;; Width of the final picture
(define WIDTH 512)
;; Height of the final picture
(define HEIGHT 512)
;; Number of grid cells
(define SCALE 64)
;; The width of the grid
(define GWIDTH (/ WIDTH SCALE))
;; The height of the grid
(define GHEIGHT (/ HEIGHT SCALE))

;; Defines a 2D Vector
;; x - The x-value of the vector
;; y - The y-value of the vector
(define-struct vector2d (x y))

; create-gradients: number -> (list of vector)
; Ruft die local Funktion "create" auf
; Bsp: (create-gradients 2) ergibt:
;(list(make-vector2d #i-0.9916790270710302 #i0.5249526803021658)(make-vector2d #i0.5993336254015262 #i0.8165964304676605))
(define (create-gradients n)

  ;create: list number -> (listof vector)
  ;Erzeugt eine Liste, mit der Länge des übergebenen Parameter, von zufälligen Gradienten
  ;Bsp: (create '() 2) ergibt (list (make-vector2d #i0.5557147071202895 #i0.16166538194593366) (make-vector2d #i-0.8928569845064996 #i0.6875843026669924))
  (local
    ((define (create lst n)
     (cond
       [(= n (length lst)) lst]
       [else (create (append lst (cons (make-vector2d (cos(* 2 pi (random))) (sin (* 2 pi (random)))) '()))n)]
       )))
    (create '() n)
    ))


;; fade: number -> number
;; Uses a Sigmoid function to smooth numbers betwenn 0 to 1
;; Example: (fade 1) -> 1
(define (fade t)
  (+ (- (* 6 t t t t t) (* 15 t t t t)) (* 10 t t t))
  )

(check-expect (fade 1) 1)
(check-within (fade 0.5) 0.5 0.001)
(check-within (fade 0.3) 0.16308 0.001)
(check-within (fade 0.8) 0.94208 0.001)

;; Globally store the list of gradients
(define gradients (create-gradients (* (+ 1 GWIDTH) (+ 1 GHEIGHT))))

; linear-interpolation: number number number -> number
; Führt die lineare Interpolation zwischen zwei Werten x,y mit einem Gewicht w durch.
; Bsp: (linear-interpolation 3 4 5) ergibt 8
(define (linear-interpolation x y w)
  (+ (* ( - 1 w) x)(* w y))
)

(check-expect (linear-interpolation 3 4 5) 8)
(check-expect (linear-interpolation 7 8 9) 16)

;dot-grid-gradient: number number number number -> number
;Berechnet das Skalarprodukt von zwei Vektoren
;Bsp: (dot-grid-gradient 5 8 40 50) ergibt 77
(define (dot-grid-gradient ix iy x y)
  (+ (* (- x ix)) (* (- y iy) ))
)


(define (perlin-noise x y)
  1
  )

(define (create-land width height)
  1
  )

;(save-image (color-list->bitmap (create-land WIDTH HEIGHT) WIDTH HEIGHT) "land.png")