rfc177.txt

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   control the display mode of the above where this is applicable.
   There are two mode items, the one governing vector modes, and one for
   character modes.  The quantities specified include brightness,
   blinking, color selection, and mode dependent descriptions.

   For vector modes, the texture of vectors such as dashed, solid or,
   dotted can be specified.  For characters, size, and orientation can
   be additionally specified.  The scope of a mode item extends to the
   next encountered mode item of the same type.  Mode specifications
   could have been included in the display items at the expense of more
   parameters and in possibly more data to be transmitted.  The mode
   specification consists of two eight bit bytes.  The bytes have the
   following organization:














McConnell                                                       [Page 5]

RFC 177    A DEVICE INDEPENDENT GRAPHICAL DISPLAY DESCRIPTION  June 1971


   1    4         3            2                     2    3
 +-----------------------+  +-----------------+   +-------------------+
 |    |    |             |  |     |           |   |     |     |       |
 |  B | BL |     CLR     |  | TX  |           |   | OR  |  SZ |       |
 |    |    |             |  |     |           |   |     |     |       |
 +-----------------------+  +-----------------+   +-------------------+

 BYTEO - both modes         BYTE 1- vector        BYTE 1- Character mode
                            mode

 Where      B     Blink if set

            BL    Brightness level - 0 = invisible, IIII brightness

            CLR   Color          One bit for each primary

            TX    Texture        OO = solid

                                 01 = dashed

                                 10 = dotted

                                 11 = dot - dash

           OR     Orientation binary value x 90deg

           SZ     Size

   If the device will ot support them, or provide subroutines to perform
   these enhanced functions, they are treated as NOPs.

   Thus the NGDL is a set of named lists.

      DEFINE IMAGE AREA (command = 2) has three parameters a 16 bit area
      name; an (x,y) pair defining the lower left corner of the area and
      an (x,y) pair defining the upper right corner.  If the name has
      already been used to define an area then this command serves a
      re-definition of that area.  If the two (x,y) information
      displayed in it.  If X1 is greater than Xr or Y1 is greater than
      Yr then the definition is treated as NOP.

      The following commands are included to avoid retransmission of a
      list when some minor changes to it are necessary.  All instances
      of a list, where an instance is a command to execute the list will
      be effected.  Where a list has been copied into another list, no
      change will take place in the copied list.





McConnell                                                       [Page 6]

RFC 177    A DEVICE INDEPENDENT GRAPHICAL DISPLAY DESCRIPTION  June 1971


      TRANSLATE LIST (command = 3) provides for translation of all
      instances of a list within all of the image spaces it occurs in.
      Parameters are the 16 bit list name, and two 16 fractions for the
      coordinate values of the translation.

      SCALE LIST (command = 4) can change the size of the picture
      created by a list in all image spaces.  The parameters are the 16
      bit list name followed by two 16 bit (X,Y) unsigned fractions with
      eight bits of exponent followed by eight bits of mantissa.  These
      alter the scale factors in the X and Y directions.

      ROTATE LIST (command = 5) will rotate all instances of a list.
      The parameters are for the 16 bit list name, and a 16 bit value
      corresponding to rotational angle in degrees with the sense being
      counter-clockwise for increasing values and the possible axis
      being zero degrees.

   The NGLI executes in a loop, taking items from the main list.  When
   the end of the main list is reached, the NGLI returns to the top of
   it.  At any point, the NGLP gives the NGLI the positional
   displacement of the next display item it is processing.  When a
   display item of the type h. is encountered, the current lists's
   execution is suspended,  the name of the list, the current origin,
   and the NGLP are saved in the NGES.  The NGLP is re-set to zero, the
   next current origin is calculated, and execution of the new list
   commences.  When the end of the list is encountered, the old values
   are restored from the NGES and execution of the suspended list
   continues.  The NGLI is then a recursive interpreter.  Whenever a new
   image area is opened, the name of that image area is stored in the
   current image area name.

   The problem of interacting with the displayed picture has yet to be
   addressed since this is a more complicated area.  Interaction may
   occur in two fashions:  the first, and the easiest to handle, are
   those kinds of events which are separate from the picture itself.
   This encompasses key boards and function key types of devices.  These
   can be handled as standard messages from the graphics device to the
   serving host.  The second class of interactions is with the picture
   itself.  This is more difficult because of the problem of associating
   the point selected with some meaningful entity such as a list.  This
   association can probably only be made by the serving host since the
   using host, or a Form Machine, may have transformed the NGDS in
   unknown ways, and the NGDS may no longer exist at the using host's
   site.

   There are essentially two classes of devices that can interact with
   the picture.  The first class is synchronous devices, ones who only
   cause some attention to occur while a given display item is being



McConnell                                                       [Page 7]

RFC 177    A DEVICE INDEPENDENT GRAPHICAL DISPLAY DESCRIPTION  June 1971


   executed.  Light pens are synchronous devices.  Asynchronous devices
   are those which can interact regardless of which, or even when no,
   display item is being executed.  Asynchronous devices make
   associations more difficult since no relationship can be easily
   inferred as they can for synchronous devices.

   The NGES is created for the interaction with the picture.  For
   synchronous devices the current values for the list name, origin, and
   NGLP, as well as the contents of the NGES provides a hierarchical
   structure where associations can be made.  For asynchronous devices,
   the structure is probably not as necessary as the name and
   coordinates within the image space in which the interaction occurred.
   It will be necessary for the using host to understand which type of
   devices are available and to supply proper type of interaction
   information to the serving host.

   The form of the interaction information for synchronous devices
   follows:


INTERACTION (type, cia, cln, cor, clp, n, l1, or1, lp1, ...ln, orn, lpn)

   Where type describes the interaction type 0=synchronous
   cia     current image area name
   cln     current list name
   cor     current origin value
   clp     current NGLP value
   n       number of entries in NGES, higher value of n is older entry
   li      list name of the i th entry
   ori     origin of the i th entry
   lpi     NGLP of the i th entry

   The form for asynchronous i.. teraction is:

   INTERACTION (type, cia, iax, iay, sx, sy)

   Where type = 1 for asynchronous interactions
   cia     current image name
   iax     image area x coordinate
   iay     image area y coordinate
   sx,sy   screen x,y coordinates










McConnell                                                       [Page 8]

RFC 177    A DEVICE INDEPENDENT GRAPHICAL DISPLAY DESCRIPTION  June 1971


NETWORK  |    Using Host
         |                +-------+
         |                |       |
         |                | NGDL  |          +--------+       +-------+
         +--------+       |       |--------->|        |       |       |
         |        |------>|       |          |  NGLI  |------>|  NGS  |
         |  NGDS  |       +-------+          |        |       |       |
         |        |       +-------+          |        |       |       |
         |        |------>|       |--------->|        |       +-------+
         +--------+       |IMAGE  |          +--------+
         |                |AREA   |              ^
         |                |DEFINI-|              |
         |                |TIONS  |              V
         |                +-------+          *--------+
         |                                   |  NGLES |
         |                                   |    &   |
         |                                   |  NGLP  |
         |                                   +--------+











        [This RFC was put into machine readable form for entry]
    [into the online RFC archives by Kelly Tardif, Viag閚ie 12/1999]




















McConnell                                                       [Page 9]