<

  parameters: <

    metaballs: <

      label: "Number of metaballs";

      type: int;

    >;

    radius: <

      label: "Radius";

      type:float;

      defaultValue: 0.05;

    >;

    ringradius: <

      label: "Ring radius";

      type:float;

      defaultValue: 0.03;

    >;

    outsidecolor: <

      label: "Outside color";

      type: rgba;

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

    >;                                                                        

    metaballcolor: <

      label: "Metaball color";

      type: rgba;

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

    >;                                                                        

  >;

>;

kernel Metaball

{

  dependent float2 centers[ metaballs ];

  dependent float pxradius, pxringradius;

  void evaluateDependents()

  {

    int image_size = min(IMAGE_WIDTH, IMAGE_HEIGHT);

    pxradius = radius * image_size;

    pxringradius = ringradius * image_size;

    const float RAND_MAX  = 2147483647;

    for(int i = 0; i < metaballs; ++i)

    {

      centers[i].x = rand() / RAND_MAX * IMAGE_WIDTH;

      centers[i].y = rand() / RAND_MAX * IMAGE_HEIGHT;

    }

  }

  void evaluatePixel(out pixel4 result)

  {

    result = outsidecolor;

    float maxv = 1.1;

    for(int i = 0; i < metaballs; ++i)

    {

      float2 vec = result.coord - centers[i];

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

      float r = length(vec);

      if(r < pxradius )

      {

        result = outsidecolor;

        i = metaballs;

      } else if( r < (pxradius + pxringradius)) {

        float v = (r - pxradius) / pxringradius;

        if(v < maxv)

        {

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

          maxv = v;

        }

      }

    }

  }

  region generated()

  {

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

    return reg;

  }

}