【iOS】正多角形を描く - UIBezierPathバージョン2

こないだのだとなんか傾いてるので。

- (void)drawRegularPolygon:(NSUInteger)p radius:(CGFloat)radius center:(CGPoint)center
{
    UIBezierPath *aPath = [UIBezierPath bezierPath];
    aPath.lineWidth = 1;
    for (NSInteger i = 0; i < p; i++) {
        double rad = M_PI * i * 2 / p + M_PI_2;
        CGPoint drawPoint = CGPointMake(center.x + radius * cos(rad), center.y - radius * sin(rad));
        if (i == 0)
            [aPath moveToPoint:drawPoint];
        else
            [aPath addLineToPoint:drawPoint];
    }
    [aPath closePath];
    [[UIColor redColor] setStroke];
    [aPath stroke];
}