White gridlines over image using JES (python)

Question

How can I write a program using JES to draw “White” gridlines on an image where the horizontal gridlines are separated by 10 pixels and the vertical gridlines are separated by 20 pixels?

Answer 1

Yes, surprisingly, addLine(picture, startX, startY, endX, endY) can only draw black lines !?

So let's do it by hand. Here is a very basic implementation:

def drawGrid(picture, color):

  w = getWidth(picture)
  h = getHeight(picture)

  printNow(str(w) + " x " + str(h))

  w_offset = 20  # Vertical lines offset
  h_offset = 10  # Horizontal lines offset

  # Starting at 1 to avoid drawing on the border
  for y in range(1, h):     
    for x in range(1, w):
      # Here is the trick: we draw only 
      # every offset (% = modulus operator)
      if (x % w_offset == 0) or (y % h_offset == 0):
        px = getPixel(picture, x, y)
        setColor(px, color)


file = pickAFile()
picture = makePicture(file) 
# Change the color here
color = makeColor(255, 255, 255) # This is white
drawGrid(picture, color)
show(picture)

Note : this could also have been achieved a lot more efficiently using the function drawLine(), from the script given here.

Output:

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