Date: 1 July 1980 14:57-EDT
From: George J. Carrette <GJC at MIT-MC>
To: "(FILE [GJC;GRAPHS USAGE])" at MIT-MC

    Date: 1 July 1980 14:53-EDT
    From: George J. Carrette <GJC at MIT-MC>
    To: MEM at MIT-MC, JGA at MIT-MC
    cc: "(FILE [FILE GJC;GRAPHS USAGE])" at MIT-MC


    The generic functions are

    set-pen, move-pen, vector-pen, draw-point, draw-line.

    set-window, set-viewport, get-window, get-viewport.

    The first argument to these functions is always a graphic object.
    The rest of the arguments are always paired X,Y. e.g.
    (set-pen foo x y) and (draw-line foo x1 y1 x2 y2).
    The coordinate arguments can either be numbers, arrays of numbers,
    or lists of numbers.

    (make-ards-stream) makes you an ards-object.
    (make-graphics-stream <ards-object>) takes an ards-object and returns
    a flonum-scaling graphics stream.

    Other operations are conviently accessed with the CALL function.

    (call <stream> 'cursorpos 'c)
    (call <stream> 'which-operations)
    (call <stream> 'open 'tty)
    (call <stream> 'open 'dsk '((foo) bar >))
    (call <stream> 'close)

    No compile-time considerations are needed when using the generic operators.
    However, users of call should do (or (get 'closure 'version) (load '((gjc)close)))
    at eval and compile times.



 A graphics stream is a special object which these generic functions
 can operate on. These objects keep an internal state, such as
 the position of the last point plotted, and the values of the
 scaling factors.

 Loading GJC;GRAPHS FASL will make the the relevant functions
 autoloading. Functions for hardware specific objects are in
 different files.

 See GRAPHZ DEMO for example usage.

 (MAKE-ARDS-STREAM) returns an object which takes fixnum arguments
 and outputs ARDs graphics codes to file or TTY objects which it
 stores internaly. This is a primitive stream.

 (MAKE-TEK-STREAM) is not yet implemented.

 (MAKE-GRAPHICS-STREAM <OUTPUT-STREAM>) takes a primitive stream
 as argument and returns a stream which can do floating point
 scaling and clipping, and setting of windows and viewports.

 (GRAPHICS-STREAM-OPEN <STREAM> <MODE> &OPTIONAL <ARG>)
 <mode> is 'TTY or 'DSK. <arg> is the file name when opened
 in 'DSK mode.

 (GRAPHICS-STREAM-CLOSE <STREAM>) closes any DSK file.

 (SET-PEN <GRAPHICS-STREAM> X Y)

 (MOVE-PEN <GRAPHICS-STREAM> X Y) 
 draws a line from the last point the new point.

 (VECTOR-PEN <GRAPHICS-STREAM> X Y) does a relative move of the pen.

 (DRAW-POINT <GRAPHICS-STREAM> X Y) draws a line of length 0.

 (GRAPHICS-STREAM-TYO <STREAM> <ARG>) presently does a character
 TYO. Does not try and enforce clipping. #\CR may cause lossage.
 Line-drawing of characters and scaling may be supported in the
 future.

 The following are not supported in primitive graphic streams.

 (SET-WINDOW <GRAPHIC-STREAM> X0 X1 Y0 Y1)
 the window is the apparent flonum size.

 (SET-VIEWPORT <GRAPHIC-STREAM> X0 X1 Y0 Y1)
 The viewport is set in "hardware" or rather, primitive stream
 dependant, fixnums.
 The default values for these are usually reasonable, by definition.

 (MAKE-GRAPHICS-SFA <GRAPHICS-STREAM>) takes a graphics stream
 and returns and SFA which may be used as an argument to
 PRINT, FORMAT, etc.

 (MAKE-TRACED-FUNCTOR <FUNCTOR>) takes a functor (a graphics stream is
 a functor) and returns a functor which is traced. Trace information
 is output to the value of TRACED-FUNCTOR-MSGFILE which should NOT be
 a stream which calls any traced functors! The returned functor is
 not equal to the argument, i.e. the argument is not side effected.