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Cowabunga

In this assignment you will use universe to create a simple game. In the game you pilot a UFO and attempt to abduct cows without hitting the ground.

To get started you will need the universe.ss teachpack. This teachpack is preinstalled in DrScheme, so you just need to add it to your language. Do this by selecting "Add Teachpack..." from the "Language" menu and choosing universe.ss from the list on the left.

You will also need the four clipart images found at http://world.cs.brown.edu/1/projects/cowabunga/. You can insert an image into your Scheme code by selecting "Insert Image..." from the "Insert" menu.

Finally, you may want to look through the fully worked-out example of a universe program (Flight Lander) in How to Design Worlds.

The Problem

When you are finished, your game should contain the following:

• A UFO that moves continuously downward from the top of the screen. The user can control the left-right motion of the UFO with the arrow keys.
• If the UFO gets to the side of the screen, it should simply hit a wall (and not be able to fly off the side of the screen).
• Multiple cows moving in both directions along the bottom of the screen.
• The cows should detect collisions with the sides of the screen and with each other and reverse direction when they collide with something.
• If the UFO hits any of the cows, it should change to the red UFO and the game should end.
• If the UFO hits the ground, it should NOT change color and the game should end.

To make the assignment easier, you may want to break it up into simpler stages. We suggest you look at the intermediate stages listed on the same page as the images. That page also has some useful videos to give you an idea of what your game should look like.

Testing

Your test cases will be a major part of your grade on this assignment. Remember, many of your functions have graphical output, which makes them difficult to test. This puts an even greater burden on how well you test your non-graphical functions. We expect to see you sustain this burden.

What to turn in:

• A Scheme file, cowabunga.ss, with code implementing the finished game.