    # File lib/compass/sass_extensions/sprites/layout_methods.rb, line 121
            def calculate_horizontal_positions
              @images.each_with_index do |image, index|
                image.top = image.position.unit_str == '%' ? (@height - image.height) * (image.position.value / 100.0) : image.position.value
                next if index == 0
                last_image = @images[index-1]
                image.left = last_image.left + last_image.width + [image.spacing, last_image.spacing].max
              end
            end