Nginx locations for rewrite ordinary images to retina verstion with falback to ordinary if retina version is not present

nginx-retina-rewrite

        ###
        # Retina images handler
        ###
        if ($http_cookie ~* "isRetina=1" ) {
                set $isRetina "retina";
        }

        location ~ ^/bundles/(.*)-retina\.png {
                try_files /bundles/$1-retina.png @retinaFallback;
        }

        location ~ ^/bundles/(.*)\.png$ {
                if ($isRetina = "retina") {
                        rewrite ^/bundles/(.*).png$ /bundles/$1-retina.png last;
                }
        }

        location @retinaFallback {
                rewrite ^/bundles/(.*)-retina.png$ /bundles/$1.png break;
        }
        ##
        # End retina handler
        ##