triangle index functions

tris.clj

(defn tri-strip
  ([size] (tri-strip 0 size))
  ([start size]
   (->> (range start (+ start size))
        (partition 4 1)
        (map (fn [[a b c d]] [a b c
                              c b d]))
        flatten)))

(defn tri-fan
  ([size] (tri-fan 0 size))
  ([start size]
   (->> (range (inc start) (+ start size))
        (partition 2 1)
        (map #(conj % start))
        flatten)))

(defn tris
  ([size] (tris 0 size))
  ([start size]
   (->> (range start (+ start size))
        (partition 3)
        flatten)))