They’re not actually square, though. They’re (on almost any display technology) a mosaic of red green and blue patches arranged inside a square. On a ‘retina’

They’re not actually square, though. They’re (on almost any display technology) a mosaic of red green and blue patches arranged inside a square. On a ‘retina’ class display these square areas are explicitly smaller than the resolution distinguishable by your eyes. Any sharp edges or corners you think you can discern are your mind reconstructing an edge from a series of neural samples on your retina that are the sum of the output of various sub pixel blobs of red green and blue light that focus on that particular cluster of cone cells.