rfc746.txt

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NWG/RFC# 746                                         RMS 17-MAR-78 43976
The SUPDUP Graphics Extension



Commands:

   Commands to draw an object always have counterparts which erase the
   same object.  On a bit matrix terminal, erasure and drawing are
   almost identical operations.  On a display list terminal, erasure
   involves searching the display list for an object with the specified
   characteristics and deleting it from the list.  It is assumed that
   any terminal whose %TOERS bit is set can erase graphic objects.

   The commands to draw objects run from 100 to 137, while those to
   erase run in a parallel sequence from 140 to 177.  Other sorts of
   operations have command codes below 100.  Meanwhile, the 20 bit in
   the command code says which type of addresses are used as arguments:
   if the 20 bit is set, absolute addresses are used.  Graphics commands
   are given names starting with "%GO".

   Graphics often uses characters.  The %GODCH command is followed by a
   string of characters to be output, terminated by a zero.  The
   characters must be single-position printing characters.  On most
   terminals, this limits them to ASCII graphic characters.  Terminals
   with %TOSAI set in the TTYOPT variable allow all characters 0-177.
   The characters are output at the current graphics cursor position
   (the lower left hand corner of the first character's rectangle being
   placed there), which is moved as the characters are drawn.  The
   normal type-out cursor is not relevant and its position is not
   changed.  The cursor position at which the characters are drawn may
   be in between the lines and columns used for normal type-out.  The
   %GOECH command is similar to %GODCH but erases the characters
   specified in it.  To clear out a row of character positions on a bit
   matrix terminal without having to respecify the text, a rectangle
   command may be used.

   Example:

      The way to send a simple line drawing is this:

         %TDRST                 ;Reset all graphics modes.
         %TDGRF                 ;Enter graphics.
         %GOCLR                 ;Clear the screen.
         %GOMVA xx yy           ;Set cursor.
         %GODLA xx yy           ;Draw line from there.
         << repeat last two commands for each line >>
         %TDNOP                 ;Exit graphics.









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NWG/RFC# 746                                         RMS 17-MAR-78 43976
The SUPDUP Graphics Extension



Graphics Input:

   The %TRGIN bit in the right half of the SMARTS variable indicates
   that the terminal can supply a graphic input in the form of a cursor
   position on request.  Sending a %GOGIN command to the terminal asks
   to read the cursor position.  It should be followed by an argument
   character that will be included in the reply, and serve to associate
   the reply with the particular request for input that elicited it.
   The reply should have the form of a Top-Y character (code 4131),
   followed by the reply code character as just described, followed by
   an absolute cursor position.  Since Top-Y is not normally meaningful
   as input, %GOGIN replies can be distinguished reliably from keyboard
   input. Unsolicited graphic input should be sent using a Top-X instead
   of a Top-Y, so that the program can distinguish them.  Instead of a
   reply code, for which there is no need, the terminal should send an
   encoding of the buttons pressed by the user on his input device, if
   it has more than one.

Sets:

   Terminals may define the concept of a "set" of objects.  There are up
   to 200 different sets, each of which can contain arbitrarily many
   objects.  At any time, one set is selected; objects drawn become part
   of that set, and objects erased are removed from it.  Objects in a
   set other than the selected one cannot be erased without switching to
   the sets that contain them.  A set can be made temporarily invisible,
   as a whole, without being erased or its contents forgotten; and it
   can then be made instantly visible again.  Also, a whole set can be
   moved.  A set has at all times a point identified as its "center",
   and all objects in it are actually remembered relative to that
   center, which can be moved arbitrarily, thus moving all the objects
   in the set at once.  Before beginning to use a set, therefore, one
   should "move" its center to some absolute location.  Set center
   motion can easily cause objects in the set to move off screen.  When
   this happens, it does not matter what happens temporarily to those
   objects, but their "positions" must not be forgotten, so that undoing
   the set center motion will restore them to visibility in their
   previous positions.  Sets are not easily implemented on bit matrix
   terminals, which should therefore ignore all set operations (except,
   for a degenerate interpretation in connection with blinking, if that
   is implemented).  The %TQSET bit in the SMARTS variable of the
   terminal indicates that the terminal implements multiple sets of
   objects.

   On a terminal which supports multiple sets, the %GOCLR command should
   empty all sets and mark all sets "visible" (perform a %GOVIS on each
   one).  So should a %TDCLR SUPDUP command.  Thus, any program which
   starts by clearing the screen will not have to worry about
   initializing the states of all sets.



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NWG/RFC# 746                                         RMS 17-MAR-78 43976
The SUPDUP Graphics Extension



Blinking:

   Some terminals have the ability to blink objects on the screen. The
   command %GOBNK meaning make the current set blink.  All objects in it
   already begin blinking, and any new objects also blink.  %GOVIS or
   %TOINV cancels the effect of a %GOBNK, making the objects of the set
   permanently visible or invisible.  %TQBNK indicates that the terminal
   supports blinking on the screen.

   However, there is a problem:  some intelligent bit matrix terminals
   may be able to implement blinking a few objects, if they are told in
   advance, before the objects are drawn.  They will be unable to
   support arbitrary use of %GOBNK, however.

   The solution to the problem is a convention for the use of %TOBNK
   which, together with degenerate definitions for set operations, makes
   it possible to give commands which reliably work on any terminal
   which supports blinking.

   On a terminal which sets %TQBNK but not %TQSET, %GOBNK is defined to
   cause objects which are drawn after it to be drawn blinking. %GOSET
   cancels this, so following objects will be drawn unblinking. This is
   regardless of the argument to the %GOSET.

   Thus, the way for a program to work on all terminals with %TQBNK,
   whether they know about sets or not, is:  to write a bliniking
   picture, select some set other than your normal one (set 1 will do),
   do %GOBNK, output the picture, and reselect set 0.  The picture will
   blink, while you draw things in set 0.  To draw more blinking
   objects, you must reselect set 1 and do another %GOBNK.  Simply
   reselecting set 1 will not work on terminals which don't really
   support sets, since they don't remember that the blinking objects are
   "in set 1" and not "in set 0".

   Erasing a blinking object should make it disappear, on any terminal
   which implements blinking.  On bit matrix terminals, blinking MUST
   always be done by XORing, so that the non-blinking background is not
   destroyed.

   %GOCLS, on a terminal which supports blinking but not sets, should
   delete all blinking objects.  Then, the convention for deleting all
   blinking objects is to select set 1, do a %GOCLS, and reselect set 0.
   This has the desired effect on all terminals.  This definition of
   %GOCLS causes no trouble on non-set terminals, since %GOCLS would
   otherwise be meaningless to them.

   To make blinking objects stop blinking but remain visible is possible
   with a %GOVIS on a terminal which supports sets.  But in general the
   only way to do it is to delete them and redraw them as permanent.



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NWG/RFC# 746                                         RMS 17-MAR-78 43976
The SUPDUP Graphics Extension



Rectangles and XOR

   Bit matrix terminals have their own operations that display list
   terminals cannot duplicate.  First of all, they have XOR mode, in
   which objects drawn cancel existing objects when they overlap.  In
   this mode, drawing an object and erasing it are identical operations.
   All %GOD.. commands act IDENTICALLY to the corresponding %GOE..'s.
   XOR mode is entered with a %GOXOR and left with a %GOIOR.  Display
   list terminals will ignore both commands.  For that reason, the
   program should continue to distinguish draw commands from erase
   commands even in XOR mode.  %TQXOR indicates a terminal which
   implements XOR mode.  XOR mode, when set, remains set even if
   graphics mode is left and re-entered.  However, it is wise to
   re-specify it from time to time, in case output is lost.

   Bit matrix terminals can also draw solid rectangles.  They can thus
   implement the commands %GODRR, %GODRA, %GOERR, and %GOERA.  A
   rectangle is specified by taking the current cursor position to be
   one corner, and providing the address of the opposite corner.  That
   can be done with either a relative address or an absolute one.  The
   %TQREC bit indicates that the terminal implements rectangle commands.

   Of course, a sufficiently intelligent bit matrix terminal can provide
   all the features of a display list terminal by remembering display
   lists which are redundant with the bit matrix, and using them to
   update the matrix when a %GOMSR or %GOVIS is done.  However, most bit
   matrix terminals are not expected to go to such lengths.

























                                  -9-

NWG/RFC# 746                                         RMS 17-MAR-78 43976
The SUPDUP Graphics Extension



How Several Process Can Draw On One Terminal Without Interfering With
Each Other:

   If we define "input-stream state" information to be whatever
   information which can affect the action of any command, other than
   what is contained in the command, then each of the several processes
   must have its own set of input-stream state variables.

   This is accomplished by providing the %GOPSH command.  The %GOPSH
   command saves all such input-stream information, to be restored when
   graphics mode is exited.  If the processes can arrange to output
   blocks of characters uninterruptibly, they can begin each block with
   a %GOPSH followed by commands to initialize the input-stream state
   information as they desire.  Each block of graphics output should be
   ended by a %TDNOP, leaving the terminal in its "normal" state for all
   the other processes, and at the same time popping the what the %GOPSH
   pushed.

      The input-stream state information consists of:

         The cursor position
         the state of XOR mode (default is OFF)
         the selected set (default is 0)
         the co-ordinate unit in use (physical dots, or virtual)
            (default is physical)
         whether output is going to the display screen or to a hardcopy
            device (default is to the screen)
         what portion of the screen is in use
            (see "Using Only Part of the Screen")
            (default is all)

   Each unit of input-stream status has a default value for the sake of
   programs that do not know that the information exists; the exception
   is the cursor position, since all programs must know that it exists.
   A %TDINI or %TDRST command should set all of the variables to their
   default values.

   The state of the current set (whether it is visible, and where its
   center is) is not part of the input-stream state information, since
   it would be hard to say what it would mean if it were.  Besides, the
   current set number is part of the input-stream state information, so
   different processes can use different sets.  The allocation of sets
   to processes is the server host's own business.









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