code: func (imd *IMDraw) CircleArc(radius, low, high, thickness float64) {
  	if thickness == 0 {
  		imd.fillEllipseArc(pixel.V(radius, radius), low, high)
  	} else {
  		imd.outlineEllipseArc(pixel.V(radius, radius), low, high, thickness, true)
  	}
  }
docs: // CircleArc draws a circle arc of the specified radius around each Pushed point. If the thickness
  // is 0, the arc will be filled, otherwise will be outlined. The arc starts at the low angle and
  // continues to the high angle. If low<high, the arc will be drawn counterclockwise. Otherwise it
  // will be clockwise. The angles are not normalized by any means.
  //
  //   imd.CircleArc(40, 0, 8*math.Pi, 0)
  //
  // This line will fill the whole circle 4 times.