line.coffee

class Line

  constructor: (one, two) ->
    @one = one
    @two = two

  m: ->
    (@two.y - @one.y) / (@two.x - @one.x)

  b: ->
    @one.y - (@m() * @one.x)

  y: (x) ->
    (@m() * x) + @b()

  x: (y) ->
    (y - @b()) / @m()

  points: (callback) ->
    points = []
    callback = ((v) -> v) unless callback
    if Math.abs(@one.x - @two.x) > Math.abs(@one.y - @two.y)
      for x in [@one.x..@two.x]
        points.push callback([x, @y(x)])
    else
      for y in [@one.y..@two.y]
        points.push callback([@x(y), y])
    points

world.coffee

line = new Line({x: 3, y: 2}, {x: 7, y: 4})
line.y(3) # 2
line.y(7) # 4
line.x(2) # 3
line.x(4) # 7

line.points() # [[3,2], [4,2.5], [5,3], [6,3.5], [7,4]]