anchor.diff:      this.height: 400,
       List<Color> colors,
       this.onClick}) :
  -      colors = colors == null ? defaultColors : _makeCssColors(colors)
  +      this.colors = (colors == null) ? defaultColors : colors
     {
       var radiusPixels = width < height ? width/2.0 : height/2.0;
       scalePixel = radius / radiusPixels;
  
positive.code: 
    void draw(CanvasRenderingContext2D context) {
      var startTime = window.performance.now();
      //window.console.profile("draw");
      //var pixels = context.getImageData(0,  0,  width, height);
      for (int y = 0; y < height; y++) {
        drawLine(context, y);
      }
      //window.console.profileEnd("draw");
      var elapsedTime = window.performance.now() - startTime;
      print("draw time: ${elapsedTime} ms");
    }
  
    void drawLine(CanvasRenderingContext2D context, int y) {
      num imag = - pixelToCoordY(y);
  
      int left = null;
      String prevColor = null;
      int maxIterations = colors.length - 1;
      for (int x = 0; x < width; x++) {
        num real = pixelToCoordX(x);
        int count = probe(real, imag, maxIterations);
        String color = colors[count];
        //int pixel = (y * data.width + x) * 4;
        if (color != prevColor) {
          if (prevColor != null) {
            context.fillStyle = prevColor;
            context.fillRect(left, y, x - left, 1);
          }
          prevColor = color;
          left = x;
        }
      }
      context.fillStyle = prevColor;
      context.fillRect(left, y, width - left, 1);
    }
  
    num pixelToCoordX(int x) => scalePixel * (x - width / 2) + center.real;
    num pixelToCoordY(int y) => -scalePixel * (y - height / 2) + center.imag;
  
    static final List<String> defaultColors = _makeCssColors(colorRange(
        new HslColor(1, 80, 70),
        new HslColor(360 * 10, 100, 0),
        1000));
  
    static _makeCssColors(List<Color> input) =>
        input.map((c) => c.toCss()).toList()..add("#000");
  
negative.code:   final int width;
    final int height;
    final ClickHandler onClick;
    final List<Color> colors;
    double scalePixel;
  
    MandelbrotView({
  