Smoothing Core Graphics curves

Question

I'm trying to create a circular loading bar and want to use Core Graphics instead of masking images to create the effect. However, I'm not getting the fidelity that I was hoping for:

No matter what have I've tried, the jaggies seem pretty bad. Antialiasing is on and I've already tried turning the "flatness" down to .1 on the CGContextRef. The image is from the (Retina) simulator, it looks slightly better on a device but still isn't that great.

Drawing code, within a subclass of CALayer:

-(void)drawInContext:(CGContextRef)ctx {    
    CGPoint center = CGPointMake(self.frame.size.width / 2, self.frame.size.height / 2);

    CGFloat delta = toRadians(360 * percent);

    CGFloat innerRadius = 69.5;
    CGFloat outerRadius = innerRadius + 12;

    CGContextSetFillColorWithColor(ctx, [UIColor colorWithRed:99/256.0 green:183/256.0 blue:70/256.0 alpha:.5].CGColor);
    CGContextSetStrokeColorWithColor(ctx, [UIColor colorWithRed:99/256.0 green:183/256.0 blue:70/256.0 alpha:10.0].CGColor);
    CGContextSetLineWidth(ctx, 1);

    CGMutablePathRef path = CGPathCreateMutable();

    CGPathAddRelativeArc(path, NULL, center.x, center.y, innerRadius, -(M_PI / 2), delta);
    CGPathAddRelativeArc(path, NULL, center.x, center.y, outerRadius, delta - (M_PI / 2), -delta);
    CGPathAddLineToPoint(path, NULL, center.x, center.y-innerRadius);

    CGContextAddPath(ctx, path);
    CGContextFillPath(ctx);
    CGContextAddPath(ctx, path);
    CGContextStrokePath(ctx);
}

Is this the best Core Graphics can do or am I missing something?

Answer 1

Found out my specific problem. Since I was creating a CALayer (to add as a sublayer) the contentScale was not automatically getting set to a Retina display. This solves it:

percentLayer.contentsScale = [UIScreen mainScreen].scale;

Thanks Rob, for pushing me in the right direction.