addArc method
Adds a new sub-path 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);
}