Oakland CPM Archive/oakcpm.iso/cpm/pascal-p/plotter.lbr/PLOTTER.DZC/PLOTTER.DOC

Text File | 1987-02-07 | 8.0 KB | 193 lines

             PLOTTER subsystem - by C.B. Falconer

The file PLOTTER.INC may be included in a PascalP source program with
"(*$i'plotter.inc'*), and provides:

       A 900 (wide) by 640 (deep) bit field, which will appear
       as a 7 1/2 inch by 8 inch field on an Epson printer.

       The ability to set any dot in the field, to write lines
       from the "current" position to any other position;  to
       reposition the "pen" at any position (by writing a line
       with no ink); and to write graphics characters, described
       by a Hershey font file, at any location and at any angle,
       and with any scale factor.

The field size may be modified by altering the constant HDOTS (for the
width), and MAXSTRIPS (for the height).  The height is always MAXSTRIPS
times 8 dots, and this value is available in VDOTS : integer (but ONLY
after plotopen is called.

The constants VDPI and HDPI (vertical/horizontal dots per inch) are
used to modify the Hershey fonts for the proper form factors.  These are
set for the Epson printers.  ONLY after plotopen is called, the ratio is
available in ASPECT : real.

The values in XNOW, YNOW, VDOTS, ASPECT may be used, but should NOT be
altered by the application program.

The file TESTPLOT.PAS is a demonstrator, and allows the user to specify
lines and character strings to write.  It automatically creates an outline
border.  Use this as a usage example.

In general, before using the system the procedure PLOTOPEN must be called

              plotopen

to initialize.  If graphics characters are to be written the font must be
loaded by:
              loadfont(VAR f : text)

where f is the text file holding the font.  Note that the font may be
changed on the fly by reloading a new font.  The font may be loaded before
or after calling plotopen.  Loadfont reads the file from the beginning.

All plotting (except PLOTDOT) is done in terms of an imaginary pen position.
Lines are drawn from the present position to a specified new position, with
or without marking the "paper".  The call is:

              plotline(ink : boolean; x, y : integer)

where ink false causes no paper marking.  x and y are the final absolute
pen location.  At least one dot will be made when ink is true.

The variables XNOW and YNOW (: integer) always hold the current pen position.

The primitive

              plotdot(x, y : integer)

allows other subsystems to interface, such as arc generators.

To plot a character (which is in the loaded font), the call is:

              plotchar(ch : char; x, y : integer;
                       height, compress, angle : real);

where x,y is the starting location, height is the relative height (usually
in the range 0.5 to 2.0), compress (usually 1) specifies horizontal
compression/expansion (values less than 1 specify compression), and angle
(in radians) specifies counter-clockwise rotation of the x axis for the
character.  At completion xnow/ynow will be a suitable location for the
next character at the same angle.  A space uses the horizontal size of the
first character in the font (usually 'A') and simply moves.

Plotchar uses the 'aspect' value to correct distortions in the font caused
by different vertical and horizontal dot densities.

At completion of the drawing, to write the output to either a disk file or
the listing device (an Epson printer), do

              plotclose(VAR f : text);

where f is the already opened file to write to.  This allows multiple
drawings to be emitted to the same file.

WARNING: If a disk file is created that file will contain many non-printing
characters whose interpretation is not the usual.  To print it must be
copied totally unchanged to the printer.  Program LIST can do this.

NOTE: Both the virtual memory (temporary) file, and the output file, will
contain about 71 K bytes.  The virtual file is created on the default drive,
but the output file may be controlled at run time.  The application may
remove the virtual file with "purge(stripfile)" at completion, if desired.


Fonts
=====

The font files consist of a series of entries, consisting of:

* The character 'C'
  The character to be plotted

and the remainder of the entry is a series of integers, separated by
spaces or <eolns>

* The standard Hershey identification number for the graphic.
  the height of the character (2 digits)
  the width  of the character (2 digits)
* the width for non-proportional writing (2 digits)
  <eoln>

followed by a series of 4 or 5 char. integers, max 10 per line,
specifying RELATIVE pen positions (offset by 10 for x, by 35 for y).
If the integer is negative it specifies that no marks are to be
made in moving to this position, otherwise "ink" is used.  The rest
of the integer is interpreted as its absolute value (i.e. after
discarding any - sign).  If the value is >= 10000 it is the last
for the character (and eoln follows).  The right two digits are a
"y" position, and the left two (ignoring any 10000) are the "x"
position.  These are alway relative to the starting position for
the character, after subtracting the above offsets.

The fields marked with "*" are not used by this software, and thus
may be anything.  However they must be present in the file or the
load process will fail.

This allows custom fonts to be generated and used as desired.
The three fonts supplied (font1, font2, and font3) require successively
more processing, and are successively elegant.  They contain the
characters 'A' thru 'Z', 'a' thru 'z', '0' thru '9'.


PascalP PCD vs COM files
========================

Since most of the time is spent in system procedures (file i/o, real
arithmetic, and trigonometric functions) minimum speed improvements
result from the use of .COM files rather than the machine independant
.PCD files.  Time ratios will be in the order of 2:1 to 3:2.


Other systems
=============
Most of the code is in ISO standard Pascal, and thus should port with
no difficulty.  The declarations may have to be inserted in the appropriate
portion of the application for systems other than PascalP (which allows
complete modularizaation).  Other points are discussed below, and potential
problem areas are marked with '{}' in the first column of the source.


Other printers
==============

The output interface is entirely specified in PLOTCLOSE, and thus can
be modified without affecting any other portion of the code.  A simple
FOR loop can be used for character by character output, but will be
much slower.  If the output rate is limited by a printer, this will not
matter, but for diskfile output will be a nuisance.  Printers with other
formats (interleaved, etc) may require some local data manipulation
and/or combination of adjacent strips.


Virtual Memory
==============

The system uses a virtual memory scheme for the bit map, thus allowing
execution on systems with limited data segments (CPM, HP3000, most
8086/MsDos compilers).  This uses the random file access procedures
of PascalP ('update', 'reposition') and the non-aborting 'allocate' (which
is identical to 'new', except returns NIL in place of aborting when memory
is not available).  To use 'new', adjust the constant 'maxloaded' downwards
until the program stops aborting.   Any adjustments to other systems
should be confined to 'getstrip', 'keepstrip', 'plotopen', (and possibly
'plotclose').

On any system, if the pagesize or resolution is increased, sooner or later
the virtual memory will be required, since internal memory is always finite.


References
==========

Much code was adapted from DOTGRAM (1986) (of the PHYLIP suite), by
Felsenstein and Meacham, and ELLIPSE (1985) by C. B. Falconer.  The
methods are expounded in Decision Variables, by Tom Hogan, Dr Dobbs
Journal, May 1985, and Algorithm for Computer Control of Digital
Plotter, IBM Sys. J. 4(1):25-30, 1965.  The fundamental algorithm is
known as Bresenhams algorithm.


C.B. Falconer 87/02/02
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