CSci 1301: Lab 4

Due: Friday, October 19th at 11:59pm

About this lab

Work in groups of 2 or 3.

The lab asks you to build upon examples of Racket "worlds". Racket "worlds" allow you to create programs similar to animations, but worlds are interactive, i.e. they can react to mouse movements, pressed keys, and the like. Functions for worlds are given in the universe.rkt teachpack.

Examples we have considered in class: moving dot (with the changes that we made in class), and recording positions of clicks.

Task 1 (3 points): Changing the clicks example

Study the example of showing the position of clicks: recording positions of clicks. Change it so that it shows empty canvas before the first click (hint: what is the world state before the first click? Add a special case to show for it that just shows a blank scene).

Task 1 (22 points): Improving the moving dot example

Start from the moving dot example that we did in class. Your tasks are as follows:

• Finish changing the example so that the dot never moves off the screen. We have implemented it for the "up" arrow: if the dot is touching the upper border and I press the "up" arrow, it stays in the same position. Implement this functionality for all four sides. Make sure that your code works correctly if the width and height are changed (not necessarily to the same number).
  Use helper functions to move long computations out of the top-level functions.
  Make sure to add check-expects for the new functionality.
• Add handling for the key "c" so that when it's pressed, the dot moves to the center of the canvas.
• Add handling a key "r" (for "random"): when it is pressed, the dot jumps to a random position within the canvas. Here is the description of the function random. Try changing the width and height to see if it's always on the screen.
• Implement handling clicks ("button-up" mouse event) so that a click on the canvas moves the dot to the position that was clicked. Don't forget to include the 'else' part of the condition to leave the dot position unchanged fro any other mouse event.

Extra credit, 10 points: add key handling to change the color of the dot

Copy your current moving dot solution into a separate file: you will be making changes in multiple places.

The only way to keep track of the color of the dot is to incorporate it into the world state. This means expanding the structure that you currently have. You can do it in two different ways: use a nested structure that contains the posn structure and the color, or define your own structure that contains x, y, and a color. Discuss which of these approaches you would like to take and change the world state accordngly. This means changing all the current functions that consume the state (you don't have to copy over all the functionality that you have implemented earlier, just a couple of key events and the mouse event). Use the color part of the structure in show (instead of the current magenta) to display the color.

Test your changes carefully, use a color different from magenta when you provide the initial world state to the big bang.

Pick some letter keys to denote color, for instance "y" for yellow, "g" for green, etc. Make sure they are different from the keys that you use to move the dot. Add these cases to your key event handling functions to change the world state to the color determined by the key. If your show function uses the color in the world state then this should be sufficient to see the color changes. Test your world to see if all events are working as expected.

How to submit

Make sure that your file is named correctly:
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 SmithLeeLab4.rkt If there are others in the class with the same name as yours, you your initial in addition to your last name: MSmithJLeeLab4.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.