Quick On The Draw
THE BBC Micro has some excellent graphic commands - MOVE, DRAW,
PLOT, GCOL, etc — built into its Basic. But they are rather tedious
to use for anything but the simplest of pictures.
It is better to use (or write) a general purpose drawing program
which employs the cursor keys to move about the screen and draw
or indicate the location of previously defined objects.
Movement may also be made somewhat easier on a Model B by using
the analogue port, ADVAL command and joysticks to replace the
cursor keys.
The two systems reviewed here take us a step further in putting
pictorial information into the computer. Both employ graphic tablets
and a control program and allow the user to trace around actual
pictures with a drawing arm.
These devices send X and Y coordinates of their position on
the board, via the analogue port and appropriate programming,
to the screen display (see Mike Cook's article on building a drawing
arm in The Micro User, June 1983).
Both systems were tested on a 32k BBC Micro Model B with OS
1.2 and Basic II. So, how do the two compare with each other?
Beebplotter Watford Electronics
THIS is supplied as a graphics tablet manufactured by Robot
Developments of Hull, software on cassette and a manual.
The tablet is a sturdy transparent sheet of smoked Perspex measuring
48x40cm with a grid marked drawing area approximately 32x23cm.
It has an advantage over the Grafpad in that it can be placed
over thick books to trace maps and diagrams and the source picture
can be kept still without having to resort to sticking it down.
The tracing arm is the two piece potentiometer type and is well
constructed in tough plastic.
The system plugs into the micro's analogue port via a 15 way
D connector (provided) attached to a rather short (95cm) lead,
which rather restricts the position of the tablet in use.
One thoughtful feature is the provision of a command summary
on the tablet itself, as the list given on screen by the intro
program is soon forgotten.
The software consists of two Basic programs - one giving instructions
and setting up the grid, and the main program - two runplot routines,
and five demonstration files.
Setting up time, including loading the programs and calibrating
the grid, took me only two and a half minutes.
You are then asked to select a mode (0, 1, 2, 4 or 5) and whether
a previously saved picture is to be loaded.
The facilities available are described in Table I and are selected
by pressing the appropriate key. The space bar is used to indicate
entry of a digitised point.
All this key pressing caused much distraction when tracing a
drawing from the tablet.
In use, the LINE, RECTANGLE and CIRCLE options are very good
as the potential position and shape of a figure can be visualised
on screen before being fixed. In addition, a picture component
can be removed in EDIT mode.
The MOVE/REDRAW feature is also useful as whole shapes can be
duplicated in another position on the screen without having to
redraw them manually (Figure IIIa). Text can also be added anywhere
on the picture using the PRINT AT ... option.
One of the most useful features is the FOLLOW option which allows
the user to trace complex shapes. Rather disappointingly this
is spoilt by stiffness of the drawing arm, making it difficult
to draw smooth lines even after practice
The cursor spot on the screen has a slight tendency to wander,
requiring the space key to be hit at exactly the right time for
precision.
Unfortunately the software is not completely idiot or bug proof
on two of the options. Injudicious use of the infill command -
for example if a shape is not completely closed or if used on
top of an already filled area - caused me irreversible program
crashes.
Also when altering colours - both foreground and background
may be altered - the command instruction itself changed colour
and sometimes became invisible, making remedies difficult.
It is also a good idea to note the colours and mode of a drawing
when saving, as the latter cannot be altered during a run. Surprisingly,
crashing the program is also not uncommon when loading the demonstration
files.
A printout option is provided in the command table, though the
user is expected to incorporate a screen dump facility into the
empty procedure in the main program.
This was fairly easy to do and worked well with both an Epson
dot matrix and an Olivetti ink jet printer.
The plotter programs, and saving or loading of picture files,
worked on either tape or disc systems without any modifications.
Grafpad Micrex
THIS package also consists of a graphic tablet - in this case
called a graphic digitiser - a software cassette and a manual.
The tablet is a solid laminated board measuring 51x46cm and
is finished in BBC cream (see picture). The drawing area is slightly
squarer and larger (29x28cm) than on the Beebplotter.
The drawing arm, which is also of the two piece potentiometer
type constructed in metal and plastic, seems less sturdy than
the Beebplotter, though it has a locking pin for when not being
used.
It does, however, have the big advantage of being much easier
and smoother to use, and, combined with the fact that the screen
cursor doesn't wander, it seems much more accurate.
A Draw button is also provided on the board to indicate the
start and end of a digitising action - an improvement on the Beebplotter's
"press the space bar".
Unfortunately, the connecting lead, terminated by the analogue
D plug, is even shorter (80cm) than on the Beebplotter, causing
difficulties in board positioning.
The software provided is in Basic and includes a loader/instruction
program, a main program, three data files and a redraw routine.
On running the loader program I experienced a feeling of deja
vu as the standard Clare's Grafkey/Grafdisk/ Grafstik instructions
appeared.
The features available are shown in Table I and are operated
by the function keys for which a tear-off crib sheet is provided
to fit under the BBC's plastic strip.
Function key 9 acts as a shift key to obtain more options, but
is a little too close to the Break key for comfort.
All the features of Beebplotter are present, except for MOVE
and EDIT -a pity as these can prove particularly useful. There
are, however, some additional routines in Grafpad — TRIANGLE,
RUBBER-BANDING and superimpose GRID.
Perhaps the most significant of these is rubber-banding, in
which the user can indicate up to four points (for example, the
base of a pyramid) and then move the plotter around to "pull
out" the apex and attached vertices (Figure Ib).
Selection of colours - 16, including flashing, are available
- is easier than Beebplotter as a palette is displayed on screen
and the required colour digitised. However, unlike Beebplotter,
only foreground colours are available.
One advantage of Grafpad is that the mode (0, 1, 2, 4 or 5)
can be changed without losing the current picture.
Perhaps the biggest joy (and disappointment) is the PAINT mode,
operated like the FOLLOW mode of Beebplotter. This allows fairly
accurate tracing of diagrams placed on the tablet or can be used
for doodling.
It is also possible to vary the thickness of the brush and therefore
use it to shade in areas making intricate and pretty pictures.
The disappointing part is that following all that effort, the
painted portions of the pictures cannot be redrawn following a
screen clear, nor can they be saved on tape.
The complete screen SAVE option is only available on the disc
version of the program otherwise saving and loading files is straightforward
and works well, though there is no facility to provide separate
filenames for pictures.
All were called DATA. Thus searching for a particular picture
was tedious.
No printout or screen-dump facility is provided - a big minus
for any computer aided design work — and it is difficult to add
one's own print routine owing to Clare's extensive software protection.
Similarly, I found it difficult to modify the tape version to
work on disc systems. But a separate redraw routine is provided
to enable users to incorporate pictures drawn with the Grafpad
into their own programs.
CONCLUSION
OVERALL, both systems performed reasonably well, though in a
limited fashion. Both are well constructed and though Beebplotter
was easier to set up and use, perseverance with the Grafpad paid
its rewards eventually with more versatile pictures.
In both systems, transfer from graphics tablet to keyboard for
the commands was a nuisance and could probably have been replaced
by a digitisable menu on the tablet.
Disadvantages of the Beebplotter, such as a stiff drawing arm
and occasional program crashes, may be balanced against the advantages
of a transparent baseboard and its MOVE and EDIT facilities.
On the whole, Grafpad's tablet performed well, as did the software
with its extra features.
Its biggest drawback was the inability to save traced (PAINT
mode) drawings, one of the main reasons for using a graphic tablet
in the first place, and the lack of a printout option.
Both systems should be satisfactory in an educational environment,
especially for reproducing simple geometric shapes and for drawing
pictures to add to one's own programs.
Their tracing facilities are somewhat limited and therefore
they offer only small advantages over other cursor or joystick
drawing programs ... and at a price!
They do, however, introduce the user to some of the excellent
graphic capabilities and high resolution plots of the BBC Micro.
But for more professional computer aided design or technical work
requiring the measure-ment of traced areas, a non-potentio-meter
type digitiser will probably be needed.
Mike Mahon
|
Beebplotter
|
Grafpad
|
|
Facility
|
Key
|
Facility
|
Key
|
|
Line
|
L
|
Line
|
f0
|
|
Rectangle
|
R
|
Triangle
|
f1
|
|
Print at ...
|
P
|
Rectangle
|
f2
|
|
Circle
|
C
|
Write text
|
f3
|
|
Define colours
|
D
|
Circle
|
f4
|
|
Alter colour
|
A
|
Rubber banding
|
f5
|
|
Infill
|
I
|
Colours
|
f6
|
|
Follow
|
F
|
Fill
|
f7
|
|
Move and redraw
|
M
|
Paint
|
f8
|
|
Edit
|
E
|
Brush width
|
,
|
|
Wipe screen
|
W
|
Grid
|
f9 f0
|
|
Save picture
|
S
|
Clear graphics
|
f9 f1
|
|
Load picture
|
ESC
|
Redraw
|
f9 f2
|
|
Memory left
|
@
|
Save picture
|
f9 f3
|
|
Clear data
|
ESC
|
Load picture
|
f9 f4
|
|
Select mode
|
01245
|
Free memory
|
f9 f5
|
|
Printout
|
X
|
Purge
|
f9 f6
|
| |
|
Change mode
|
f9 f7
|
Table I: Facilities and commands available on each system
Figure I: Output from (a) Beebplotter (b) Grafpad
