Week 2

1
Week 2
2
Homework

• Are you collaborating effectively?
• Are you starting early?
• Are you running your homework code to see if it
  works?
• Homework 2 is now posted.
• Due this coming Friday night at midnite!

3
Prequiz

• Are you collaborating effectively?

4
What have we learned so far?

• Basics of writing a computer program in Jython
  using JES
• Names
• Quantities (Numbers)
• Things (Pictures, strings)
• Functions
• Files

5
Have you actually written a computer program?

• Yes?/No?
• Why doesn't it look like a computer program?

6
JES commands

• def
• pickAFile()
• picture makePicture(filename)
• thePixels getPixels(picture)
• getRed(pixel), getGreen(pixel), getBlue(pixel)
• setRed(pix, col), setGreen..., setBlue...
• color makeColor(r, g, b)
• setColor(pixel, color)
• show(picture)
• showVars()

7
Can a function call a function?
8
Can a function that you write call a function
that you write?
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Example

• def grayScale(picture)
• for px in getPixels(picture)
• r getRed(px) 0.299
• g getGreen(px) 0.587
• b getBlue(px) 0.114
• lum r g b
• setColor(px, makeColor(lum, lum, lum)
  
• def grayPicker()
• pic makePicture(pickAFile())
• grayScale(pic)
• show(pic)
• Should this function return something?

10
New Material
11
MediaPath

• As a convenience, Jython contains a name called
  MediaPath. You don't use this name directly.
  Instead you use two functions
• setMediaPath()
• Opens a file chooser window
• Allows you to choose a directory!
• Sets MediaPath to the value of that directory
  path which is a string
• getMediaPath("filename")
• returns the value of MediaPath concatenated with
  the "filename"

12
range()

• The "for loop" in JES allows you to create a loop
  structure and have a "loop variable" take on all
  of the different value in a collection
• for px in getPixels(picture)
• You can even make up a collection
• for loopvar in 1, 3, "apple", 7000
• But sometimes you just want to have a loop run
  with the loop variable having an increasing (or
  decreasing) sequence of integers
• Enter the range function!

13
Individual Pixel Manipulation

• So far we have seen operations on a whole
  collection of pixels ( i.e. getPixels(picture) )
• But sometimes we would like to be able to be more
  selective in out manipulation of pixels
• pixel getPixel(picture, x, y)

14
Picture Size

• With getPixels we basically had a collection of
  pixels we could go through one at a time
• With getPixel things get a little more complex.
  Now we have to specifiy the x and y of the pixel.
• How do we even know the size of a picture?
• width getWidth(picture)
• height getHeight(picture)

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Nested for Loops
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Selective Manipulation
(x1,y1)
(x2,y2)
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Nested for Loops

• def nested(pict)
• for x in range(1, getWidth(pict)1)
• for y in range(1, getHeight(pict)1)
• pix getPixel(pict, x, y)
• Do whatever processing you want
• to the pixel here!

18
Homework 2 Template

• def hw2()
• mypic
• makePicture(getMediaPath('myPicFile.jpg'
  ))
• Call your function that will modify the pic
• Just as an example
• nested(mypic)
• show(mypic)

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Homework 2 Checklist

• Write a function (or functions) that will
  manipulate a picture.
• Make sure that your program uses getMediaPath
• Put the program and file in the same folder
• Using WebWork turn BOTH files in as hw2
• Make sure to retrieve the submission and run it
  just like the grader will run it!!!

20
Translating

• Can we put a picture wherever we want it?

21
Another Useful Tool

• makeEmptyPicture(width, height)
• Can you guess what it does?
• Can you guess what it returns?

22
Idea

• Let's make up our own "picture" from scratch!

23
Where?
(xpos, ypos)
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Scaling

• Can we make pictures bigger or smaller?
• Can we stretch them?