YOUR OFFICIAL RASPBERRY PI MAGAZINE

INTERACTIVE PIXEL PET
Tutorial
Fig 2 Two very
simple frames
can give you
enough variation
to create an
animation, even
if the difference
is a few pixels!
Simply select the colour you wish to use from the
grid with your mouse pointer, and then select the
circle in the grid to change it to that colour.
Alternatively, you may wish to draw your picture
out on squared paper with coloured pencils. You'll
need two pet designs, with the second preferably
very similar to the first, so that we can animate your
pet. In Fig 2 above, you can see that our two images
are almost identical to each other, but the feet are
in a different place.
Later, when you code your animation, you will
create the illusion that the pet is walking.
Labelling each pixel
Think of a letter from the alphabet to represent each
colour in your pixel pet image, for example, w for
white or r for red. If using squared paper for your
design, you can write the letters on top – see Fig 3 on
the next page. Note that e stands for empty.
If you're using the 8x8GridDraw editor, then you
can write out your squares on paper, representing
each colour with a letter and separating them with a
comma. Alternatively, you could type them into a text
editor like Leafpad, which you can find by clicking on
Menu, Accessories, and Text Editor. You’ll end up
with something that looks like this:
make up the LED matrix on the Sense HAT. Repeat
this step for your second pet design, so that you
end up with two grids of letters. Can you think of
any problems that might arise when only using one
letter to label different colours? How might you
solve this issue?
When you code your
animation, you will create
the illusion of walking
Code your pet
Now that you have your designs represented as
letters in a grid or array, you can start to code them
in Python. Click on Menu then Programming,
followed by Python 3. This will open the Python 3
shell window. Next, click on File and New File to open
an empty text editor window. Save this empty file
as space-pet.py.
First, you'll need to import all the modules and
libraries required for this project in your code,
by typing:
e, e, e, e, e, e, e, e,
p, e, e, e, e, e, e, e,
e, p, e, e, p, e, p, e,
e, p, g, g, p, y, y, e,
e, g, g, g, y, w, y, g,
e, g, g, g, g, y, y, e,
e, g, e, g, e, g, e, e,
e, e, e, e, e, e, e, e
You’ll notice that we have eight rows and eight
columns of letters, each separated by a comma, to
from sense_hat import SenseHat
import time
Underneath that, type:
sense = SenseHat()
Note that capital letters, full stops, and commas are
very important in Python. Your code might not work
if you don't include these. Next, create a variable for
each colour label in your pet design, like this…
raspberrypi.org/magpi January 2016 63