CSci 1301: Lab 6

Due: Friday, November 9th at 11:59pm

What to submit

The lab is done in groups of 2 or 3.

Balloon problem (30 points)

Start with the balloon exercise and implement the world functionality as described below. The "world" is a multitude of randomly generated balloons that start at the botom of the screen and float up. The world state is a list of balloon structures. The structure is already defined in the file:

  
    (define-struct balloon [x y size color])

    ;; example:
    (make-balloon 100 200 2.5 "blue")
  

1. The function balloon-picture that takes a ballon structure and returns the picture of the balloon of the given size and color. It doesn't use the coordinates. the function must work according to the two given check-expects.
2. Add at least one check-expect for the function draw-balloons. The function takes a list of balloon structures and returns a scene width-by-height in which all baloons are placed one-by-one on top of the empty scene.
   After you have added the check-expect for an empty list and perhaps more, implement the function accordingly.
   When you run your program, you should see the two starting balloons on the scene. They don't move yet.
3. Write tests for the function move-balloons according to its description. Think of how the balloon positions change on every clock tick, then write the list of balloon structures with the new positions. Note that there is a speed constant defined.
   Once you have written the tests, implement the function. You should see the two balloons floating up.
4. Once you get this to work, change the initial state to generate a list of two balloons at the random x poistion at the bottom of the screen with a random size (i.e. the scaling factor) between 0.5 and 1.5 and of a random color that you can get by passing a random number to the color chooser. Watch your new balloons float up.
5. Change your move-balloons function so that when a balloon disappears from the screen, it is removed from the list. You should write a predicate is-visible? that checks if a balloon is still visible on the scene. This feature is very important for writing games: if you don't remove invisible objects, you get too many of them and your game starts slowing down.
   In order to check if it worked, click to exit the program once the balloons are off the screen, and check the world state printed by the program to see if they are still in the list. Study the filtering example in the solutions for making lists to help you implement this feature.
6. Further change the move-balloons function to add a new balloon at the bottom of the screen at a random x coordinate and of a random color and size (use color-chooser, feel free to add more colors) on every clock tick. Add it to the end of the list (the base case for the empty list). Think carefully of what kind of thing the function needs to return (hint - look at the signature!). Important: your check-expects will fail at this point; comment them out or switch to check-random.
7. Change your solution by adding an additional feature of your own idea and design (you may change your solution to the previous question; comment out the old code, but don't delete it). You can add features such as: adding a new balloon with some probability rather than on every clock tick (to avoid filling up the screen too quickly). You can add "wind" that makes balloons shift horizontally, in addition to vertically. You can have a balloon pop at random, or when it hits a tree branch.
   Your world state must still be a list of balloons.
   Especially interesting solutions may get an extra credit.
   Clearly document the features that you are adding. Make sure that your functions have good names and signatures and descriptions.

How to submit

Name your file with the combination of your last names, no spaces, followed by the word "Lab" and the lab number. For instance, if your last names are Smith and Lee, the file name should be SmithLeeLab6.rkt If there are others in the class with the same name as yours, you your initial in addition to your last name: MSmithJLeeLab6.rkt

At least one person in the group must submit it via canvas as a file upload (make sure it's that .rkt file). Make a comment indicating who you worked with. The other person (or people) in the group may submit the same file and also indicate who was in the group or just make a comment listing all your group members (note: if you don't submit a note listing your group members, your work may not be counted, even if your group partners list you as the group member).

CSci 1301 course web site.