gistfile1.m

-(void)drawRect:(CGRect)rect {
    CGFloat side = MIN(self.bounds.size.width, self.bounds.size.height);

    NSInteger steps = 512;

    float internalRadius = side * 0.0;
    float externalRadius = side * 0.5;

    float halfinteriorPerim = M_PI * internalRadius;
    float halfexteriorPerim = M_PI * externalRadius;

    float smallBase= halfinteriorPerim / steps;
    float largeBase= halfexteriorPerim / steps;

    UIBezierPath *cell = [UIBezierPath bezierPath];

    [cell moveToPoint:CGPointMake(- smallBase/2, internalRadius)];
    [cell addLineToPoint:CGPointMake(+ smallBase/2, internalRadius)];

    [cell addLineToPoint:CGPointMake( largeBase /2 , externalRadius)];
    [cell addLineToPoint:CGPointMake(-largeBase /2,  externalRadius)];
    [cell closePath];

    float incr = 2 * M_PI / steps;
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    CGContextTranslateCTM(ctx, +self.bounds.size.width / 2, +self.bounds.size.height / 2);

    CGContextScaleCTM(ctx, 0.9, 0.9);
    CGContextRotateCTM(ctx, M_PI / 2);
    CGContextRotateCTM(ctx, -incr / 2);

    for (NSInteger index = 0; index < steps; index++) {
        [[UIColor colorWithHue:(float) index / steps
                   saturation:1.0
                   brightness:1.0
                        alpha:1.0] set];

        [cell fill];
        [cell stroke];

        CGContextRotateCTM(ctx, -incr);
    }
}