addArc method

void addArc (Rect oval, double startAngle, double sweepAngle)

Adds a new subpath with one arc segment that consists of the arc that follows the edge of the oval bounded by the given rectangle, from startAngle radians around the oval up to startAngle + sweepAngle radians around the oval, with zero radians being the point on the right hand side of the oval that crosses the horizontal line that intersects the center of the rectangle and with positive angles going clockwise around the oval.

Implementation 

void addArc(Rect oval, double startAngle, double sweepAngle) {
  assert(_rectIsValid(oval));
  _addArc(oval.left, oval.top, oval.right, oval.bottom, startAngle, sweepAngle);
}