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					figure.hlp page 1:9




Version 2, January 1975

Author: Ake Blomberg, National Defence Research Institute
	Stockholm, Sweden

					page 2
The Tektronix 4012 terminal is equipped with a screen
divided into 1024*760 raster points, between which an
electron beam can draw visible lines. 
1 cm = 48 or 49 raster points approximately.

The raster points are addressed modulo 1024 in both di-
rections  and the addresses should be transformed to 
characters before transmission to the terminal.

The quality and sharpness of lines may vary over the
screen, but should be adjustable.
Further details concerning the terminal's mode of ope-
ration can be found in the terminal's Users Guide.

The user of a hard copy unit should notice that the
size and shape may be altered on the copy.

Special tty settings may cause failure (e. g. crlf).

The following files contain the code described:

source code:
figure.sim, graph.sim, getch.sim, getch.mac,
rubout.sim, rubout.mac, cosys.sim, cosysf.sim,
macsim.mac, all contained in DTA:DEQZ34 figsim.src.

object code is contained in the library sys:libsim.
(use the search switch when loading, but notice the automatic
 search performed by the Simula RTS).
attribute files are found in sys:libsim.atr.
					page 3
Plotting is achieved in two ways, by using class
figure or class graphics.

Using class figure, one generates figure objects
which in principle consist of text objects each
containing a sequence of plotting commands. The
figure objects can then be plotted, saved on ex-
ternal disk files, reread or transformed.

Class graphics is rather used as a block prefix,
thus allowing the user to operate directly on the
screen, without constructing figure objects.
Class graphics also contains a procedure for con-
trolling the terminals geometric cursor.

Neither class is highly optimized or far developed.
The user should not find it difficult to include
his own special procedures according to diffe-
rent requirements and some optimization may be
achieved by rewriting some procedures in assembly
language or perhaps by turning the security swit-
ches off at compile time.

When drawing lines the terminal is in geometric
mode and cannot produce characters before it is 
reset to alpha-numeric mode. Therefore, runtime
errors during drawing may result in non readable
error messages.

To save some time at execution, the addresses are
not calculated modulo 1024 and therefore runtime
errors may result when attempt is made to plot 
outside screen (usually ZYQ006 error message).
					page 4
Class graphics description

Contained in the files graph.*. Class graphics
requires external character procedure getch,
which accepts single characters from the termi-
nal. Getch is coded in Macro-10 language and
uses macro instructions from the universal
macsim when compiled. Observe that a dummy pro-
cedure in simula is required to generate the
attribute file.

To use graphics, one has to declare

external class graphics=graph;
external character procedure getch;
graphics begin ...

Then the following procedures are available:

move(i,j);	(integer i,j) moves the turned
		off electron beam to the point 
		(i,j) on the screen. Also sets
		geometric mode.

draw(i,j);	draws a line from the previous
		position to (i,j). Assumes that
		geometric mode has been set.

reset_tty;	resets alpha-numeric mode. To
		be used before writing.

getpos(i,j);    gets current location of beam

cursor(c,i,j);	(character c, integer i,j) calls
		the geometric cursor. When push-
		ing a character key this charac-
		ter is sent to c and the address
		of the cursor to (i,j).
					page 5
Class figure description.

Contained in the files figure.*. Written
entirely in the Simula language.

Should be declared as follows, for the case
of two figure objects:

external class figure;
ref(figure) a,b;
a:-new figure; b:-new figure;

Then the following operations are available
on a and b:

a.origin(ox,oy);  (real ox,oy) sets origin to
		  (ox,oy) measured in raster
		  points. (0,0) is default.

a.scale(sx,sy);   (real sx,sy) sets scale mul-
		  tipliers to (sx,sy) in x- and
		  y-direction. Scale does not
		  affect origin. Default (1,1).

a.checkon;	  turns the sizecheck on.
		  When the sizecheck is on, the
		  numbers a.xmin, a.xmax, a,ymin
		  a.ymax are calculated in each
		  following plotstep, measuring
		  the size of a in raster points.
		  Boolean procedure a.on_screen
		  returns true if a is contained
		  within the screen.
		  Checkoff is default.
					page 6
a.moveto(x,y);	(real x,y) moves the turned off
		electron beam to the raster point

a.drawto(x,y);	(real x,y) draws a lline to the
		raster point (ox+sx*x,oy+sy*y)

a.plot;		plots a on the screen. Does not
		affect the contents of a.

a.addfig(b);	(ref(figure) b) concatenates the
		figure b to a. Does not affect the
		contents of b.

a.write(s);	(text s, text constant allowed)
		writes s into a.

a.savefig(s);	(text s, text constant allowed)
		writes the contents of a onto a
		disk file named s. Does not affect
		the contents of a.
a.getfig(s);	(text s, text constant allowed)
		reads a disk file named s previously
		written by savefig, into a. Old
		contents of a destroyed.

a.recompute;	unpacks the plot characters of a
		into real numbers and transforms
		them again with the current ori-
		gin and scale. Can be used to chan-
		ge origin or scale. Contains the
		decoding procedure for figure ob-
		jects and can be used as a model
		for other tranformations.

					page 7
The formulas for transformation between coordi-
nates and plot characters are contained in the
procedures trans_to_plotchar and recompute. The
plot characters are contained in the text object
T and the integer variable CC is a character
count for T. Most of the time CC = T.pos-1.

The user is recommended not to alter T, T.pos
or CC, which are qualified candidates for the
Hidden declaration, if anytime included in the
Simula language.

To erase the screen the procedure rubout can be
used. It is coded in Macro-10, but does not re-
quire macsim when compiled.

To make a pause in the execution after having
drawn a figure one can write setpos(0); inimage;
Nothing will happen before the Return key is

Ref(figure) procedure cosys can be used to con-
struct coordinate systems with tic marks. The
source code contains description.

Ref(figure) procedure cosysfor(xmin,xmax,ymin,ymax)
constructs a coordinate system suitable for the
given extremes.

It should be possible to use the principles of Figure
for other graphic equipments than the Tektronix
4010 series.
					page 8
Example of the use of class graphics

The procedure cursor can be used to transmit
commands to a program without having the com-
mands echoed on the screen and together with
geometric data.
The following program will allow the user to 
draw straight line figures by adjusting the
geometric cursor and sending a one character
command for moving, drawing or erasing.
It is not difficult to extend the program to
simulate the tools of Euclidean geometry, viz.
ungraded ruler and compasses.

Begin external procedure rubout;
External character procedure getch;
External class Graphics;
Character c; integer x,y;
Graphics begin rubout;
	 while c \= 's' do
	    if c='m' then move(x,y)
	    else if c='d' then draw(x,y)
	    else if c='r' then rubout;

					page 9
Examples of the use of class figure

Let f denote an already constructed figure.

1. Translate f with (tx,ty) raster points, kee-
   ping the scale:
   f.origin(tx,ty); f.scale(1,1); f.recompute;

2. Change the scale with the factors (sx,sy)
   with fixed origin:
   f.origin(ox*(1-sx),oy*(1-sy)); f.recompute;

3. Example of a program that will draw six con-
   centric ellipses:

Begin external class figure;  ref(figure) f;
Real w, dw;  Integer i;
f:-new figure; 
f.origin(510,380); f.scale(240,240); f.moveto(1,0);
w:=0; dw:=3.1415926/50;
for i:=1 step 1 until 100 do
begin w:=w+dw; f.drawto(cos(w),sin(w)); end;
for i:=1 step 1 until 5 do
    f.scale(0.9,0.6); f.origin(510*0.1, 380*0.4);
    f.recompute; f.plot;

--------------------End of Figure.hlp-----------------