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RFC 282 - Graphics meeting report


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Network Working Group                                    M. A. Padlipsky
Request for Comments: 282                                    Project MAC
NIC: 8164                                               December 8, 1971

                        GRAPHICS MEETING REPORT

   The second Network Graphics Group Meeting was convened at the
   Stanford Artificial Intelligence Lab at 6:00p.m. Sunday, November
   21st.  (Attendees are listed in the Appendix.)  Jim Michener served
   as chairman, and I either volunteered or was volunteered to serve as
   recording secretary, with Karl Kelly's assistance in keeping notes.

   An agenda was agreed upon for the meeting, covering three major
   topics: 1) reports on the experiments which had been set up at the
   July meeting,  2) prepared talks by attendees who had general points
   to raise about Network Graphics, and  3) specification of a "first-
   pass" graphics protocol.  Before the reports were given, some general
   discussion was held on two important topics: the "context" problem
   (just how, in the Network sense, are graphics connections
   established, and who is supposed to do what for whom), and what might
   be called the "console types" problem (should there be a separate
   protocol for inherently static storage tube type devices and one for
   inherently interactive refresh type devices which have their own
   processors, or can we come up with some sort of continuous -- or
   layered -- single protocol which covers both).  Both points were
   noted as being necessary to keep in mind for the protocol
   specification phase of the meeting, an apparent consensus emerged
   that a single protocol would be preferable, and the reports on
   experiments were turned to.

REPORTS ON EXPERIMENTS

   RAND - UCSB

   Eric Harslem of RAND and Ron Stoughton of UCSB reported on their
   experiment, which entailed use of the UCSB On-Line System (OLS) from
   RAND Videographics terminals.  As demonstrated by a videotape which
   was shown, the experiment was successful.  An RFC describing the
   simple protocol they used is forthcoming.  As noted in their
   discussion and in the RFC, the experimental protocol is not being
   proposed as a Network standard.  In addition to using OLS from RAND,
   a subsidiary experiment tested the sensitivity of the hook-up to
   variations in the size of the allocations (in the Host-to-Host
   Protocol sense) given at the RAND end.  It seemed clear from the
   videotape of the same pictures being drawn at various allocation
   levels that larger allocations allow for noticeably smoother

   "drawing" at maximum allocation, the picture essentially appeared all
   at once, whereas at minimum allocation, NCP-NCP overhead was
   sufficiently large that the picture appeared a portion at a time.

   SDC - DMCG

   An experiment intended to input tablet data collected at MIT Project
   MAC's Dynamic Modeling/Computer Graphics Group's PDP-10 to a
   character recognizer package at SDC was reported on by Jean Saylor of
   SDC and Jim Michener of DMCG.  Problems ranging from
   hardware/software difficulties at both ends (and in the middle) to
   time zone-induced system availability conflicts retarded the
   experiment's progress, although some transmission of data has been
   achieved.

   ILLINOIS MULTICS

   Also plagued with problems was the attempt to drive a console at U.
   of Ill. from the Multics Graphics System.  This experiment was
   reported on by Jack Bouknight (Illinois) and Ed Meyer (Multics).  An
   NCP bug at the Multics end and a machine switch at the Illinois end
   combined to prevent the carrying out of the experiment.

   DIGRESSION

   During his report, Bouknight expressed concern as to whether the
   Network as a whole is as yet sufficiently reliable to support
   graphics work.  As the ensuing discussion focused on the frequent
   unavailability of a host other than Multics, I feel that it is within
   my province to draw the curtain of anonymity over it without
   prejudice.  However, I feel that mention of the discussion need not
   be suppressed as well, in view of the fact that most of the attendees
   shared Jack's concern.  The apparent consensus, reached after
   considerable conversation, is that the present reliability level of
   the Network server hosts is not crippling to graphics work, but can
   be quite hampering.

   SEX - NIC

   Jon Postel (UCLA) and John Melvin (SRI) gave the last experiment
   report, on an attempt to make an IMLAC on the SEX system look like a
   local NLS console at the Network Information Center.  The experiment
   has not yet been performed, but UCLA has ordered the necessary
   equipment to modify their IMLAC.

PRESENTATIONS

   Most of the speakers who gave prepared talks responded favorably to
   my plea for abstracts, probably out of kindness, but perhaps out of
   fear of (threatened) garbling.  Authors' abstracts are in quotation
   marks in the following section.

   PLASMA PANEL DISPLAY - Dave Liddle

   "The Owens - Illinois DS-1 terminal will be available to Network
   users who request them through ARPA.  The display module is the OI
   512X512 line plasma panel; the processor is a 16 bit, 4K machine with
   modem; ASCII keyboard, and optional tape cassette.  Simple software
   (character and vector generators, etc.) will be provided.  If orders
   can be assembled by 1 January, deliveries will begin this summer."

    LANGUAGES FOR GRAPHICS ATTENTION HANDLING - Ira Cotton

   "Available languages for programming the processing of operator
   inputs to a computer graphic system were organized into functional
   classes and briefly surveyed.  Some of the problems associated with
   providing this facility in a multi-computer graphics system (such as
   the Network) were discussed, and a new approach was presented.  This
   system, implemented by Univac for one of its systems, employs an
   interpretively executed command language to direct attention-handling
   in the remote graphics controller.  The commands of the language were
   outlined, and some program fragments illustrated."

   "INTERACTIVE" GRAPHICS ISSUES - Ken Pogran

   "The purpose of this talk was to raise a number of significant issues
   we must face in the development of a Network protocol for
   _interactive_ graphics.  While the bulk of the work at this second
   graphics meeting dealt with a protocol for "static" or "storage-tube"
   graphics, it is appropriate that we begin to think about the problems
   we will encounter in the development of an interactive graphics
   protocol."

   "The issues raised included: 1) the nature of graphical interaction,
   2) various possible hardware/software configurations which might be
   employed, 3) computational capabilities required at the serve and
   user host sites, 4) the nature of a graphical data structure suited
   to a wide range of applications, and 5) the nature and treatment of
   graphic inputs for a generalized interactive graphics system."

   PROTOCOL FOR THE OLS EXPERIMENT - Ron Stoughton, Eric Harslem

   "A short presentation was given describing a graphics protocol used
   to interface the RAND Videographics System to the USCB On-Line
   System.  A video tape of alive demonstration of the experiment [had
   also been] presented.  An RFC describing the experiment and protocol
   in detail will be issued in the near future."

   CONNECTION CONSIDERATIONS - Andy Moorer [Abstracted by M.A.P.]

   The topic was started succinctly as "how this thing should work."  It
   was proposed to use the Telnet Protocol for simple graphics (i.e.,
   when device dependent codes are being transmitted), with the addition
   of Telnet control codes for Enter graphics Mode, Leave Graphics Mode,
   and Console Type being necessary.  For complex graphics (i.e., when
   an intermediate form is being transmitted) it was proposed that an
   additional socket pair be employed.

   CONNECTION TYPES - Jim Michener [Abstracted by M.A.P]

   There are at least three types of graphics devices which may be
   connected over the Network: "simple" (ARDS-like), "smart" (IMLAC-
   like), and "powerful" (E&S-like).  There are three kinds of
   processing involved: applications packages (A), graphics packages
   (G), and conversion to device-specific codes (C), potentially from an
   intermediate form such as the "Network Standard Graphics Stream"
   discussed in earlier RFC's.  There are also three places where each
   kind of processing may be performed: at the graphics device itself,
   at the local host (which may not be able to help if it's a TIP), and
   at a remote host (OR HOST).  This should lead neatly to some sort of
   3X3X3 matrix which depicts the sorts of connections we want to
   support, but I don't know how to draw it.

   The talk leaned heavily on blackboard pictures of specific
   connections, but for purposes of this report, I'll try to summarize
   the situation in words.  For all simple devices, C must be performed
   "elsewhere"; if the simple device is on the Net via a TIP, C
   apparently must be performed either at the remote host (RH1) where A
   and G are, or at some other remote host (RH2) (which offers, say, the
   Data Reconfiguration Service).  Further, negotiations for C may have
   to be performed by RH1 on the TIP's behalf.  Still more complications
   result from the possible desirability of including an additional
   application (A') and/or an additional graphics package (G') on RH2.
   If the simple device is on the Net via a full-fledged local host
   (LH), then A, G, and C can each potentially be performed at LH or RH1
   -- or RH2 for that matter ("ship it to an E&S for clipping").

   In the case of smart devices, C can potentially be performed at the
   device itself - - although the TIP may not be able to furnish the
   extra socket pair which one would want in order to handle such cases
   cleanly.  Finally, powerful devices can do G internally but we may
   well wish to do A and G over the Net.  (Again, how the TIP would
   handle such cases was not clear.)

   Jim had presented this discussion for the expressed purpose of
   getting attention focused on the "ends" of the protocol pipeline
   before the meeting became totally concerned with the contents of that
   pipeline.  We responded in the only possible manner:

CONNECTION PROTOCOL COMMITTEE

   A committee was designated to formulate a Graphics Connection
   Protocol, the protocol to play an analogous role to that of the
   Initial Connection Protocol with respect to the Telnet Protocol.
   There was a clearcut consensus that only device-specific codes should
   be transmitted over Telnet connections unless the committee uncovered
   overwhelmingly convincing arguments to the contrary.  The committee
   consists of Michener, Bouknight, Harslem, and me.  Will Crowther of
   BBN will be invited to join the committee to furnish TIP
   representation and expertise.

GRAPHICS RESOURCE DOCUMENTATION

   Before turning to the protocol specification, it should be pointed
   out that most attendees felt that Resource Notebook-like
   documentation on Graphics should be prepared.  Postel volunteered to
   coordinate this effort.  Hosts should have drafts submitted to him,
   and he will see to getting them published as new portion of the
   Resource Notebook.  Format considerations were not discussed, but
   assumedly the format should imitate that of the main Resource
   Notebook sections.  Call Jon if you have questions (213-825-2368).

THE PROTOCOL

   At the outset of the main protocol discussion, it was agreed that a
   committee would be established to resolve those issues on which a
   consensus could not be reached at the meeting, and to prepare a draft
   of the protocol for distribution to the NGG by year's end.  Members
   of the committee are Michener, Meyer, Kelly, Cotton, and Liddle.

ASSUMPTIONS

   The following assumptions were agreed upon:

      1.  There shall be a "virtual screen" and a Standard Graphics
      Stream.

      2.  The origin is in the center.

      3.  Coordinates are signed, 2's complement fractions (-.5 to
      +.499).

      4.  The Standrd Graphics Stream will consist of 8-bit bytes
      initially, coordinates are two bytes. ( A "set coordinate size"
      operator will be introduced if and when needed.)

      5.  Network ASCII will be used for text output, with default to
      upper case where necessary.  Control characters are, for the time
      being, site specific.

      6.  Where appropriate, operators shall have "absolute,"
      "relative," and "local" (to a subpicture) modes.

      7.  The protocol will be organized on a "levels of complexity"
      basis, with level 0 comprising operators for simple picture
      drawing, level 1 comprising operators for one level of subpicture
      definition ("macros", or loosely, "subroutines") and level 2
      comprising "viewport" and "window" type operators.

   Note that the discussion dealt specifically with graphics OUTPUT.
   The Protocol Committee was also empowered to prepare recommendations
   for an input-side protocol, but first priority is to be attached to
   the formulation of an acceptable output-side protocol.

   OPERATORS

   As the Protocol Committee's draft is not immediately available, the
   following list of low-level operators (the syntax and semantics of
   which were discussed at length during the meeting) may be of interest
   here:

      1. Erase and reset to origin.  This operator causes the screen to
      be erased and the beam to be positioned at the 0,0 (virtual screen
      center) point.  A new picture is started.

      2. Move.  No line is drawn the beam is positioned to the specified
      x, y position.  There are specific operators for "move relative",
      "move absolute" and "move local" modes.

      3. Draw.  A line (of the current "linetype" -- see 5, below) is
      drawn from the present beam position to the specified x, y
      position.  Modes are as with move.  Treatment of the "off-screen"
      condition is at the displaying host's option.

      4. Point.  Display a point at the specified position.  Modes are
      as with move.

      5. Line type.  Draw lines of the specified type until further
      notice.  Currently defined types are solid (0), dashed (1), dotted
      (2).  If a requested type is not implemented, default to the
      next-lower-valued type.  After an "erase", type is solid until
      changed.

      6. Line intensity.  Requests line intensity to be as follows: 0 =
      off, 128 = normal, 255 = brightest, intermediate values = map
      appropriately.  After an "erase", intensity is normal until
      changed.

      7. Text.  Cause display of a specified number of specified (Net
      ASCII) characters.  There are specific operators for "return beam"
      after last character (to position before text display) and "leave
      beam" (wherever it ends up).  Size is to be whatever the
      displaying host considers "normal".  Treatment of "right-hand
      margin" and ASCII controls is host-specified at present.  (A
      character size operator may be specified later.)

      8. Escape.  If the console is  of specified type, pass a specified
      number of bytes directly to it.

   Operators for viewports and subpictures were also discussed.
   Bouknight and Kelly prepared an BNF treatment of all points
   discussed, which will appear in the Protocol Committee's draft.

OTHER BUSINESS

   The remaining technical discussion dealt with graphic input, on a
   rather general level.

   Michener extended the attendees' thanks to Andy Moorer for having
   hosted the meeting.

   Cotton volunteered to host the next meeting at Mitre, Washington, in
   mid-April, at which time we hope to have had enough experience with
   the connection protocol and first-pass output protocol to agree on a
   "final" statement of them, and to have done enough thinking about the
   input side to specify a first-pass protocol for it (unless the
   Protocol Committee manages to do so first)

APPENDIX - LIST OF ATTENDEES

    Marshall Abrams, Ntl. Bureau of Stds.

    Jack Bouknight, U. of Ill.

    Jackson T. Cole, Rome Air Development Ctr.

    Ira Cotton, MITRE

    Daniel Debrosse, UTAH

    Eric Harslem, RAND

    Karl Kelly, U. of Ill.

    David Liddle, Owens Illinois

    John Melvin, SRI

    Ed Meyer, MAC

    James Michener, MAC

    James Moorer, SAIL

    Hamid Naficy, UCLA

    Mike Padlipsky, MAC

    Ken Pogran, MAC

    Jon Postel, UCLA

    Jerry Powell, MITRE

    Jean Saylor, SDC

    Ron Stoughton, UCSB

    Elaine Thomas, BBN

    Howard Wactlar, Carnegie-Mellon

    Bill White, SUHP

         [This RFC was put into machine readable form for entry]
     [into the online RFC archives by Kelly Tardif, Viagénie 10/99]

 

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