Css sprite generation

#!/usr/bin/python

import os
import os.path as p
import Image


css_inline_item_template = '''
%(selector)s {
    background: url(%(url)s) no-repeat -%(xpos)spx -%(ypos)spx;
    width: %(width)spx;
    height: %(height)spx;
}
'''

css_base_template = '''
%(base_selector)s {
    background-image: url(%(url)s);
    background-repeat: no-repeat;
}
'''

css_base_item_template = '''
%(selector)s {
    background-position: -%(xpos)spx -%(ypos)spx;
    width: %(width)spx;
    height: %(height)spx;
}
'''


def generate_sprite(images, margin=10):
    def _basename(path):
        return p.splitext(p.basename(path))[0]

    data = []

    master_height = max(*[i.size[1] for i in images])
    master_width = sum([i.size[0] for i in images]) + margin * (len(images) - 1)

    sprite = Image.new(
        mode='RGBA',
        size=(master_width, master_height),
        color=(0,0,0,0))  # fully transparent

    location = 0
    for image in images:
        if 'transparency' in image.info:
            raise Exception('Incorrect transparency mode: ' + image.filename)

        sprite.paste(image,(location, 0))
        data.append({
            'xpos': location,
            'ypos': 0,
            'dir': _basename(p.dirname(image.filename)),
            'file': _basename(image.filename),
            'width': image.size[0],
            'height': image.size[1],
        })
        location += image.size[0] + margin

    return sprite, data

def render_css(base_template, item_template, css_data, sprite_url, base_selector, selector):
    base_info = {
        'base_selector': base_selector,
        'url': sprite_url,
    }
    base_css = base_template % base_info

    items_css = '\n'.join([
        item_template % dict([('selector', selector % image_data)]
            + image_data.items()
            + base_info.items())
        for image_data in css_data])

    return base_css + items_css

def create_sprite_and_css(images_dir, css_output, sprite_output,
        selector='.%(file)s', base_selector='.sprite', url=None, inline=False):
    images = [Image.open(p.join(images_dir, filename))
                for filename in os.listdir(images_dir)
                if not filename.startswith('.')]

    sprite, css_data = generate_sprite(images)
    sprite.save(sprite_output)

    sprite_url = url or p.basename(sprite_output)
    if inline:
        css = render_css('', css_inline_item_template, css_data, sprite_url, base_selector, selector)
    else:
        css = render_css(css_base_template, css_base_item_template, css_data, sprite_url, base_selector, selector)

    css_file = open(css_output, 'w')
    css_file.write(css)
    css_file.close()


if __name__ == '__main__':
    from optparse import OptionParser

    usage = "usage: %prog [options] images_dir css_output sprite_output"
    parser = OptionParser(usage=usage)
    parser.add_option("-i", "--inline", action="store_true", dest="inline", default=False,
                      help="When set, image url will be put in css rule for every item.")
    parser.add_option("-s", "--selector", dest="selector", default='.%(file)s',
                      help="Selector template. You can use dir, file, width, height here.")
    parser.add_option("-S", "--base-selector", dest="base_selector", default='.sprite',
                      help="Base selector template for base css rule (when -i is not set).")
    parser.add_option("-u", "--url", dest="url", default='',
                      help="Css rule Image url template.")

    (options, args) = parser.parse_args()

    if len(args) < 3:
        print 'You must provide all 3 arguments.'
    else:
        images_dir, css_output, sprite_output = [p.realpath(arg) for arg in args]
        create_sprite_and_css(images_dir, css_output, sprite_output,
                selector=options.selector,
                base_selector=options.base_selector,
                inline=options.inline,
                url=options.url)