var patterns = {}
patterns[2] = [ 0, 2,
                3, 1 ]

patterns[3] = [ 0,  5,  3,
                8,  1,  6,
                4,  7,  2, ]

patterns[4] = [ 0,  8,  2, 10,
                6, 14,  4, 12,
                3, 11,  1,  9,
                5, 13,  7, 15  ]

CanvasQuery.Wrapper.prototype.threshold = function(factor) {
  var bitmap = this.context.getImageData(0, 0, this.canvas.width, this.canvas.height)
  var bitmapData = bitmap.data

  var width = this.canvas.width
  var height = this.canvas.height

  if (factor < 1) factor *= 255

	for (var i = 0; i < height; i++) {
		for (var j = 0; j < width; j++) {
			var a = 4 * (i*width + j)
			var val = (bitmapData[a] + bitmapData[a+1] + bitmapData[a+2]) / 3
      var lum = val > factor ? 255 : 0
			bitmapData[a] = bitmapData[a+1] = bitmapData[a+2] = lum
    }
  }
  this.context.putImageData(bitmap, 0, 0);
  return this;
}

CanvasQuery.Wrapper.prototype.randomDither = function() {
  var bitmap = this.context.getImageData(0, 0, this.canvas.width, this.canvas.height)
  var bitmapData = bitmap.data

  var width = this.canvas.width
  var height = this.canvas.height

	for (var i = 0; i < height; i++) {
		for (var j = 0; j < width; j++) {
			var a = 4 * (i*width + j)
			var val = (bitmapData[a] + bitmapData[a+1] + bitmapData[a+2]) / (3*255)
      var lum = val > Math.random() ? 255 : 0
			bitmapData[a] = bitmapData[a+1] = bitmapData[a+2] = lum
    }
  }
  this.context.putImageData(bitmap, 0, 0);
  return this;
}

CanvasQuery.Wrapper.prototype.pattern2Dither = function() {
  this.patternDither(2)
}
CanvasQuery.Wrapper.prototype.pattern3Dither = function() {
  this.patternDither(3)
}
CanvasQuery.Wrapper.prototype.pattern4Dither = function() {
  this.patternDither(4)
}
CanvasQuery.Wrapper.prototype.patternDither = function(n) {
  var bitmap = this.context.getImageData(0, 0, this.canvas.width, this.canvas.height)
  var bitmapData = bitmap.data

  var width = this.canvas.width
  var height = this.canvas.height

  var pat = patterns[n]
  var len = pat.length - 1

	for (var i = 0; i < height; i++) {
		for (var j = 0; j < width; j++) {
      var p = ((i % n) * n) + (j % n)
			var a = 4 * (i*width + j)
			var val = (bitmapData[a] + bitmapData[a+1] + bitmapData[a+2]) / (3*255)
      var lum = val > pat[p]/len ? 255 : 0
			bitmapData[a] = bitmapData[a+1] = bitmapData[a+2] = lum
    }
  }
  this.context.putImageData(bitmap, 0, 0);
  return this;
}

CanvasQuery.Wrapper.prototype.pattern2LiteDither = function() {
  this.patternLiteDither(2)
}
CanvasQuery.Wrapper.prototype.pattern3LiteDither = function() {
  this.patternLiteDither(3)
}
CanvasQuery.Wrapper.prototype.pattern4LiteDither = function() {
  this.patternLiteDither(4)
}
CanvasQuery.Wrapper.prototype.patternLiteDither = function(n) {
  var bitmap = this.context.getImageData(0, 0, this.canvas.width, this.canvas.height)
  var bitmapData = bitmap.data

  var width = this.canvas.width
  var height = this.canvas.height

  var pat = patterns[n]
  var len = pat.length

	for (var i = 0; i < height; i++) {
		for (var j = 0; j < width; j++) {
      var p = ((i % n) * n) + (j % n)
			var a = 4 * (i*width + j)
			var val = (bitmapData[a] + bitmapData[a+1] + bitmapData[a+2]) / (3*255)
      var lum = val > pat[p]/len ? 255 : 0
			bitmapData[a] = bitmapData[a+1] = bitmapData[a+2] = lum
    }
  }
  this.context.putImageData(bitmap, 0, 0);
  return this;
}

CanvasQuery.Wrapper.prototype.floydSteinbergDither = function(n) {
  var bitmap = this.context.getImageData(0, 0, this.canvas.width, this.canvas.height)
  var bitmapData = bitmap.data

  var mask = this.grayscaleToMask()

  var width = this.canvas.width
  var height = this.canvas.height

	for (var y = 0; y < height; y++) {
		for (var x = 0; x < width; x++) {
			var p = (y*width + x)
			var a = 4 * p
			var val = mask[p]
      var lum = val > 127 ? 255 : 0
      var error = val - lum
      if (x < width-1)
        mask[ (y*width) + x+1 ]     += 7/16 * error
      if (y < height-1 && x > 0)
        mask[ ((y+1)*width) + x-1 ] += 5/16 * error
      if (y < height-1)
        mask[ ((y+1)*width) + x ]   += 3/16 * error
      if (y < height-1 && x < width-1)
        mask[ ((y+1)*width) + x+1 ] += 1/16 * error
			bitmapData[a] = bitmapData[a+1] = bitmapData[a+2] = lum
    }
  }
  this.context.putImageData(bitmap, 0, 0);
  return this;
}

CanvasQuery.Wrapper.prototype.rightDither = function(n) {
  var bitmap = this.context.getImageData(0, 0, this.canvas.width, this.canvas.height)
  var bitmapData = bitmap.data

  var mask = this.grayscaleToMask()

  var width = this.canvas.width
  var height = this.canvas.height

	for (var y = 0; y < height; y++) {
		for (var x = 0; x < width; x++) {
			var p = (y*width + x)
			var a = 4 * p
			var val = mask[p]
      var lum = val > 127 ? 255 : 0
      var error = val - lum
      if (x < width-1)
        mask[ (y*width) + x+1 ]     += 7/16 * error
			bitmapData[a] = bitmapData[a+1] = bitmapData[a+2] = lum
    }
  }
  this.context.putImageData(bitmap, 0, 0);
  return this;
}

CanvasQuery.Wrapper.prototype.halftone = function(radius, angle) {
  var mask = this.grayscaleToMask()

  this.fillStyle("#fff")
  this.fillRect(0, 0, this.canvas.width, this.canvas.height)

  var diameter = radius*2
  var TWO_PI = Math.PI*2

  var angle = angle / 180 * Math.PI

  var cos = Math.cos(angle)
  var sin = Math.sin(angle)

  var xstep = cos * radius
  var ystep = sin * radius

  var w = this.canvas.width
  var h = this.canvas.height

  this.fillStyle("#000")

  for (var i = -w; i < w; i++) {
    for (var j = -h; j < h; j++) {
      var x = i * ystep - j * xstep
      var y = i * xstep + j * ystep
      if (x > -diameter && y > -diameter && x < w+diameter && y < h+diameter) {
        circle(this,x,y)
      }
    }
  }

  function circle(cq,x,y) {
    var xx = x < 0 ? 0 : x > w ? w - 1 : x;
    var yy = y < 0 ? 0 : y > h ? h - 1 : y;
		var r = (1 - Math.pow( mask[ ~~(~~yy*w+(xx)) ] / 255, Math.E/4 )) * radius
    cq.beginPath()
      .arc(x,y,r,0,TWO_PI)
      .closePath()
      .fill();
  }
  return this;
}