Last week, we developed a rough design for the following specification:

• Each balloon is a different color.
• No aquarium; paint entire window blue to represent the sky.
• All balloons start at same starting point, somewhere in the lower-left corner of the screen.
• Every balloon rises to a randomly chosen altitude. Then it moves right towards the finish line. In each move it either rises between 4 and 6 units (randomly chosen) or moves right between 3 and 5 units.
• The 1st balloon to cross the finish line wins. If more than one balloon crosses in the same simulation step, there is a tie.

We identified two classes that would be useful in addition to the main function -- Balloon and Display -- and identified the data and behavior for which each should be responsible. The Lab Entrance Assignment for this lab was to write up a draft balloon.h file for me to review.

Constructing Colorful Balloons

• Create a new folder for the Balloon Race Folder. Make a copy of the Aquarium project file (probably in your "Graphics Lab" folder) to put in the Balloon Race Folder. You may also want to copy your display.cpp file (and possibly main.cpp) from that folder and display.h and the AquaFish and RandGen files from the GRAquarium folder on Dragon.

• Be sure to declare and define the Balloon constructor and its Color function. Comment out other member functions in the header file until you are ready to implement them. The constructor will definitely need the starting location as a parameter; you should also pass in the color or plan to choose it randomly in the constructor. You may wish to have other parameters for the constructor as well. (You will also need a default constructor so that you can create an apvector of balloons.)

  Although we used strings to represent Fish colors, use the CMU Graphics Library^* color class (note the lack of capitalization) for the private data member of Balloon, the Color function return type, and the parameter to the constructor (if you pass the color to the constructor). To construct a random color (either in main or the Balloon constructor), you will have something like one of the following:

        color randomColor(r.RandInt(255), r.RandInt(255), r.RandInt(255));
    or  myColor = color(r.RandInt(255), r.RandInt(255), r.RandInt(255));
  

  You will need to include the CMU graphics header file (see display.h or display.cpp) to be able to use the color class.

• Write a simple main function that will construct a single (colorful) balloon. You can't display it yet, because we haven't implemented the Display member functions, but you should still compile and run it to catch any syntax errors.

Displaying a Balloon.

• Edit the Display header file to make the member function and data member names meaningful in a Balloon Race context. You may wish to comment out all the member functions except the constructor and the function to draw a single balloon.

• Implement the function to display a single balloon. Assume for now that the balloon is at location (0, 0). Experiment to decide how to draw a balloon, and what size it should be. You may choose to draw a circle (which should be the color of the balloon), then draw two lines to a small rectangle (which could always be the same color). Or you may apply your own creativity to develop a picture of a single balloon.

  HINT: You may wish to use the DrawCircle or DrawEllipse functions. To draw a circle, you provide the x- and y-coordinates of the center of the circle, the radius, and whether you want it filled, framewire, etc. To draw an ellipse, you provide the same information you would for a rectangle (upper-left and lower-right corners), but it draws an ellipse in that rectangle.

  void DrawCircle (int centerX, int centerY, int radius, FILLED);
  void DrawEllipse (int leftWall, int topWall, int rightWall, int bottomWall, FILLED);

• Update your main program to display the balloon after you construct it, in order to "test" your drawing.

• Figure out how to draw a balloon at any given (x, y) location. Assume that x and y are pixel locations, so you will not need to use scaling factors as we did in the AquaFish program.

• Make sure that the starting location for the balloon in your main program is something other than (0, 0) to test your completed display function. Divide the dimensions of the graphics window by the appropriate scaling factors to determine maximum values for your starting x and y coordinates.

• Implement the function to paint the entire sky blue. Add a call to this function in your main program and test it.

Save your modifications.

• Do not print your program yet. You will not hand in anything as part of this lab, just the completed project as your programming project next week.

  Do remember to save your code, though. Remove the object code from the project, and copy the Histogram Lab folder from the Temp folder to your floppy disk. You should then remove the folder from the Temp folder on the C: drive.

The Balloon Race

If you have extra time, continue to develop the other Balloon methods and update your main function to implement the Balloon Race programming project (due next week at the beginning of lab).

^*The CMU Graphics Library was created by the Carnegie Mellon University School of Computer Science and is used in their introductory programming courses. It is available from Mark Stehlik's Advanced Placement page.