't be used.   2. THE DATA STRUCTURE SHOULD ALLOW LOGICAL AS WELL AS PICTORIAL      REPRESENTATION OF THE USER'S PROBLEM.  This close coupling of the      meaning of a picture with the actual picture is desirable from a      processing program's point of view, especially if a user is to      interact with the picture.  We have found this an efficient way to      operate with the GRAIL Project and its derivatives here at Rand.      This technique is included in a recently proposed graphics      language generated by Bob Anderson (Rand) and Ben Wegbreit      (Harvard).   3. TRANSMIT DEFINITIONS OF GRAPHICS AND THEN INSTANCES OF THEIR USE.      The attempt here is to raise the level of "conversation" between      programs (where possible) and to reduce processing overhead.  For      example, if one wishes to draw lots of resistors, why not      graphically define a resistor once and then transmit instances by      giving the definition name accompanied by attributes? A typical      form of an instance is shown below.         Item Name (position, size, intensity, scaling, labeling,                    rotation, etc.)      There are many examples of this approach such as the recent work      by William Newman (Utah) and many earlier studies at MIT.   4. PARTITION THE DISPLAY STRUCTURE FOR 1) STATIC VS. DYNAMIC      INFORMATION, AND 2) CONTEXT.  As opposed to refreshing an entire      picture whose domain is the entire screen, we have found it usefulHarslem, et. al.                                                [Page 2]

RFC 94             Some Thoughts on Network Graphics       February 1971      to give the processing routine (that wishes to draw a picture)      knowledge of only of a named rectangular portion of the CRT and an      accompanying display structure.  With our particular hardware we      can then update only the dynamic part of a picture rather than      regenerating the entire display structure.  Just as important, we      can logically assign areas of the CRT to different concurrent      processing routines.  Coupled with the logical/pictorial      representation noted in 2) above, this is a powerful technique.      Named partitions also naturally accommodate those applications      requiring multiple CRTs.   5. THE INTERPRETER COULD BE CONTEXT-DRIVEN THUS NOT RESTRICTING ITS      OUTPUT TO A SINGLE SET OF CRT ORDER CODES.  By providing cataloged      descriptions such as the "forms" discussed in Note #83, the      interpreter could reconfigure data destined for files, etc., as      well as a display.  The gain here in terms of adapting to a users'      Network needs is large; the price paid in terms of implementing      this increment of the interpreter is probably small.An Alternate Proposal   Note 86 mentions the case of a terminal at a node with a minimal HOST   connected to a remote computationally-oriented node.  The data   standard, which Note 86 suggests transmitting over the Network is   rather gross detail.  Also, the standard language is rather   inexpressive -- encompassing only a few simple notions.   An alternative approach is to consider the situation of communication   between non-minimal nodes (nodes with substantial memory and   computing power).  Here the Network standard data should be a high-   level macro form representing the instances of gross detail with the   power to deal with sophisticated graphics devices.  That is, the   standard language would be rich enough to express all the special   features of Network display devices.   This suggestion presents two problems.  First, how can a terminal   handle commands from a remote program of which its hardware is   incapable? The answer is that the remote program to which it is   connected is too sophisticated for the terminal -- the connection is   invalid.  A terminal should NORMALLY only connect to a program that   addresses no more than its hardware capabilities.  This concept   allows a standard under which a simple terminal and a simple program   can communicate (exactly the proposal of Note 86), yet a   sophisticated terminal can talk to a sophisticated program in a   high-level language, or it can talk to a simple program, all within   the same Network standard.Harslem, et. al.                                                [Page 3]

RFC 94             Some Thoughts on Network Graphics       February 1971   The second problem is that a minimal host might not have sufficient   facilities to translate from a powerful Network standard language   into the simple, detailed order codes of its terminals.   When required, the needs of a minimal site would be handled by   another Network node providing data reconfiguration services, AN   ESSENTIAL PART OF THIS PROPOSAL.  The reconfiguration would be done   on the basis of "forms" specifying translation form the Network   standard to the specific non-standard data format required by the   minimal node (i.e., tailored specifically to its hardware).  Whether   it would be graphic order codes or some intermediate form would   depend on the processing power and requirements of the minimal node.   Fig. 1 shows a schematic diagram of the key elements of such a   reconfiguration facility.  Fig. 2 shows the use of that facility by a   local display handler and its use as an intermediary by two remote   nodes requiring different degrees of external data reconfiguration.Harslem, et. al.                                                [Page 4]

RFC 94             Some Thoughts on Network Graphics       February 1971              Network                | ^                | |                | |                v |          +--------------+          | A Network    |     Local          | Process      |---> Files, Programs,          | Invoking the |<--- CRTs, etc.          | Interpreter  |          +--------------+                | ^                | |                | |                v |          +--------------+      +--------------+ (A user can access          |              |      |  User's      | the logical      |-->| Interpreter  |      |  Semantic    | representation of      |   |              |      |  Routines    | his problem.)      |   +--------------+      +--------------+      |             | ^           | ^      |             | |           | |      |             | |           | |      |             v |           v |      |           +-------------------+      |           |                   |      |           |   Primitive       |      |           |   Data Structure  |      |           |   Operators       |      |           |                   |      |           +-------------------+      |                           | ^      |                           | |   +--------------+               | |   | Data Base of |               v |   | "Forms" for  |         +------------------+   | Reconfigu-   |         |  Data Structure  |   | ration       |         |  Base:           |   +--------------+         |  1 - Pictorial   |                            |  2 - Logical     |                            +------------------+                   Fig. 1. Data Reconfiguration ServiceHarslem, et. al.                                                [Page 5]

RFC 94             Some Thoughts on Network Graphics       February 1971       Host Providing                        Host Providing   Computational Facility                Reconfiguration Service   +--------------------+  STANDARD  +-----------------------------+   |                    |   FORMAT   |  +----------+ +-----------+ |   |                    |------------|--|  Inter-  |-|  Display  | |   |                    | (of Macro  | /|  preter  | |  Handler  | |   |                    | Form Data) |//+----------+ +-----------+ |   +--------------------+            //--------------------|-------+                                    //                     |                                   /(                +-----------+                                  /  \               | Terminal  |                                 /    \              +-----------+                                /      \                               /        \                              /          \                   NON-STD.  /            \  NON-STD.     (Terminal Order Codes) /              \ (Detailed Data)                           /                \                          /                  \                         /                    \                        /                      \                       /                        \                      /                          \                     |                            |             +-------|-------+            +-------|-------+             |       |       |            | +-----------+ |     Minimum |       |       |            | |  Display  | | Minimum      Host   |       |       |            | |  Handler  | |  Host             |       |       |            | +-----------+ |             +-------|-------+            +-------|-------+                     |                            |               +-----------+                +-----------+               | Terminal  |                | Terminal  |               +-----------+                +-----------+                Fig. 2. Use of Data Reconfiguration Service         [ This RFC was put into machine readable form for entry ]             [ into the online RFC archives by Sergio Kleiman]Harslem, et. al.                                                [Page 6]