var shader = (function(){
  var fn_str, fn, lex
  var exports = {}
  var animating = false
  
  exports.init = function(){
    lex = new Lex (0, 0)
    exports.build(demo_shader.innerHTML)
  }
  exports.build = function (fn_str){
    try {
      new_fn = new Function('lex', 'x', 'y', 'w', 'h', 't', fn_str)
      new_fn(lex, 0, 0, 1, 1, 0)
    }
    catch (e) {
      throw 'Shader execution error'
    }
    exports.fn = fn = new_fn
    return fn
  }
  exports.run = function(canvas){
    var t = +new Date
    var shader_canvas = selection.hidden ? canvas : selection.canvas;
    var w = shader_canvas.w, h = shader_canvas.h
    shader_canvas.forEach(function(lex, x, y){
      fn(lex, x, y, w, h, t)
      lex.build()
    })
  }
  exports.toggle = function(state){
    animating = typeof state == "boolean" ? state : ! animating
    return animating
  }
  exports.pause = function(){
    animating = false
  }
  exports.play = function(){
    animating = true
  }
  exports.animate = function (t){
    requestAnimationFrame(exports.animate)
    if (! animating) { return }
    exports.run(canvas)
  }
  
  return exports

})()