Powerpoint slides on programing/turtle graphics.

Art 321 Lecture 7
Dr. J. Parker
• In order to ‘make things happen’ on a
computer, you really have to program it.
• Programming is not hard and does not
require advanced math skills. It does
require that you understand how limited a
computer really is, and know how to use a
particular language to speak to it.
• There are many ways to program a
computer. Ones uses a ‘drag and
drop’ interface where you click and
drag icons into a sequence.
Another is to use a scripting
language, which is a highly structured
way of giving a computer instructions
on how to do something.
Computers do not think. (want to discuss this?)
They do precisely what you tell them to do.
If a computer does something incorrectly, it is
caused by either a flaw in the electronics or my
a mistake in the program it was given.
Mostly the latter.
HTML is a simple programming language, in a
sense. It describes how a computer should
display a document.
We will look at one of the simplest ways to
program a computer – using ‘turtle graphics’
and Logo.
We are going to use a drop and drop coding
system created by Google, called blockly.
The ‘turtle graphics’ concept has a pen (carried
by a turtle, one supposes) move along a paper.
One can go forward, back, turn left and right,
Lift and drop the pen, change colour, and so on.
We select an action using the mouse and place it
in the window, then click on ‘run program’.
The Abstract Explanation
A variable is a name (IE a symbol) that
represents some value, usually a numeric value.
The name is often indicative of the nature of
the value – so the variable score represents a
value that is also called a “score” in English. This
is a coincidence; the game score could just as
easily be kept in a variable called “fred”.
The Engineering Explanation
The variable is another name for the address in
memory where the value is kept.
The programming language takes the name
that it sees and replaces it with a memory
So score = 12 becomes memory[10020] = 12
Where 10020 is the address of score.
The Common Sense Explanation
A variable is a place to put something; it’s the
name of that place.
What can we do with variables?
We can save things for later.
We can add to them, accumulate values. EG
- How many enemies have we shot?
- How much fuel do we have left?
- Where is my ‘ball’ object?
We can test it against sentinal/target values.
- Am I out of fuel (is fuel = 0)?
- Am I near to a water hole (distance < 20)?
Draw a set of lines
Draw a square.
Draw a square.
Draw a triangle
Draw a triangle
Draw a collection of triangles
Draw a collection of triangles
Results are often surprising
Random positions …
• Repeat many times – select a random
place each time from which to begin.
Details of the ‘loop’
Concept of ‘procedure’
‘a bunch of things
you want to do
that has a name’.
Here, ‘triangle’ is
a procedure.
Now ‘reposition’
is a procedure
It places the
turtle at a new
random point.
The new program
draws a triangle
and then
repositions, 100
Change colors – RGB values can be set.
1. Draw a "+" figure 150 units high by 150 units wide.
2. Draw the letter 'W'. (Bonus marks: draw the word "WHY"
3. draw 5 parallel horizontal lines 400 units long separated by 25 units.
4. Use turtle graphics to draw a sequence of squares (100 units per side)
that have a common lower left corner, but are each drawn at a
different angle. There should be at least 10 squares in the sequence.
5. Draw a set of 9 squares in a 3x3 arrangement. Draw one in each of the
colours: black, yellow, green, red, blue, purple, grey, orange, and a
colour of your choosing.
6. Draw a circle.
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