Pretty much all of them work in 2x2 quads. DyDx is calculated within a quad. But, not across them. This is an imperfect approximation to the derivative that ne

Pretty much all of them work in 2x2 quads. DyDx is calculated within a quad. But, not across them. This is an imperfect approximation to the derivative that needs to be accounted for. But, it’s useful and very cheap and trivially easy.