CMSC 10500, Fall 2012. Lab 2 -- Have an Okay Day!

A. Preliminaries

1. Style

function-name : first-input-type second-input-type ... -> output-type

rectangle-area : num num -> num

since it takes two numbers (the width and height) as input, and returns a number corresponding to the area.

A quick note about coding style: Indentation and line-breaks make your code easy to read and are good programming practices, so please pay attention to them. For example, here's a definition for the area of a trapezoid:

;; trapezoid-area : num num num -> num
;; computes the area of a trapezoid using the standard formula
(define (trapezoid-area base top height) (* height (/ (+ base top) 2)))

;; trapezoid-area : num num num -> num
;; computes the area of a trapezoid using the standard formula
(define (trapezoid-area base top height)
   (* height
      (/ (+ base top)
         2)))

2. Setup

• Updating your repository
  • If you are working on your laptop and have already checked out the repository, you will not need to check it out again -- just navigate to the yourusername-cs105-aut-12 directory that you've checked out, and type svn update.

  • If you are on the MacLab computers, open up the Terminal from the Dock. You will have to check out your SVN repository again, since the MacLab computers erase old files.

    Type svn co https://phoenixforge.cs.uchicago.edu/svn/yourusername-cs105-aut-12 into the Terminal, replace yoursername with your CNet username. If you get a prompt asking you if you would like to accept the certificate, press p (meaning to accept permanently). Enter your CNet password when prompted for it.

• Look into the contents of the directory after checking it out. You will see the directory for lab1 containing your previous work and your grade, as well as any other work you have committed for hw1.
  Now in the Terminal window, create your lab2 directory.

  mkdir lab2

  Now click on this lab2.rkt link to download the lab2.rkt file and save it in your yourusername-cs105-aut-12/lab2 directory you just created. Now remember we only made local copies of your lab2 directory and lab2.rkt so you need to svn add these files to your repository. Type in the following commands:

  svn add lab2
  cd lab2
  svn add lab2.rkt

  Next, you will commit the lab2 directory to the repository. Remember we only told svn that on the next commit it should add the lab2 directory. Type in the following commands

  cd ..
  svn commit -m "Commiting the lab2 directory"

  Note: cd .. takes you up one level in your directory structure (i.e. yourusername-cs105-aut-12/lab2 )
• Click the DrRacket icon on the dock, which should launch the DrRacket program. Click on File->Open. Select your home directory on the left panel (the icon of a home with your username next to it), and then navigate to yourusername-cs105-aut-12/lab2. Click on lab2.rkt to open it.

You may use any DrRacket operator for this lab except the scale function.

B. Simple Definitions

• Define a variable named baseface that draws an yellow circle of radius 75.

  

• What if the user wanted to specify the radius of the circle, rather than having it hard-coded in the program? In that case, we would like to define a function that takes that radius as a parameter instead.

  Define a function with the contract

  blankface: num -> image

  that draws a circle with the specified radius, of the color yellow if the radius is at least 75, and orange if the radius is less than 75. For example, (blankface 50) should draw an orange circle of radius 50, and (blankface 150) a yellow circle of radius 150. Use the cond statement you learned about in class.

C. Generating Parts of a Face

• Define a function

  eye : num -> image

  which draws a cartoon-like eye of width = the input number, and height = twice the input number. For example, (eye 10) should produce something like

  

  Use the ellipse function.

• Write the function

  mouth : num -> image

  which draws a grim mouth of width = the input number. Use the rectangle function. For example, (mouth 100) should produce something like

  

  and (mouth 50) something like

  

  (Notice how the height of the mouth is proportional to the width.)

D. Generating a Face

• Use the overlay, overlay/xy, and/or underlay/xy operators in conjuction with the functions you just wrote above to write the function

  face : num -> image

  which generates a face. (face 50) should look approximately like this:

  

  and (face 120) like this:

  

  Don't sweat the small details of eye and mouth placement -- just make sure it looks more or less like a face. Make sure the entire face scales with the radius -- that is the sizes and positions of the eyes and mouth should be appropriate for the given radius. To test that it scales, uncomment the last expression before Part E in lab2.rkt (starting with beside), giving an output like this:

  

  You are encouraged to write more auxiliary functions if it will make your task easier. The face function will be reasonably complex, so make sure you are indenting correctly.

E. Happy and Sick Faces

• Write a function

  smiley-face : num -> image

  that produces a face of the given radius with a smile. The color should be orange or yellow depending on the radius just as before. If you uncomment the second-last expression in lab2.rkt, you should get something like this:

  

  Hint: write a separate auxiliary function to create a smile. One way of getting the smile is to overlay two circles of the appropriate colors, and then crop the result midway. Use the crop function.

• Write a function

  sick-face : num -> image

  that produces a face of the given radius with a frown and Xs as eyes. The color should be orange or yellow depending on the radius just as before. If you uncomment the last expression in lab2.rkt, you should get something like:

  

  Writing a function to produce a frown should involve a minor adaptation of the smile function.

  Hint: To get the Xs write an additional function that uses the rectangles, rotate,and overlay functions.

svn commit -m "BLAH"