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General background information

When we finished the previous module, we were missing one critical element needed to write a simple game program: user input . We were also lacking some other tools that would make it possible for us tocreate more interesting 2D arcade-style games including the ability to create on-screen text.

In this module, you will learn how to program for user input with the keyboard and the mouse. You will also learn how to create on-screen text.


The program that I will explain in this module is a simple game in which ten spiders attempt to traverse their web from top to bottom. Two largeladybugs are there to eat them if possible. (See Figure 1 .) The objective of the game is to prevent as many of the spiders as possible from making it tothe bottom of the game window.

Figure 1 shows a reduced view of the game window shortly after the game is started and before any spiders make it to the bottom.

Figure 1 . Reduced view of the game window.

missing image

Spider behavior

The spiders move at different speeds in different directions but generally towards the southeast. If a spider makes it to the bottom, it is counted ashaving crossed the finish line. That spider wraps back up to the top and starts the journey again. If a spider hits the right edge of the window, it wrapsaround to the left edge and continues the journey.

The ladybugs

The movements of the ladybugs are under the control of the player. If the player causes a ladybug to collide with a spider, the spider is eaten andremoved from the spider population.

Using the keyboard

The player can move the ladybugs using either the keyboard or the mouse. Pressing the four arrow keys causes one of the ladybugs to move in thecorresponding directions. Pressing two arrow keys at the same time causes the ladybug to move in a diagonal direction.

Holding down the A key and pressing the arrow keys causes the other ladybug to move.

Using the mouse

Pressing the left mouse button makes it possible to drag a ladybug with the mouse. Pressing the right mouse button makes it possible to drag the otherladybug with the mouse. Pressing both mouse buttons makes it possible to drag both ladybugs with the mouse.

Difficulty level

The game has only one level. I personally find it very difficult to prevent all ten spiders from making it to the bottom using the arrow keys only. On theother hand, it is easy to defeat the spiders by dragging a ladybug with the mouse.

A useful student project

A useful student project would be to upgrade the program to provide varying levels of difficulty. This could be accomplished by changing the speed of the spiders, changing the number of spiders, or a combination ofthe two.

Alternatives to the arrow keys

Another useful student project would be to define alternatives to the arrow keys, such as the keys labeled 4, 8, 6, and 2 on the keypad, or four keys in adiamond pattern on the left side of the keyboard.

Discussion and sample code

As usual, I will break this program down and explain it in fragments. However, I will only explain those portions of the code that are substantiallydifferent from code that I have explained in earlier modules.

Questions & Answers

what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
many many of nanotubes
what is the k.e before it land
what is the function of carbon nanotubes?
I'm interested in nanotube
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
preparation of nanomaterial
Victor Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Xna game studio. OpenStax CNX. Feb 28, 2014 Download for free at https://legacy.cnx.org/content/col11634/1.6
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