diamonds.elm

import Text exposing (..)
import Color exposing (..)
import Graphics.Element exposing (..)
import Graphics.Collage exposing (..)
import List
import Time exposing (Time, fps, timestamp)
import Signal exposing ((<~))

main =
  let
    delta = fps 60
    sizes' = sizes (List.length colors) 100
    angles = (\(t, _) -> angle t) <~ timestamp delta
    anglesSignal = Signal.sampleOn delta angles
  in
    (\a -> collage 200 200 (diamonds sizes' a)) <~ anglesSignal

diamonds : List Float -> Float -> List Form
diamonds sizes angle =
  List.map2 (,) colors sizes
  |> List.map (\(color, size) -> diamond color size angle)

angle timestamp =
  toFloat ((round (timestamp / 10)) % 360)

sizes : Int -> Int -> List Float
sizes n max =
  let
    step = 20
    start = max // step
    stop = (max - n*step) // step
  in
    downTo start stop
    |> List.map (\n -> n * step)
    |> List.map toFloat

downTo : Int -> Int -> List Int
downTo start stop =
  let n = (start - stop) + 1
  in
    List.reverse [1..n]

colors : List Color 
colors =
  [red, orange, yellow, green, blue, purple]

diamond : Color -> Float -> Float -> Form
diamond color size angle =
  square size
    |> filled color
    |> rotate (degrees angle)