transient crop

gistfile1.txt

(defn crop-old
  [ctx w h]
  (let [data  (.-data (.getImageData ctx 0 0 w h))
        s     (* w h 4)
        [a b] (loop [y 0 px [] py []]
                (if (< y h)
                  (let [[x' y']
                    (loop [x 0 px' px py' py]
                      (if (< x w)
                        (let [a? (> (aget data (+ (* (+ (* y w) x) 4) 3)) 0)]
                          (recur (inc x) (if a? (conj px' x) px') (if a? (conj py' y) py')))
                        [px' py']))]
                  (recur (inc y) x' y'))
                  [px py]))
        px    (sort a)
        py    (sort b)
        n     (- (count px) 1)
        w'    (- (last px) (first px))
        h'    (- (last py) (first py))
        cut   (.getImageData ctx (first px) (first py) w' h')
        c     (create-canvas w' h')
        cx    (.getContext c "2d")]
    (.putImageData cx cut 0 0)
    (.toBuffer c)))

(defn crop
  [ctx w h]
  (let [data  (.-data (.getImageData ctx 0 0 w h))
        s     (* w h 4)
        [a b] (loop [y 0 px (transient []) py (transient [])]
                (if (< y h)
                  (let [[x' y']
                    (loop [x 0 px' px py' py]
                      (if (< x w)
                        (let [a? (> (aget data (+ (* (+ (* y w) x) 4) 3)) 0)]
                          (recur (inc x) (if a? (conj! px' x) px') (if a? (conj! py' y) py')))
                        [px' py']))]
                  (recur (inc y) x' y'))
                  [(persistent! px) (persistent! py)]))
        px    (sort a)
        py    (sort b)
        n     (- (count px) 1)
        w'    (- (last px) (first px))
        h'    (- (last py) (first py))
        cut   (.getImageData ctx (first px) (first py) w' h')
        c     (create-canvas w' h')
        cx    (.getContext c "2d")]
    (.putImageData cx cut 0 0)
    (.toBuffer c)))