pixen_to_gameQuery.rb

module PixenToGameQuery
  require 'RMagick'
  include Magick

  FPR = 12      # Frames per row in a sprite sheet generated by Pixen
  COLPAD = 2    # Pix between each column of images on the sprite sheet
  ROWPAD = 2    # Pix between each row of images on the sprite sheet
  LEFTPAD = 4   # Extra pix on left of sprite sheet
  RIGHTPAD = 20 # Extra pix on right of sprite sheet
  BOTTOMPAD = 2 # Extra pix on bottom of sprite sheet

  def PixenToGameQuery.convert_sprite(image_path, width, height, frames, new_image_path)
  
    original = ImageList.new(image_path)
    img = Image.new((width + COLPAD) * frames, height)
    sprite_rows = (frames.to_f / FPR).ceil
  
    0.upto(sprite_rows - 1) do |rownum|
      rowframes = (rownum == sprite_rows - 1) ? frames % FPR : FPR
      row_width = rowframes * (width + COLPAD)
      pix = original.get_pixels(LEFTPAD,
                                ROWPAD + (height + ROWPAD) * rownum,
                                row_width,
                                height)
      img.store_pixels(rownum * FPR * (width + COLPAD),
                       0,
                       row_width,
                       height,
                       pix)
    end
  
    img.write(new_image_path)
  end
end

This is a simple script that uses RMagick to convert a sprite sheet created by Pixen and convert it to a single-row sprite suitable for use with the gameQuery library. Pixen automatically creates rows of 12 frames each and puts some extra padding in. This script accounts for that and trims the image down and puts all the frames in a single row.

image_path: path to the file generated by Pixen
width: the width of a single frame
height: the height of a single frame
frames: the total number of frames in the animation
new_image_path: the path to write the new file to

Minor changes to encapsulate the code in a Module and change filename to match module name.