rfc184.txt

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   On a Gould Electrostatic Printer-Plotter, for example, the system
   would expect to have dot patterns with which to fill areas in order
   to simulate the greys.  For purposes of other displays, a SETSQUARES
   procedure should be available so that the user can specify various
   kinds of cross- hatching and character filling to apply to the grid
   areas.

   To enter an item of data the procedure is

                                              1 <= I <= N
                  GRIDAREA(I, J, LEVEL)       1 <= J <= M
                                              1 <= LEVEL <= IRNGE

   where I and J select an area on the grid, and LEVEL tells how to fill
   it.  Obviously, for this kind of display mode some provision must be
   made to end the picture because the servicing routine will have to
   work on it from either the top or the bottom in a sweep mode.  A
   procedure call of GRIDAREA(0, 0, 0) will terminate it.  The GRIDAREA
   mode is very similar to the following, MATRIXAREA, with the primary
   difference being that the specification of areas is random and areas
   which are not specified will be left blank.






Kelley                                                          [Page 4]

RFC 184              Proposed Graphic Display Modes          6 July 1971


   MATRIXAREA            The user specifies an area size and a "pseudo-
   ----------            character" set, then writes from left to right,
                         top to bottom, much like a line printer, using
                         bytes to specify which of his "pseudo-character"
                         set to use.

The initializing call is MATRIXSET(N, M, DEFINITION, CODE)

The display mode is raster                ________________________
oriented, and each "pseudo-              |  _   _   _   _   _   _ |
character" will be on a N x M            | |_| |_| |_| |_| |_| |_||
matrix of dots.  (A later                |  _   _   _             |
embellishment for printers               | |_| |_| |_| . . .      |
would include matrix of characters.)     |  _   _                 |
Parameters DEFINITION and CODE           | |_| |_| . . .          |
are both arrays, used together to        | .    \ \               |
specify the "pseudo-character" set.      | .     \  \             |
DEFINITION is packed with bits           |________\___\___________|
according to the following scheme:                \     \
                                                   \      \
                                                    \    __\_______
                                                     \  /           \
                                                      \/  ________   \
                                                      /   |_|_|_|_|   \
                                                     /    |_|_|_|_|    \
                                                     |    |_|_|_|_|    |
                                                     |    |_|_|_|_|    |
                                                     \    |_|_|_|_|    /
                                                      \   |_|_|_|_|   /
                                                       \             /
                                                        \___________/

     n - bits
    +--+--+--+--+
    |XX|  |  |XX|
    |--|--|--|--|
s   |  |XX|XX|  |
t   |--|--|--|--|
i   |XX|  |  |XX|
b   |--|--|--|--        +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--\
    |  |XX|XX|  |  <=== |1|0|0|1|0|1|1|0|1|0|0|1|0|1|1|0|1|0|0|1|0|1|1|0|\
-   |--|--|--|--|       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-\
m   |XX|  |  |XX|        \--v--/ \--v--/ \--v--/ \--v--/ \--v--/ \--v--/
    |--|--|--|--|           n       n       n       n       n       n
    |  |XX|XX|  |
    +--+--+--+--+        \-------------------------v---------------------/
                                                   m-groups




Kelley                                                          [Page 5]

RFC 184              Proposed Graphic Display Modes          6 July 1971


   The bit stream for the definition is irrespective of word boundaries.
   We leave it up to the MATRIXSET routine to be able to undo this.
   Obviously, for user convenience we have some standard sets they can
   use to save having to define their own, and if they want to define
   their own, we make routines to ease the pain.

   The array CODE, on the other hand, is a byte-stream, i.e., a stream
   of eight-bit groups of bits which will correspond to each of the
   groups of (N x M)-bits.  This allows 256 pseudocharacters for one
   set.

   To enter an item of data in this mode the procedure is

                  MATRIXAREA(ARRAY, LENGTH)

   ARRAY is a buffer location and length is the number of code bytes
   which are to be put out.  Each call will put out one row of the
   display.  Unused bytes at the end of the stream (bytes left over in
   the last word) should be zero.  Any codes in excess of the maximum
   number allowed on a line will be discarded.

   It should be noted that this routine is nominally used for special
   character sets, or for that matter, any character sets that are
   software generated on dot-raster devices.  In addition, however, it
   can be used for photomosaic displays, area filling on maps, and
   development of capability of producing audiovisual aids for
   presentations.


   SCANLINE               A raster-scanning display mode for which the
   --------               user specifies a raster size, number of grey
                          levels needed, and direction of scan.  The
                          subsequent data items specify only the location
                          and character of a change in the scanning
                          beam (or program).

   The initializing procedure is SCANLINESET(DELTA, LEVELS, ORGMODE)

   DELTA is an integer specifying the number of display points to be
   included in each step.  LEVELS denotes the number of intensity levels
   to be used, and the sign of ORGMODE specifies whether the scan is to
   be from the bottom up (plus) or top down (minus) on the display.  For
   both cases we will assume left-to-right.  The absolute value of
   ORGMODE gives the starting Y position.

   All subsequent calls to this routine are of the form

                          SCANLINE(X, INTENSITY)



Kelley                                                          [Page 6]

RFC 184              Proposed Graphic Display Modes          6 July 1971


   The first such call denotes the origin in X and the initial
   intensity.  Subsequent calls denote the X value of the next point on
   the scan where the intensity is to change, and that new intensity.
   The program (or device) takes care of the stepping of the scan by
   DELTA across the page, with the current intensity.  Thus, the program
   (device) only needs a data item for each change in the scan, not for
   each position.  When the next X is less than the previous X, or the X
   position has been stepped to its limit, the Y position in the
   incremented or decremented to continue the scan on the next line.

   We see the device which accepts such a display as accepting a stream
   of triplets of bytes, where the first two bytes (16 bits) specify the
   X and the third (8 bits) specifies the level.  The end of the stream
   would be specified by three bytes of deletes (all ones).  This
   display mode is implemented in hardware on the display at the
   Coordinated Science Laboratory at this University.  It is the same
   one which was used for the grey-scale work which has been reported by
   Bouknight.


   SCANPOINT            A point with intensity scanning mode in which
   ---------            the scan is handled automatically and only the
                        intensity of each point needs to be transmitted
                        to the program (device).

   The initializing call for this procedure is

           SCANPOINTSET(DELTA, LEVELS, ORGMODE)

   The arguments are the same as for SCANLINE.  The difference is in the
   meaning of subsequent calls.  The origin for the scan is at the left
   end of the line corresponding to the absolute value of ORGMODE.  The
   stepping is done from left to right and at the end of each line, the
   Y position is incremented or decremented by DELTA, according to the
   sign of ORGMODE.

   Subsequent calls to this procedure are of the form SCANPOINT(LEVEL)
   where LEVEL denotes the intensity level at which the next point is to
   be displayed.  In this mode every point must have its intensity
   specified by a separate call to the routine (byte to the device).
   However, beyond the starting point no position information is
   required.


       [ This RFC was put into machine readable form for entry ]
        [ into the online RFC archives by Hamid Dastkar 09/99 ]





Kelley                                                          [Page 7]