CoffeeScript version of simplex noise and a simple RNG useful for seeding.

noise.js.coffee

# Ported from Stefan Gustavson's java implementation
# http://staffwww.itn.liu.se/~stegu/simplexnoise/simplexnoise.pdf
# Read Stefan's excellent paper for details on how this code works.
#
# Sean McCullough banksean@gmail.com

{floor, sqrt} = Math

class @Noise
  grad3: [
    [1,1, 0], [-1,1, 0], [1,-1,0], [-1,-1,0], [1,0, 1], [-1, 0, 1]
    [1,0,-1], [-1,0,-1], [0, 1,1], [ 0,-1,1], [0,1,-1], [ 0,-1,-1]
  ]

  # A lookup table to traverse the simplex around a given point in 4D.
  # Details can be found where this table is used, in the 4D noise method.
  simplex: [
    [0,1,2,3], [0,1,3,2], [0,0,0,0], [0,2,3,1], [0,0,0,0], [0,0,0,0]
    [0,0,0,0], [1,2,3,0], [0,2,1,3], [0,0,0,0], [0,3,1,2], [0,3,2,1]
    [0,0,0,0], [0,0,0,0], [0,0,0,0], [1,3,2,0], [0,0,0,0], [0,0,0,0]
    [0,0,0,0], [0,0,0,0], [0,0,0,0], [0,0,0,0], [0,0,0,0], [0,0,0,0]
    [1,2,0,3], [0,0,0,0], [1,3,0,2], [0,0,0,0], [0,0,0,0], [0,0,0,0]
    [2,3,0,1], [2,3,1,0], [1,0,2,3], [1,0,3,2], [0,0,0,0], [0,0,0,0]
    [0,0,0,0], [2,0,3,1], [0,0,0,0], [2,1,3,0], [0,0,0,0], [0,0,0,0]
    [0,0,0,0], [0,0,0,0], [0,0,0,0], [0,0,0,0], [0,0,0,0], [0,0,0,0]
    [2,0,1,3], [0,0,0,0], [0,0,0,0], [0,0,0,0], [3,0,1,2], [3,0,2,1]
    [0,0,0,0], [3,1,2,0], [2,1,0,3], [0,0,0,0], [0,0,0,0], [0,0,0,0]
    [3,1,0,2], [0,0,0,0], [3,2,0,1], [3,2,1,0]
  ]

  constructor: (random=Math.random) ->
    @p = (floor(random() * 256) for i in [0...256])
    # To remove the need for index wrapping, double the permutation table length
    @perm = (@p[i & 255] for i in [0...512])

  dot: (g, x, y) ->
    g[0] * x + g[1] * y

  at: (xin, yin) ->
    # Skew the input space to determine which simplex cell we're in
    F2 = 0.5*(sqrt(3.0)-1.0)
    s = (xin+yin)*F2 # Hairy factor for 2D
    i = floor(xin+s)
    j = floor(yin+s)
    G2 = (3.0-sqrt(3.0))/6.0
    t = (i+j)*G2

    # Unskew the cell origin back to (x,y) space
    X0 = i-t
    Y0 = j-t

    # The x,y distances from the cell origin
    x0 = xin-X0
    y0 = yin-Y0

    # For the 2D case, the simplex shape is an equilateral triangle.
    # Determine which simplex we are in.
    # Offsets for second (middle) corner of simplex in (i,j) coords
    if x0 > y0
      # lower triangle, XY order: (0,0)->(1,0)->(1,1)
      i1=1
      j1=0
    else
      # upper triangle, YX order: (0,0)->(0,1)->(1,1)
      i1=0
      j1=1
    # A step of (1,0) in (i,j) means a step of (1-c,-c) in (x,y), and
    # a step of (0,1) in (i,j) means a step of (-c,1-c) in (x,y), where
    # c = (3-sqrt(3))/6
    x1 = x0 - i1 + G2 # Offsets for middle corner in (x,y) unskewed coords
    y1 = y0 - j1 + G2
    x2 = x0 - 1.0 + 2.0 * G2 # Offsets for last corner in (x,y) unskewed coords
    y2 = y0 - 1.0 + 2.0 * G2
    # Work out the hashed gradient indices of the three simplex corners
    ii = i & 255
    jj = j & 255
    gi0 = @perm[ii+@perm[jj]] % 12
    gi1 = @perm[ii+i1+@perm[jj+j1]] % 12
    gi2 = @perm[ii+1+@perm[jj+1]] % 12
    # Calculate the contribution from the three corners
    t0 = 0.5 - x0*x0-y0*y0
    if t0 < 0
      n0 = 0.0
    else
      t0 *= t0
      n0 = t0 * t0 * @dot(@grad3[gi0], x0, y0)  # (x,y) of grad3 used for 2D gradient
    t1 = 0.5 - x1*x1-y1*y1
    if t1 < 0
      n1 = 0.0
    else
      t1 *= t1
      n1 = t1 * t1 * @dot(@grad3[gi1], x1, y1)
    t2 = 0.5 - x2*x2-y2*y2
    if t2 < 0
      n2 = 0.0
    else
      t2 *= t2
      n2 = t2 * t2 * @dot(@grad3[gi2], x2, y2)
    # Add contributions from each corner to get the final noise value.
    # The result is scaled to return values in the interval [-1,1].
    70.0 * (n0 + n1 + n2)

random.js.coffee

{floor, random} = Math

# This is a pretty weak, but fit-for-purpose seedable RNG.
# Credit: http://stackoverflow.com/questions/424292#answer-424445
class @Random
  constructor: (@state) ->
    # LCG using GCC's constants
    @m = 0x80000000 # 2**31
    @a = 1103515245
    @c = 12345

    @state ?= floor(random() * (@m - 1))

  nextInt: ->
    @state = (@a * @state + @c) % @m

  nextFloat: ->
    @nextInt() / (@m - 1)

  nextRange: (start, end) ->
    # returns in range [start, end): including start, excluding end
    # can't modulu nextInt because of weak randomness in lower bits
    rangeSize = end - start
    randomUnder1 = @nextInt() / @m
    start + floor(randomUnder1 * rangeSize)

  choice: (array) ->
    array[@nextRange(0, array.length)]