Lab 3: Loops and Lists

Introduction

The goal of this lab is to get more practice working with lists and nested loops. This lab will also help you to get started thinking about PP #1: Joust!. You may be able to use the code from this lab directly in your project. If not, it will at least give you some helpful ideas. If you finish early you should read through PP1 and start thinking about your design for the programming project. Make sure to organize your code sensibly, include comments, and select meaningful variable names. See the Alice Documentation and Coding Standards Guide for specific suggestions.

Exercises

Joust Warm-Up: Bouncing Jousters
One of the difficult aspects of the joust project is handling the collisions between the jousters and the spherical obstacles. Since there are multiple obstacles as well as multiple jousters, keeping track of all of the possible ways that a jouster and obstacle might interact could get complicated. We want to avoid code that looks like the following:
```
 
if jouster1 collides with obstacle1
    handle collision between jouster1 and obstacle1

if jouster1 collides with obstacle2
    handle collision between jouster1 and obstacle2

...
```
This kind of repetition can be avoided if we maintain a list of jousters and a list of obstacles. These lists will allow us to check for collisions between each possible match-up of jouster and collider by using a nested "for all in order" or "for all together" loop. The outer loop will iterate through the set of obstacles and the inner loop will iterate through the set of jousters.

A second challenge is figuring out how to handle collisions once they are detected. A good way to deal with this is to write a "bounce" method that instantly moves any object that tries to move inside a sphere away from the sphere. In order to make a realistic collision animation, I suggest using the "move away from" method with a very short distance (say .1 meters) and a duration of 0.

You can get started by adding a single sphere and a single jouster to an otherwise empty world. Then write and test your bounce method. You'll need to make this a world level method that takes the sphere and the jouster as parameters. (If you try to make it a class level method of the sphere, you won't be able to use it inside of a list. When iterating through a list, all items are treated as generic objects, so class level methods of the list items are not available.) Your bounce method should make use of a function to determine whether or not the jouster needs to be bounced: a jouster should only be moved if it comes too close to the sphere. You can test your bounce method by adding an event to the world that allows you to move the jouster with the mouse or the keyboard. For the final version of your joust game, you will want all of the objects lined up in a plane. Don't worry about that at this point.

Once you have your bounce method working, add several more obstacles and another jouster. Create two lists to contain the obstacles and the jousters respectively. You should then be able to create a method that uses a nested loop to iterate through every possible match-up of jouster with obstacle, and calls the bounce method for each pair. The idea here is that the call to the bounce method should only appear once in your code.

Test this new method by adding events that allow both jousters to be moved. Once you have everything working, be sure to show the instructor.

Lab 3: Loops and Lists

Introduction

Exercises

Joust Warm-Up: Bouncing Jousters