rfc553.txt

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         This primitive unit consists of a series of points, which will
         be displayed joined by lines in the best available manner.

         The intent is to use Flegal's algorithms to produce a smooth
         curve.

      Device-specific

         This primitive unit consists of any number of device specific
         commands.  The device type may be obtained through an
         interrogation command.

   Call units

      In addition to the name of the referenced subpicture, a call unit
      may include the following transformations:

         Master/instance rectangle: specifies a rectangle in the
         caller's space into which a specified rectangle of the callee's
         space is to be imaged.  This provides independent scaling in
         each coordinate as well as translation and clipping.

         Rotation.  It may be desirable to combine this with scaling
         using the familiar idea of homogeneous transformation.

         Intensity and color control.  In principle, a call could
         specify intensity increments (positive or negative) for each
         color.

         It is assumed that best effort will be used in scaling and
         rotation of text.  We recommend replacing it by a line when all
         else fails.





Irby, et. al.                                                   [Page 7]

RFC 553        Draft design for a text/graphics protocol    14 July 1973


   Initial state

      After the initial telnet connection is established, the first
      graphics command issued by the applications program should be a
      request for either a structured display file or for a segmented
      display file.

         The response to this request should be whether or not the
         requested display file was allocated and other parameters about
         the virtual display, e.g. screen size, character sizes, whether
         or not color is available, etc.

      Before the display file is allocated, the terminal should appear
      as, and simulate to the best of its ability, a Network Virtual
      Terminal (NVT).

      Any graphic commands issued before the allocation of a display
      file will be ignored.

      After requesting commands and receiving a structured display file,
      the following structure will exist:

         There will exist a subpicture, referred to as the ICP
         SUBPICTURE, whose rectangular extent corresponds to the extent
         of the virtual display allocated to this host.

         There will exist a tty-unit, referred to as the ICP TTY-UNIT,
         in the ICP SUBPICTURE, where rectangular extent corresponds to
         the extent of the virtual display allocated to this host.

            This tty-unit will consist of n lines, where n is terminal
            dependent and available through a query command.

            This tty-unit will be instituted for the display of
            unescorted characters.

         There will be in effect an implicit call on the ICP SUBPICTURE.

            This call is not accessible to the applications program.

         The applications program causes the display of information by:

            1) creating primitive units in the ICP SUBPICTURE

            2) creating call units, to created subpictures, in the ICP
               SUBPICTURE





Irby, et. al.                                                   [Page 8]

RFC 553        Draft design for a text/graphics protocol    14 July 1973


            3) using the TTY command to make visible/invisible the ICP
               TTY-UNIT (or change its location or size)

      After requesting and receiving a segmented display file, the
      following structure will exist:

         There will exist a segment, referred to as the ICP SEGMENT.

            There will exist a tty-unit, referred to as the ICP TTY-
            UNIT, in the ICP SEGMENT, whose rectangular extent
            corresponds to the extent of the virtual display allocated
            to this host.

            This tty-unit will consist of n lines, where n is terminal
            dependent and available through a query command.

            This tty-unit will be instituted for the display unescorted
            characters.

         The applications program causes the display of information by:

            1) creating primitive units in the ICP SEGMENT

            2) creating new segments

            3) using the TTY command to make visible/invisible the ICP
               TTY-UNIT (or to relocate it or change its size)

Display editing primitives

   General editing primitives

      REQUEST-DISPLAY-FILE (file-type)

         file-type is either structured or segmented.

         This command requires a response.

   Segmented display file editing

      SEGMENT (Segment)

         If the segment Segment already exists, then it is cleared; if
         it did not exist then it is created.

         Pictures are displayed within segments by the use of the
         primitive unit command listed below.




Irby, et. al.                                                   [Page 9]

RFC 553        Draft design for a text/graphics protocol    14 July 1973


      DELETE-SEGMENT(Segment)

         If the segment exists, then it is deleted.

      Primitive Units

         All unit operations cause immediate display on the screen.

         STRING-UNIT(Segment,Mode,X-Origin,Y-Origin,Text)

         Writes the specified string unit.

         Mode refers to relative intensity, blinking, reverse video,
         color, etc.

         Errors: Segment does not exist.

      LINE-UNIT(Segment,Type,Mode,X0,Y0,X1,Y1, ..., Xn,Yn)

         Draws the specified line segments.

         Type refers to solid, dashed, dotted, etc.

         Errors: Segment does not exist; illegal mode.

      DOT-UNIT(Segment,Mode,X0,Y0,X1,Y1, ..., Xn,Yn)

         Draws the specified dots.

         Errors: Segment does not exist; illegal mode.

      SPECIAL-POINTS-UNIT(Segment,Mode,X1,Y1, ..., Xn,Yn)

         Draws the special-points curve.

         The terminal should attempt to connect the specified points in
         the nicest way possible (e.g. Flegal's spline curve algorithm,
         straight line segments).

         Errors: Segment does not exist; illegal mode.

      TTY-UNIT(Segment,Mode,Rectangle,Lines)

         Creates a unit which will behave as a tty-simulation area with
         "lines" lines distributed within the specified rectangle.

         Unescorted characters will be echoed in this unit in addition
         to any other units they are being sent to.



Irby, et. al.                                                  [Page 10]

RFC 553        Draft design for a text/graphics protocol    14 July 1973


         Errors: Segment does not exist.

      DEVICE-SPECIFIC-UNIT(Segment,device commands)

         Creates a unit of device specific commands.

      TTY(parameters)

         parameters are:

            position rectangle, visible/invisible, number of lines, mode
            of characters

         This refers to the ICP TTY simulation.

      RESET()

         delete all segments, except ICP SEGMENT, and all units of ICP
         SEGMENT, except ICP TTY-UNIT

         resets all nodes to their initial state (i.e., the state that
         existed immediately after a REQUEST-DISPLAY-FILE command)

Structured display file editing

      SUBPICTURE(Subpicture, rectangle)

         Creates a new subpicture with name "Subpicture".  "rectangle"
         is the coordinates of a diagonal of the subpicture's virtual
         screen (i.e. its coordinate system.)

         If a subpicture named "Subpicture" already exists, it is
         cleared and the new coordinate rectangle takes precedence.

      DELETE-SUBPICTURE(Subpicture)

         Deletes the subpicture named "Subpicture".  Call units
         referring to Subpicture are also deleted.

      CLEAR-SUBPICTURE(Subpicture)

         Deletes all units of the subpicture Subpicture, but does not
         delete the subpicture.








Irby, et. al.                                                  [Page 11]

RFC 553        Draft design for a text/graphics protocol    14 July 1973


      Primitive Units

         All the operations for creating units are transparent to the
         prior existence of the designated unit, i.e. they function as
         "replace" as well as "create".

            STRING-UNIT(Subpicture,Unit,Target-Key,Mode,X-Origin,Y-
            origin,Text)

               Replaces the unit by a string unit.

               Mode specifies the mode of the characters (e.g. blinking,
               underlined, etc).

            Target-Key is used in conjunction with the TARGET-SENSITIVE
            command and target input.  It may also be sent via the SET-
            TARGET-KEY COMMAND.

            Errors: Subpicture does not exist; X-Origin or Y-Origin is
            outside the subpicture's virtual coordinate system.

               We explicitly do not require an error if the string
               extends beyond the right-hand edge of the subpicture;
               however, the results are not defined.

         LINE-UNIT(Subpicture,Unit,Target-Key,Type,Mode,X0,Y0,X1,Y1,
         ..., Xn,Yn)

            Replaces the unit by a line unit.

               Errors: Subpicture does not exist illegal mode; some X or
               Y is outside the subpicture.

         DOT-UNIT(Subpicture,Unit,Target-Key,Type,Mode,X0,Y0,X1,Y1, ...,
         Xn,Yn)

            Replaces the unit by a dot unit.

            Errors: Subpicture does not exist; illegal mode; some X or Y
            is outside the subpicture.

         SPECIAL-POINTS-UNIT(Subpicture,Unit,Target-Key,Type,Mode,X1,Y1,
         ..., Xn,Yn)

            Replaces the unit by a special-points unit.

            Errors: Subpicture does not exist; illegal mode; some X or Y
            is outside the subpicture.



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RFC 553        Draft design for a text/graphics protocol    14 July 1973


         CALL-UNIT(Subpicture,Unit,Target-Key,Called-
         Subpicture,Parameters)

            Replaces the unit by a call unit.

            Parameters:

               Master-Instance rectangles

               rotation

               mode

            Errors: Subpicture does not exist; Called-Subpicture does
            not exist; parameter errors.

         TTY-UNIT(Subpicture, unit, mode, rectangle, lines)

            Creates a unit which will behave as a tty-simulation area
            with "lines" lines distributed within the specified
            rectangle.

            Errors: Subpicture does not exist.

         DEVICE-SPECIFIC-UNIT(Subpicture, Unit, Target-Key, device,
         commands)

            Creates a unit of device specific commands.  The action of
            the commands should leave alone (or at least restore) any
            global modes, e.g., the standout mode (see below).

      APPEND-STRING-TO-UNIT(Subpicture, Unit, Text)

         Appends the specified text to the specific commands.  This only