This patterned poem is by the Danish poet lacobus Nicholae de Dacia, otherwise Jakob
Nielsen, who wrote around 1363 to 1379. It is from his Liber de distinccione metrorum, which was later bound into a big manuscript in the British Library called Cotton Claudius A. (X iv, folio 25 E, to be precise), which does not seem to have been scanned and put online yet. It made its way onto the web when it appeared on the cover of a periodical called Visible Language.