bezier.coffee

# Pass this function an array of points from http://wtcurve.surge.sh
# and a value between 0 and 1, to get an eased result.
bezierEase = (points, goal)->
  a = 0
  b = 1
  p = null
  attempts = 0
  while attempts++ < 20 # Set a reasonable upper limit on time spent finding the right result
    mid = (a + b)/2
    p = evalCurve points, mid
    if Math.abs(p[0] - goal) < 0.0001 # Tends to finish in around 10 attempts
      return p[1]
    if p[0] < goal then a = mid else b = mid
    null # Null at the end of a loop stops CoffeeScript from creating a "results" array
  return p[1]

evalCurve = (points, t)->
  while points.length > 1
    nextPoints = []
    for a, i in points when i < points.length-1
      b = points[i+1]
      dx = b[0] - a[0]
      dy = b[1] - a[1]
      nx = a[0] + dx * t
      ny = a[1] + dy * t
      nextPoints.push [nx, ny]
      null
    points = nextPoints
    null
  return points[0]