If there’s one constant in fashion, it’s this: Anna Sui knows how to deliver on a high-octane, rocking runway. And she didn’t miss a beat for spring with her spunky Sixties lineup. Actually, make that a Swinging Sixties-meets-19th-century England romp, because Sui also found inspiration in the circus scene of the 1967 film, “Doctor Dolittle.” She played a deft ringmaster — piled-on patchwork, Liberty prints and colors — to dazzling effect. There was the parade of playful print dresses, accented with Peter Pan collars, embroidered trims or adorable abbreviated ties; the cutely corded majorette capelets and vests, and quieter moments as well, amidst all that pretty hustle and bustle. Case in point: the purple cable-knit sweater, with puffy leg-of-mutton sleeves. Also groovy: men’s wear references aplenty in peppy pantsuits and waistcoats. And no tribute to “Doctor Dolittle” would be complete without nods to the beastly bunch, which Sui rendered with charm: intarsia lions and bewitching animal-shaped ballet flats — pure fun.