;; title:   Starfield
;; author:  congusbongus, emma bukaceck and phil hagelberg
;; desc:    Draw a starfield with parallax stars
;; license: GPL3+
;; script:  fennel
;; strict:  true
;; tags:    draw parallax effect

;; Adapted from this is my mech by emma bukaceck and phil hagelberg
;; https://tic80.com/play?cart=817

(var t 0)
(var x 96)
(var y 24)
(var STARNEAR 13)
(var STARFAR 14)
(var WIDTH 240)
(var HEIGHT 136)

(local stars [])
(for [i 1 32] (table.insert stars [(math.random 480) (math.random 272)]))

(fn draw-stars [scroll-x scroll-y]
  (each [_ s (ipairs stars)]
    (let [[sx sy] s]
      (pix (% (* (- sx scroll-x) 0.5) WIDTH)
           (% (* (- sy scroll-y) 0.5) HEIGHT) STARFAR)
      (pix (% (- sx scroll-x) WIDTH)
           (% (- sy scroll-y) HEIGHT) STARNEAR))))

(fn _G.TIC []
  (when (btn 0) (set y (- y 1)))
  (when (btn 1) (set y (+ y 1)))
  (when (btn 2) (set x (- x 1)))
  (when (btn 3) (set x (+ x 1)))
  (cls 0)
  (draw-stars x y)
  (spr (+ 1 (* (// (% t 60) 30) 2))
       x y 0 3 0 0 2 2)
  (set t (+ t 1)))

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