public function addClass(ResponsiveImageClass $class)
    {
        $this->classes_added = true;
        if (array_key_exists($class->getName(), $this->classes)) {
            throw new \Exception(sprintf('A responsive image class with name "%s" is already registered', $class->getName()));
        }
        if ($this->default_filters instanceof FilterInterface) {
            $class->addFilter($this->default_filters);
        }
        if ($this->default_post_filters instanceof FilterInterface) {
            $class->addPostFilter($this->default_post_filters);
        }
        if ($this->default_scaling_algorithm != '') {
            $class->setScaleAlgorithm($this->default_scaling_algorithm);
        }
        if ($this->default_output_type_map instanceof OutputTypeMap) {
            $class->setOutputTypeMap($this->default_output_type_map);
        }
        $this->classes[$class->getName()] = $class;
    }