When copying a picture in Jython/Python, how to copy X pixels less with every row

Question

I'm writing a code in Jython, that will copy part of one picture into an empty picture, but I want it to copy (let's say) 10 pixels less with each next row. I don't think I make sense, let me explain with an example. A picture 100 pixels by 100 pixels, the program will copy the first row (100pixels) of pixels into the new picture, but for second row of pixels I want it to copy only 90 pixels, then for the third row 80 pixels, and so on.

Here I have a code that will copy part of a picture, but it copies a square. So what should I add to make it do what I want. I'm guessing I'm supposed to do something with the for x in range but I don't know what.

def copyPic():
  file=pickAFile()
  oldPic=makePicture(file)
  newPic=makeEmptyPicture(getWidth(oldPic),getHeight(oldPic))
  xstart=getWidth(oldPic)/2
  ystart=getHeight(oldPic)/2
    for y in range(ystart,getHeight(oldPic)):
       for x in range(xstart, (getWidth(oldPic))):
         oldPixel=getPixel(oldPic,x,y)
         colour=getColor(oldPixel)
         newPixel=getPixel(newPic,x,y)
         setColor(newPixel,colour)
  explore(newPic)

Answer 1

Your code definitely looks like it will copy the bottom right 1/4 of the image... to make a triangle-shaped piece (or just a piece that has an angle if I understand your question properly) of that section you need to reduce the X maximum value each time through... something like:

def copyPic():
  file=pickAFile()
  oldPic=makePicture(file)
  newPic=makeEmptyPicture(getWidth(oldPic),getHeight(oldPic))
  xstart=getWidth(oldPic)/2
  ystart=getHeight(oldPic)/2

  # The next line gets the max value x can be (width of pic)
  xmax = getWidth(oldPic)

    for y in range(ystart,getHeight(oldPic)):

       # Now loop from the middle (xstart) to the end (xmax)
       for x in range(xstart, xmax):

         oldPixel=getPixel(oldPic,x,y)
         colour=getColor(oldPixel)
         newPixel=getPixel(newPic,x,y)
         setColor(newPixel,colour)

       # Now the x-loop has finished for this line (this value of y)
       # so reduce xmax by 10 (or whatever value) ready for the next line
       xmax = xmax - 10

       # Then you should do some checking in your code to ensure
       # xmax is not < xstart... here is something crude that should work
       if xmax < xstart:
           xmax = xstart

  explore(newPic)

Your code I think will take an image like this:

+------------+
|   1     2  |
|            |
|   3     4  |
|            |
+------------+

and give this:

+-----+
|  4  |
|     |
+-----+

because your X loop is always the same length

By reducing x each time as shown, you should get something like this:

+-----+
|  4 /
|  /
+-

This is not very well coded, and I could rewrite the whole thing... but if you are just learning python then at least the modifications I made to your code should work well with what you already have, and should be easy to follow. I hope that it helps, and feel free to ask for clarification if you need it.

Cheers

PS: I see you asked this twice - you shouldn't ask the same question twice since it splits the answers, and makes it harder for people trying to find answers like this later on...