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function _build_pie_chart($config, $chart) {
  /* polar coordinates */
  $theme = drawing_graph_color($config, $chart);
  $start = 0; //define a starting angle for the first slice
  $separation = 0.1; // this will be for exploded pie
  $r = min($config['height'], $config['width'])/2 - 20;
  $center = '0,0';
  foreach($chart['points'] as $points) {
    $sum += $points[1];
  }

  $L = _crd(_rad_to_crd($start, $r));
  $ang = 0;
  foreach($chart['points'] as $n => $points) {
    /* $points[0] is the label, $points[1] is the value*/
    $stepsize = $points[1]/$sum * 2 * M_PI; //angle of the slice

    if($stepsize > M_PI) { $longarc = 1; }
    else { $longarc = 0;}

    $ang += $stepsize; //to calculate the angle of the end of the arc
    /*$A = _crd(_rad_to_crd($ang - $separation, $r)); //end of the arc*/
    $A = _crd(_rad_to_crd($ang, $r)); //end of the arc

    /*$center = _crd(_rad_to_crd($ang - $stepsize/2, 10)); //for exploded pie*/

    $d[$n] = 'M ' . $center // move to the center (if we want to explode the pie, do here)
      . ' L ' . $L  // move to the start of the arc
      . ' A ' . $r . ',' . $r . ' 0 ' . $longarc . ',1 ' . $A //arc
      /*. ' A ' . $r . ',' . $r . ' 0 0,1 ' . $A //arc*/
      . ' Z'; // close the curve
    /*$L = _crd(_rad_to_crd($ang - $separation, $r)); //end of the arc*/
    $L = $A;

    $canvas['plot']['slice_'.$n] = array(
      '#type' => 'drawing_path',
      '#fill' => $theme[$n]['fill'],
      '#explicit' => TRUE,
      '#points' => $d[$n],
      '#opacity' => 0.5,
      );
    /* Label part */
    $dist = $config['labels']['inside'] ? 2/3 * $r : $r *1.1;
    $coordinates = _rad_to_crd($ang - $stepsize/2, $dist);
    $canvas['plot']['label_'.$n] = array(
      '#type' => 'drawing_text',
      '#value' => $points[0],
      '#cx' => $coordinates[0],
      '#cy' => $coordinates[1],
      '#stroke' => 'none',
    );
  }
  return $canvas;
}