Using a cond in a let form makes me feel a little greasy

texture-generators.lisp

(defvar *grass-base-color* (list 64 137 44))
(defvar *grass-medium-color* (mapcar (lambda (x) (round (* x 0.9))) *grass-base-color*))
(defvar *grass-dark-color* (mapcar (lambda (x) (round (* x 0.8))) *grass-base-color*))

(defun generate-grass-texture2 (file width height)
  (let* ((png (make-instance 'zpng:png
                             :color-type :truecolor-alpha
                             :width width
                             :height height))
         (image (zpng:data-array png)))
    (loop for x from 0 below width do
         (loop for y from 0 below height do
              (let* ((chance (random 4))
                     ; 25% chance for the dark color, 50% for medium, 25% for bright
                     (color (cond ((= 0 chance)
                                   *grass-dark-color*)
                                  ((or (= 1 chance)
                                       (= 2 chance))
                                   *grass-medium-color*)
                                  (t *grass-base-color*))))
                (setf (aref image y x 0) (elt color 2))
                (setf (aref image y x 1) (elt color 1))
                (setf (aref image y x 2) (elt color 0))
                (setf (aref image y x 3) 255))))
    (zpng:write-png png file)))