CS 101 - Introduction to Computing, Spring 2007

Lab 9

This lab assignment will have you write at least two functions in jython that will create a new image that will be a 90 degree rotation in the clockwise direction of another image. This lab is to focus on the use of the return statement in JES and having a function do one and only one thing.

Reminder

In the ACCC Labs that have JES, it can be found by:

1. Clicking on Start
2. Then click on All Programs
3. Then click on Class Applications
4. Then click on Engineering
5. Finally click on Jython Environment for Students

Rotating an image

def rotate90counterclockwise(): # Set up the source and target pictures file = pickAFile() pict = makePicture(file) wid = getWidth (pict) hgt = getHeight (pict) canvas = makeEmptyPicture(hgt, wid) # Now, do the actual copying--swap X & Y (correctly)! targetX = 1 for sourceX in range(1,getWidth(pict)): targetY = 1 for sourceY in range(1,getHeight(pict)): color = getColor(getPixel(pict,sourceX,sourceY)) setColor(getPixel(canvas, targetY, wid - targetX), color) targetY = targetY + 1 targetX = targetX + 1 show(pict) show(canvas) return canvas

To do the rotation we need to figure out the corresponding positions of the pixels in the original image and the rotated image. During lecture for the counter-clockwise rotation, we determined that:

• rotated X = original Y
• rotated Y = original Width - original X

Lab Assignment 9

Create a file using JES that will:

1. Contain a comment indicating
   • your Name,
   • Net-ID,
   • Course Name,
   • Assignment Name and
   • a short description of the assignment

2. Contain a JES function that will
   • allow the user to pick an image using pickAFile().
   • create the JES image
   • call the function rotate90 () and save the image this function returns.
   • display the new rotated image
   • allow the user to save the new rotated image where the name of the file is determined by using pickAFile().

3. Contain a JES function called rotate90 () that will:
   • take 1 parameter: the image to be rotated.
   • create a new empty image just large enough to hold the rotated image. You are expected to use makeEmptyPicture () for this.
   • copy the pixels from the original image passed in as the parameter to the new image
   • return the rotated image using the return statement.
   This function may call other functions that are built-in to JES or that you have written. Note that the code give above is close to what is needed here but it is not exact. Other than rotating in the wrong direction, the above function does more that just one thing.

Submittal of the Lab Assignment

• You are submit your program electronically by placing it in the digital drop box in blackboard.
• You are also required to submit the image that you selected the x-start, y-start, x-end and y-end values.
• Programs that are correct and submitted by noon on the Wednesday the lab assignment is discussed will receive an extra 10% on the score of the lab.
• When saving your program, use a meaningful name like lab9.py.
• When submitting your lab assignment, place all of the needed files it in a zippped folder (even if you are only submitting one file) with the name of yournetid_labNum and submit that zipped folder to the digital drop box. For instance, if your net id is abc32 then the folder name should be abc32_lab9.

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