Squares rotating in Elm (old-style w/ Signal)

rotating.gif

Squares.elm

-- http://ec2-52-202-34-228.compute-1.amazonaws.com:8000/examples/shapes

import Color exposing (..)
import Graphics.Collage exposing (..)
import Graphics.Element exposing (..)
import Time exposing (..)

radius    = 150
clearGrey = rgba 111 111 111 0.6
blueish   = hsl (degrees (180+35)) 0.5 0.4
greenish  = hsl (degrees (180-35)) 0.5 0.4

main =
  Signal.map squares (every millisecond)

squares t =
  let
    style color =
      traced
        { width      = 20
        , color      = color
        , cap        = Round
        , join       = Smooth
        , dashing    = []
        , dashOffset = 0
        }
    outerSquares = 
      List.map outerSquare (cornersFor radius)
    outerSquare center =
      square (radius-40) center
      |> style blueish
      |> rotate (degrees -t/10)
    innerSquare =
      square radius (0, 0)
      |> (style greenish)
      |> rotate (pi/4)
      |> rotate (degrees t/10)
  in
    collage 700 700 ([innerSquare] ++ outerSquares)

square radius center =
  let
    corners = cornersFor radius
    addVec (x1, y1) (x2, y2) = (x1+x2, y1+y2)
    squarePoints =
      case List.head corners of
        Just first -> corners ++ [first]
        Nothing    -> corners
    squarePath =
      List.map (addVec center) squarePoints
  in
    path squarePath

cornersFor r =
  [ ( r,  0)
  , ( 0,  r)
  , (-r,  0)
  , ( 0, -r)
  ]