RFC 186 (rfc186) - Page 1 of 17

Network graphics loader

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Network Working Group                                        J. Michener
Request for Comments: 186                                            MCG
NIC: 7130                                                   12 July 1971


                       A Network Graphics Loader

MOTIVATION

   The facility described herein will permit remote users on the ARPA
   network to obtain graphics output from programs they write for the
   Evans and Sutherland Line Drawing System Model 1 (LDS-1) located at
   the DMCG computer.  Also, users at that computer can employ the
   facility to do graphics on their ARDS and IMLAC consoles.

   INTRODUCTION

   The Graphics Loader on the Project MAC Dynamic Modeling/Computer
   Graphics PDP-10 is for use with the E&S LDS-1 display.  Display
   programs can be shipped to it and executed repeatedly.  The output,
   which would normally be visible at the PDP-10 installation, is
   transmitted to the originating site in digital form.

   Corrections and alterations to display programs can be transmitted so
   that the bulk of the program need be sent only once.  Any data or
   parameters which vary may be sent whenever they change.

   The originating site may request to have any part of its program or
   data transmitted back to it from the Graphics Loader.  With this
   feature it is possible to debug a display program which is
   incorrectly modifying itself.

   In order to simplify the Graphics Loader, it is assumed that the
   display program should occupy a contiguous block of core starting at
   location 1000 octal (i.e., it has been assembled absolutely), that
   its first executable instruction is at the same place, and that, when
   one frame is complete, it jumps to location 777 octal.

   The E&S LDS-1 has the capability of writing into memory the
   coordinates of endpoints of the line segments which would be visible
   to a user sitting at the LDS-1 display device.  A register called the
   Writer Address Register (WAR) is used to indicate an area of memory
   to contain these coordinates.  Various submodes are available for
   output to memory, but for the submode of greatest interest, "Scaled
   Coordinates to Memory" mode, each "visible" line segment causes two
   words of coordinate data to be stored.  The contents of the WAR are
   incremented for each word stored.




Michener
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