    # File lib/compass/sass_extensions/sprites/engines/chunky_png_engine.rb, line 12
            def construct_sprite
              @canvas = ChunkyPNG::Image.new(width, height, ChunkyPNG::Color::TRANSPARENT)
              images.each do |image|
                input_png  = ChunkyPNG::Image.from_file(image.file)
                canvas.replace! input_png, image.left, image.top
              end
            end