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+Network Working Group                                           S. Crocker
+Request for Comments #86                                        January 5, 1971
+NIC 5631                                                        UCLA
+
+                 Proposal for a Network Standard Format
+             for a Data Stream to Control Graphics Display
+
+
+A typical arrangement of facilities is to have a console attached to a
+
+computer at the user's site, and to be using the computational facilities
+
+of a remote site.  Information entered by the user is transmitted to the
+
+remote Host, and output from the remote Host is transmitted back to the
+
+local user.  In this proposal I am concerned with specifying the form of
+
+the output stream for the case that the output portion of the console is a
+
+typical refresh display with point, vector and character drawing capability.
+
+Devices in this class include the DEC 338, DEC 340, IBM 2250, and IMLAC
+
+PDS-1.
+
+
+
+It must be understood that this proposal is illustrative only, and knowingly
+
+avoids important issues.  Its main purpose is to provide a basis for dis-
+
+cussion and development.
+
+
+
+In order to specify the semantices of the network standard graphics data
+
+stream (NGDS), I will postulate
+
+   1.   a network standard display list (NGDL)
+
+   2.   a network standard stream interpreter (NGSI)
+
+   3.   a network standard list interpreter (NGLI), also called the
+        display controller, and
+
+   4.   a network standard screen (NGS)
+
+
+
+                                                                [Page 1]
+
+The NGDS is accepted into the local Host and interpreted by the NGSI.  The
+
+NGSI is a process which modifies the NGDL according to inputs in the NGDS.
+
+The NGDL is the display list for the NGLI; the NGLI executes the NGDL and
+
+controls the beam which writes on the NGS.
+
+
+
+The NGS is square, has horizontal and vertical sides, and positions on it
+
+are specified by an ordered pair of unsigned 16 bit fractions.  The first
+
+fraction specifies the horizontal distance from the left hand edge, and
+
+the second specifies the vertical distance from the bottom edge.  The
+
+resolution of the screen is unspecified.
+
+
+
+The lack of specification of the resolution of the NGS is intentional;
+
+programs designers should not interpret this to mean that they may impose
+
+a particular requirement on the using system.  Thus the quality of the
+
+displayed picture should degrade gradually with decreasing resolution.
+
+
+
+The NGLI has primitives for moving the beam to a particular point, intensify-
+
+ing a point, drawing a vector, or drawing a character.  Characters are
+
+assumed to be not more than .015 screen width wide, and not more than .025
+
+screen height high.  When the beam is moved to a screen position before
+
+drawing characters, that position should be at the lower left hand corner
+
+of the first character drawn.  The beam position after drawing a character
+
+is immediately to the right of the character, properly positioned for another
+
+character.  However, after drawing one or more characters, the exact horizontal
+
+
+
+
+                                                                [Page 2]
+
+position of the beam is unspecified.
+
+
+
+The imprecise specification of character size is intended to take cognizance
+
+of the existance of character drawing hardware which is capable of producing
+
+only one or a few character sizes.  The particular proportions of .015 wide
+
+by .025 high provides for 67 characters to a line and 40 lines, and seems
+
+well within the capability of most displays in the class considered.  As in
+
+the case of screen resolution, variations in character drawing hardware
+
+should cause only minor degradation in the usefulness of the picture.
+
+
+
+The character set intrepreted by the NGLI is ASCII, excepting all form
+
+control characters, but including the space character.  The tab, return
+
+and line feed functions should be simulated by explicit positioning of the
+
+beam.
+
+
+
+The NGDL consists of a set of named and possibly null lists.  The names
+
+are 16 bit integers, and the name zero is the name of the chief list.
+
+Each list is composed of zero of more display items.  An item is any of
+
+the following:
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+                                                                [Page 3]
+
+a)  "Move beam to xxxx,yyyy, relative to current origin"
+
+   b)  "Display vector from current position to xxxx,yyyy, relative to
+        current origin"
+
+   c)  "Display current point"
+
+   d)  "Display the following n characters:
+
+       c  c  ...c "
+        1  2     n
+
+   e)  "Execute list gggg with origin xxxx,yyyy relative to current origin"
+
+
+
+The NGLI is constantly in a loop executing the chief list, the origin of
+
+the chief list is always <0,0>.  When the NGLI comes to the end of the
+
+chief list, it returns to the top of it.  When the NGLI encounters a
+
+type e item, it suspends execution of the current list, set the new origin
+
+to <xxxx,yyyy> + <the old origin>, and executes the list named gggg. When
+
+finished with the list, the old origin is restored and execution of the
+
+old list resumed.  The NGLI is, therefore, a recursive interpreter, and
+
+type e items are subroutine calls.
+
+
+
+There remains only the matter of the NGDS and the NGSI.  The NGDS is parsed
+
+into commands by the NGSI and each command is executed as soon as it is
+
+recognized.  The commands in the NGDS are in prefix form, consisting of an
+
+eight bit operation code followed by any arguments.  Only two commands
+
+are defined: Erase and Replace.
+
+
+The Erase command consists of a single zero-valued opcode and no arguments.
+
+The NGSI executes the Erase command by making all lists into null lists.
+
+
+
+                                                                [Page 4]
+
+This erases the screen.
+
+
+
+The Replace command has an opcode of 1, followed by a 16-bit list name,
+
+followed by an 8 bit subargument count, followed by the indicated number
+
+of subarguments.  The NGSI executes the Replcae command by deleteing all
+
+items from the indicated list, and rebuilding the list from the subarguments.
+
+There are five kinds of subarguments, corresponding to the five item types.
+
+
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+                                                                [Page 5]
+
+<subargument>::=<atype> | <btype> |  <ctype> |
+
+                                      <dtype> | <etype>
+
+
+            <atype>::= <a> <x> <y>
+
+            <btype>::= <b> <x> <y>
+
+            <ctype>::= <c>
+
+            <dtype>::= <d> <n> <c> ... <c>
+                                    n
+
+            <etype>::= <e> <g> <x> <y>
+
+
+
+<a>, <b>, <c>, <d>, and <e> are 8 bit bytes valued at 0, 1 ... 4,
+
+respectively and corresponging to the item types listed on page 4.
+
+
+            <x> and <y> are 16 bit numbers
+
+            <g> is a 16 bit list name
+
+            <n> is an 8 bit count
+
+            <c> is an ASCII character code
+
+
+
+       [ This RFC was put into machine readable form for entry ]
+         [ into the online RFC archives by Anand Kumria 6/97 ]
+
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+                                                                [Page 6]
+