PC Logo

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PC Logo How to
First of all lets look at the windows you are
going to use. At the top you have a toolbar,
with all your various tools you can use when
customising your procedures. Under that you have
the large window, called Graphics where you can
see what effect your commands are having.
Underneath that you have the Listener where you
actually give your commands. Talking of
commands, lets have a look at a few of the more
basic ones, and get your turtle doing something.
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Commands
The very first, most used commands you will need
are incredibly simple. FD X commands your
turtle to go forwards by value X RT X
commands your turtle to turn to the right by X
degrees. Lets do something simple, how about a
square. Type fd 50 and then rt 90 four times.
Your listener should look like this after you
have finished.
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Commands
As you can see, this method, while hard to get
wrong, takes quite a lot of typing to get any
sort of shape, imagine trying to draw a circle
like this. There is a far easier way to do this
however. Type CS to clear your screen, so we can
start on something slightly more advanced. Now,
lets make a circle. Unless you want your hands
to fall off though, we are going to have to find
a slightly faster way to do this. Lets make a
procedure.
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Procedures
Now, lets decide what to call your procedure.
Were going to draw a circle, so lets call our
procedure circle. Type edit circle This
should open up a new window, like this. It
should be titled Circle, and start with TO
CIRCLE. Now, lets make it do something shall we.
We want it to draw a circle, without having to
do lots of typing. The answer to this is the
Repeat command.
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Repeat
As the name suggests, the repeat command repeats
whatever you tell it to. What we are going to do
is tell it to draw a circle. So, type repeat
360 fd 1 rt 1 This tells the procedure to
repeat 360 times the commands fd 1 then rt 1. So
the repeat command can be summed up like
this repeat X Y Which means repeat command
Y, X times. Press F2 to leave the editor.
You should see circle defined in your listener.
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Our Procedure
Now, lets test our procedure. Type circle into
your listener, and press enter. You should see
this. To vary the size of your circle, change
how much the turtle moved in the FD command in
your procedure. However, that takes time, and
you arent sure of what it will look like until
you have done it. Lets speed this up shall we.
Lets use variables.
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Variables
A variable is something we can change in the
procedure, without having to edit it every time.
Lets call our variable X. So, open your
procedure with edit circle, and lets change it
around a bit. Where it says, TO CIRCLE, change
it so it says TO CIRCLE X. This means that when
you type circle, you must also give a value of X.
Now, change your procedure, so is says repeat
360 fd X rt 1 Now you can vary how far the
turtle moves every repeat. Press F2, and try
typing circle 2. You should see this.
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Variables
Now, with variables, a whole new world of
possibilities has opened up for us. If we put
our minds to it we could make any shape we could
ever imagine. You can have as many variables as
you like in a procedure, for example you could
have a procedure called SHAPE X Y Z Or any
other combination. Now lets make a procedure
that will make a shape with a number of sides X
and a side length Y As you may know, the
exterior angle of a shape is 360/No. of sides.
So our procedure would look something like this.
First, lets call it POLYGON.
90
120
360 4
360 3
30
360 12
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POLYGON
Now, type edit POLYGON into your listener. We
need the top to say TO POLYGON X Y Then,
type repeat X fd Y rt 360/X This lets us
set the number of sides, and the length of each
side. Lets give it a go shall we? Lets start
with a square, of side length 50, and of course
with 4 sides. You should get this, if not, go
back and check for any typo's in your
procedure. Now, one more thing before we get
onto some really hard stuff.
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Circles (again)
With all the circles weve drawn, we have set the
circumference, not the radius. Lets see if we
can try and make a procedure where we set the
radius, of the circle, and the program works out
the rest. So first, were going to need a
variable, X, and the value of pi. Logo takes
this value to 3.14, which is close enough for our
means. Lets call our procedure CircleR meaning
it is a circle where you set the radius. So,
type edit circler in your listener, and type
this Give the procedure a variable X Tell it to
repeat 360 times forward 2pX then right turn
by 1. Remember, to multiply use not x.
Circumference
D
R
Circumference pR2 pD
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Circles
So, with all that done, does your procedure look
like this TO CIRCLER X REPEAT 360 FD ((PI
2 X) / 360) RT 1 END If so well done,
you have made a procedure where the value X is
the radius, and the circumference is done by
Logo. Try is out, and you should get this, set
X to 50. This is useful for making a drawing
significantly more precise. Now, lets move onto
something even better spirals!
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Spirals
Weve made all sorts of shapes, but they all have
one thing in common they start and end at the
same place. What about a shape that starts at
one place, and ends in another, like a spiral.
Lets start with something basic, like a square
spiral. This involves quite a jump in procedure
complexity so make sure you type everything
correctly first time! Lets call it Sqspiral
square spiral. Type edit sqspiral into your
listener, and give it 2 variables, X and
Y. First, were going to need to stop our spiral
growing out of control, so type IF X gt 200
stop Then just tell it to go forwards by X and
right by Y. Then and this is the important
bit, type sqspiral X 1 Y This is the bit that
makes it expand into a spiral. Go to next slide
for the finished procedure. You will notice that
here the procedure calls itself, otherwise you
would have to type it every time X changed! How
tiring!
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SQspiral
Does your procedure look like this TO SQSPIRAL
X Y IF X gt 200 STOP FD X RT
Y SQSPIRAL X 1 Y END If so, well done,
and lets give it a go. Press F2 to save it, and
then type sqspiral 0 90 into your listener. Does
it look like this? With this procedure you can
make a spiral with any number of sides, with
right angles, or with triangles, or anything you
can imagine, within some limits. This procedure
will not produce a circular spiral, so thats
what were going to do next.
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Circular Spiral
Now, lets start on our circular spiral. We need
to give it a name first. Lets call is Cspiral.
To get it to work, we need to work a few things
out first. We need to work out, for example, the
distance between two layers of the spiral, and
make this distance constant throughout the
spiral. This instantly means that we are going
to have an X Y part in there somewhere. Now
we need to find an appropriate value for Y. To
work this out we need another constant, Z. So,
if Z is the distance between two layers, say
0.1, and Y is what we do to X, then we need to
increase X by 0.1 every 360 of rotation. The
answer is now clear. Y 0.1/360. So now we
know what our procedure is going to look like.
Try and put it together, and see if it works.
Remember all the limiters to stop it expanding
out of control! Go to the next slide to see my
solution to this problem.
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Cspiral
Does your procedure look something like
this? Note The only reason we have a variable is
so that we can change it within the procedure
itself. TO CSPIRAL X FD X RT 1 IF X
gt 2 STOP CSPIRAL X (0.10 /
360) END And, does the spiral it produces look
something like this? (set X as 0.1)
If not, give it another go, or just copy out the
procedure I used.
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An Animation
That was fun but it is still quite limited.
Lets move onto something a bit more fun. Lets
make an animation. This will require a few
steps, but well get there! First, I am going to
explain why I have designed it like I have, and
then Ill set you to putting it all together for
yourself. The animation I have made is very
simple, but requires 4 different procedures to
work. This is because when I was putting it
together I did it step by step, to make sure that
everything worked. This has the added bonus of
slowing the animation down enough that it doesnt
hurt your eyes when you play it. You can
amalgamate all the procedures into one if you so
wish, but I dont think you will like the result,
and it gives you quite a headache after a while.
So, lets begin!
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Our Animation
Our first procedure were going to make is called
TA. Its very simple, and it goes RT 30 FD
50 REPEAT 2 RT 120 FD 50 Then we have TA2,
which goes TA REPEAT 2 FD 50 LT 120 FD
50 You will notice that this procedure draws on
a previous procedure. Now for TA3, and it
goes TA2 PE TA2 PD
PE means pen erase which causes the pen to
erase any lines it touches. PD is pen draw, the
default mode. And now, for the final one, called
ANI. ANI goes REPEAT 100000 TA4 RT 1 Give it
a go, put them all together, then sit back and
watch. It is very basic, but all my attempts to
make a more advanced animation have been met with
failure. Perhaps you will have more luck? One
more thing. This animation will never stop, and
if you leave it too long, it crashes your
computer. To stop it, press this icon (the one
on the right)
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If all Goes to Plan
If all goes to plan, you should see this on your
screen (click to start and stop when viewing as
slide show.)
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I hope this slide show has helped you, as much as
it helped me when I was making it!