CS111 PreLab 4

This prelab introduces you to programming in PictureWorld. You will be writing expressions to produce specific Pictures, and you will also be evaluating expressions to predict the resulting Picture.

Task 1

Task 2

Suppose you are given the following black box method:

public Picture triangle (Color c)
Returns a Picture of a triangle of the specified Color whose vertices are at (0,0), (1,0), and (0,1).

For example,

triangle(Color.green);

Using only the methods in the PictureWorld contract, write (on paper) the expressions which will return the following Pictures:

picture 1

picture 2

picture 3

Task 3

Evaluate the following expressions. Draw (on paper) the Picture that each represents. Indicate the colors in whatever way is convenient (colored pencils, markers,etc.). Do not write a program to run on the computer to show you the pictures; do it by hand! You will be required to do problems like this on the exam, so take this opportunity to practice.

picture 4

overlay(clockwise90(triangle(Color.blue)),triangle(Color.blue));

picture 5

above(fourSame(flipDiagonally(triangle(Color.yellow))),
      beside(triangle(Color.green),
             above(empty(), flipVertically(triangle(Color.green)))));

Time estimates: Do not spend more than 10 minutes on Task 1, 30 minutes on Task 2, and 20 minutes on Task 3. Be sure to try every problem!