<

  parameters: <

    xcenter: <

      label: "Center x";

      type: float;

    >;

    ycenter: <

      label: "Center y";

      type: float;

    >;

    radius: <

      label: "Radius";

      type:float;

      defaultValue: 0.1;

    >;

    ringradius: <

      label: "Ring radius";

      type:float;

      defaultValue: 0.05;

    >;

    outsidecolor: <

      label: "Outside color";

      type: rgba;

      defaultValue: { 0.0, 0.0, 0.0, 1.0 };

    >;                                                                        

    ballcolor: <

      label: "Ball color";

      type: rgba;

      defaultValue: { 0.0, 1.0, 0.0, 1.0 };

    >;                                                                        

  >;

>;

kernel Singleball

{

  const float2 center = { IMAGE_WIDTH * xcenter, IMAGE_HEIGHT * ycenter };

  dependent float pxradius, pxringradius;

  void evaluateDependents()

  {

    int image_size = min(IMAGE_WIDTH, IMAGE_HEIGHT);

    pxradius = radius * image_size;

    pxringradius = ringradius * image_size;

  }

  void evaluatePixel(out pixel4 result)

  {

    float2 vec = result.coord - center;

    float angle = atan2( vec.x, vec.y);

    float r = length(vec);

    if(r < pxradius or r > (pxradius + pxringradius))

    {

      result = outsidecolor;

    } else {

      float v = (r - pxradius) / pxringradius;

      result = (1.0 - v) * ballcolor + v * outsidecolor;

    }

  }

  region generated()

  {

    region reg = { 0, 0, IMAGE_WIDTH, IMAGE_HEIGHT};

    return reg;

  }

}