def task_generate_decktape_slides(unit, source, output):
    """Get the description of the Decktape slides generation task.

    :sig: (kirlent.Unit, Path, Path) -> TaskDesc
    :param unit: Unit to generate the slides for.
    :param source: Source file of the RevealJS slides.
    :param output: Slides file to store the result.
    :return: Task description.
    """
    decktape_args = ['decktape', '-s', '%(size)s', 'file:///%(path)s',
        '%(file)s']
    decktape_cmd = ' '.join(decktape_args) % {'size': '1121x795', 'path':
        source.absolute(), 'file': output}
    return {'basename': 'generate_decktape', 'name': unit.slug, 'actions':
        [decktape_cmd], 'file_dep': [source], 'targets': [output]}
