Using the grid convenience method in JRubyArt (propane)

# A nice method to run a given block for a grid.
# Lifted from action_coding/Nodebox.
def grid(cols, rows, col_size = 1, row_size = 1)
  (0...cols * rows).map do |i|
    x = col_size * (i % cols)
    y = row_size * i.div(cols)
    yield x, y
  end
end

# Creative Coding
# # # # #
# Vera Molnar – 25 Squares
# # # # #
# Interpretation by Martin Vögeli
# Converted to propane Martin Prout
# # # # #
# Based on code by Indae Hwang and Jon McCormack
def settings
  size(600, 600)
end

def setup
  sketch_title '25 Squares'
  rect_mode(CORNER)
  no_stroke
  frame_rate(1) # set the frame rate to 1 draw call per second
end

def draw
  background(180) # clear the screen to grey
  grid_size = 5 # rand(3..12)   # select a rand number of squares each frame
  gap = 5 # rand(5..50) # select a rand gap between each square
  # calculate the size of each square for the given number of squares and gap between them
  cellsize = (width - (grid_size + 1) * gap) / grid_size
  position = -> (count) { gap * (count + 1) + cellsize * count + rand(-5..5) }
  grid(grid_size, grid_size) do |x, y|
    rand(0..5) > 4 ? fill(color('#a11220'), 180.0) : fill(color('#884444'), 180.0)
    rect(position.call(x), position.call(y), cellsize, cellsize)
  end
  # save your drawings when you press keyboard 's' continually
  save_frame('######.jpg') if key_pressed? && key == 's'
end # end of draw