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through leaf5, and will call a procedure to draw a flower for each costume.
Since we have a single sprite, we only need one copy of the drawing code
(not the five duplicate scripts we had in our first version). This makes the
program smaller and the code easier to understand. When the sprite in
this application receives the Draw message, it executes the script shown in
Figure 4-9.

Set the x-coordinate and the costume for
drawing the first flower.
We need to draw five flowers.
Set the y-coordinate of the flower we are
about to draw.
Call the drawing procedure.

Prepare for drawing the next flower.

Figure 4-9: When the sprite receives the Draw message, it calls DrawFlower
five times (in a loop) to draw five flowers .

The script sets the x-coordinate and the costume for drawing the first
flower and then enters a loop to draw five flowers. On each pass, the loop
sets the y-coordinate for the flower and calls DrawFlower by broadcasting a
message to itself. This call halts the script’s execution until DrawFlower is
done. When this happens, the Draw script resumes execution, adjusting the
x-coordinate and changing the costume in preparation for drawing the
next flower.

n o t e You can name a procedure anything you like, but I recommend selecting a name that
reflects that procedure’s purpose. This is especially helpful when you revisit a program
that you wrote months ago. For example, if you want to show players how many points
they have in a game, you might create a procedure named ShowScore. Naming this
procedure Mary or Alfred certainly won’t remind you (or anyone else reading your pro-
gram) what the procedure does.

The DrawFlower procedure is shown in Figure 4-10. It sets random val-
ues for the color effect, brightness, and sprite size before stamping rotated
versions of the current costume to draw a flower.
While the first version of the program contained five sprites and five
repeated scripts, the second version achieves the same result using a single
sprite that calls one procedure for drawing all five flowers. Open Flowers.sb2
and Flowers2.sb2 in two tabs of your browser and compare them. Isn’t the new
version much simpler to follow? Using procedures lets you make smaller pro-
grams that are easier to understand and maintain. This will become more
beneficial as you write programs to perform more complex tasks.

74 Chapter 4
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