Simple Graphics Package (SGP) Documentation
             -------------------------------------------


         Documentation and Software Written by Kevin Rosenberg
                  Copyright (c) 1984, Kevin Rosenberg





                            OVERVIEW
                            --------

                       +------------------------+
                       | World Coordinate level |
                       +-----------+------------+
                                   |
                                   |
                      +------------+-------------+
                      | Convert to Normalized    |
                      | device coordinates (NDC) |
                      +------------+-------------+
                                   |
                                   |
                            +------+-------+           +--------------+
                            | Segmentation +-----------+ Disk Storage |
                            +------+-------+           +--------------+
                                   |
                      +------------+-------------+
                      | Convert to Physical      |
                      | device coordinates (PDC) |
                      +--------------------------+


World Coordinate Level
----------------------
     initgrf2 ()                         Initialize 2 dimensional graphics
     termgrf2 ()                         Terminate 2 dimensional graphics
     window2  (xmin, ymin, xmax, ymax)   Set window for world coord
     viewprt2 (xmin, ymin, xmax, ymax)   Viewport for window in NDC
     moveabs2 (x, y)                     Move graphics cursor
     moverel2 (dx, dy)
     pntabs2 (x, y)                      Plot point at current position
     pntrel2 (dx, dy)
     lineabs2 (x, y)			 Draw line from current point to point
     linerel2 (dx, dy)
     markabs2 (x, y)                     Draw marker at current position
     markrel2 (dx, dy)
     polylnabs (x[], y[], n)             Draw a set of lines
     polylnrel (dx[]. dy[]. n)
     wc_to_ndc (xwc, ywc, xndc, yndc)    Convert from world coord to NDC
     ndc_to_wc (xndc, yndc, xwc, ywc)    Convert from NDC to world coord
     drawtext (str)                      Draw text string at current positon

     INTERNAL:
          calc_map ()                        Calculate wc to ndc factors
          clip(rectangle[4], x1, y1, x2, y2) Clip a line againt rectangle


Normalized Coordinate level
--------------------------
     stylus (x, y, beam)                 Draw a line from current position
     opendevice (device)                 Open a device for output
     closedevice (device)                Close a device for output
     flushdevice (device)                Put all pending data on device
     inqdev (device, xmax, ymax)         Return data on device
     setcolor (color)			 Set current drawing color
     setlinestyle (style)                Set current line style
     setlinewidth (width)                Set current line width
     settext (h, w, orientation, dir, font)  Set text attributes
     settextclr (foreground, background) If back=-1, then transparent backg
     inqtext(h, w, o, dir, font, fore, back) Get current text attributes
     charndc (c, xndc, yndc)             Draw char at NDC position
     textndc (str, xndc, yndc)           Draw text string at NDC position

     setmarker (marker_type, color)      Set marker attibutes
     markndc (xndc, yndc)                Draw marker at NDC position

     ndc_to_pdc (device, xndc, yndc, xpdc, ypdc)
     savescrn (filename, xmin, ymin, xmax, ymax)
     readscrn (filename)

Physical Device Level
---------------------
     crtdot (x, y, c)
     crtline (x1, y1, x2, y2, color, style)
     wrtchar (char, x, y, dotfunc())
     wrttext (str, x, y, dotfunc())

     readblock (array, xmin, ymin, xmax, ymax)
     writeblock (array, xmin, ymin, mode)

     prtdot (x, y, c)
     prtline (func, x1, y1, x2, y2, color, style)


Input Functions
---------------
Physical device level
     joystk (sticknum, x, y)

Normalized Coordinate level
     readloc (xndc, yndc)
     inithcur (height, width, color)	     Initialize haircross cursor
     movhcurabs (xndc, yndc)                 Move haircross cursor to point
     movhcurrel (dxndc, dyndc)               Move relatively
     termhcur ()			     Turn off haircross cursor
     readpnt (xndc, yndc)		     Have cursor track joystick
					     User press button at desired point

                                DATA STRUCTURES
                                ---------------
struct DEVICE {
     int xsize, ysize;                  Size of device in pixels
     int xmax, ymax;			Maximum coordinates
     int colormax;                      Maximum color number of device
     int style;                         Current linestyle of device
     int width;                         Current width of device
     int color;                         Current color of device
     int curx, cury;                    Current position
     int charwidth, charheight;         Size of characters in pixels
     float aspt                         Aspect ratio  Multiple coord 
     int (*dot)();                      Dot function for device
     int (*line)();			Line function for device
     int mode;                          Device mode
};

struct CHARSPEC {
     float width, height;               size of characters in NDC
     int dirflag, orientflag            text direction, character orientation
     int fore, back;                    foreground & background color
};

struct CURRENT {
    int color;
    int linestyle;
    int linewidth;
    float xndc, yndc;
}

            Map directly from world coords to physical device coords
            --------------------------------------------------------

Window:   xwmin, xwmax, ywmin, ywmax
Viewport: xvmin, xvmax, yvmin, yvmax
Physical: xpmax, ypmax

To convert from wc to ndc:
     xndc = xvmin + (xwc - xwmin) / (xwmax - xwmin)
     yndc = yvmin + (ywc - ywmin) / (ywmax - ywmin)

To convert from ndc to pdc:
     xpdc = xndc * xpmax
     ypdc = yndc * ypmax

So, for each device set up the following composite transformation:
     xpdc = xpmax * (xvmin + (xwc - xwmin) / (xwmax - xwmin))
     ypdc = ypmax * (yvmin + (ywc - ywmin) / (ywmax - ywmin))

     xpdc = xpmax * xvmin + (xwc - xwmin) * (xpmax / (xwmax - xwmin))
          = xadd + (xwc - xsub) * xfact

Characters
----------
     Fonts:
          NORMAL              Regular character set
          BOLD                Overstike chars with x offset by 1 pixel
          ITALICS             Shear characters along character height

                       NORMAL   BOLD    ITALICS
                         X       XX         X
                        XXX     XXXX      XXX
                       X   X   XX  XX    X   X
                       X   X   XX  XX    X   X
                       XXXXX   XXXXXX   XXXXX
                       X   X   XX  XX   X   X
                       X   X   XX  XX   X   X