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Network graphics loader (RFC0186)

IP.com Disclosure Number: IPCOM000007195D
Original Publication Date: 1971-Jul-12
Included in the Prior Art Database: 2002-Mar-05
Document File: 18 page(s) / 31K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

J.C. Michener: AUTHOR

Abstract

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.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 13% of the total text.

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                                                        [Page 1]

RFC 186                A Network Graphics Loader            12 July 1971

   For each execution of the display program, the Graphics Loader sets

   the proper output mode (suppressing output to the cathode ray tube at

   the DGSD machine), initializes the WAR before execution and saves the

   final value of the WAR after execution.  Thus it is easy for the

   Graphics Loader to transmit to the user only the "visible output" of

   the display program.

DESCRIPTION OF REQUESTS FROM THE REMOTE USER PROGRAM

   Request are in the form of 36 bit words.  The first word of a request

   is interpreted as two 18 bit fields.  The left half contains a number

   identifying which of six operations is being requested.  The right

   half is either a mode or is ignored, depending on the requested

   operation.  (If the left half is not a valid operation number, an

   error message is sent and the next word is considered to begin a new

   request.)

   Depending upon the operatio...