Use Core Graphics to draw an arc with a gradient fill, a stroked outline, and a shadow. http://stackoverflow.com/questions/15866179/draw-segments-from-a-circle-or-donut

drawArc.m

static UIImage *imageWithSize(CGSize size) {
    static CGFloat const kThickness = 20;
    static CGFloat const kLineWidth = 1;
    static CGFloat const kShadowWidth = 8;

    UIGraphicsBeginImageContextWithOptions(size, NO, 0); {
        CGContextRef gc = UIGraphicsGetCurrentContext();
        CGContextAddArc(gc, size.width / 2, size.height / 2,
            (size.width - kThickness - kLineWidth) / 2,
            -M_PI / 4, -3 * M_PI / 4, YES);
        CGContextSetLineWidth(gc, kThickness);
        CGContextSetLineCap(gc, kCGLineCapButt);
        CGContextReplacePathWithStrokedPath(gc);
        CGPathRef path = CGContextCopyPath(gc);

        CGContextSetShadowWithColor(gc,
            CGSizeMake(0, kShadowWidth / 2), kShadowWidth / 2,
            [UIColor colorWithWhite:0 alpha:0.3].CGColor);
        CGContextBeginTransparencyLayer(gc, 0); {

            CGContextSaveGState(gc); {
                CGColorSpaceRef rgb = CGColorSpaceCreateDeviceRGB();
                CGGradientRef gradient = CGGradientCreateWithColors(rgb, (__bridge CFArrayRef)@[
                    (__bridge id)[UIColor grayColor].CGColor,
                    (__bridge id)[UIColor whiteColor].CGColor
                ], (CGFloat[]){ 0.0f, 1.0f });
                CGColorSpaceRelease(rgb);

                CGRect bbox = CGContextGetPathBoundingBox(gc);
                CGPoint start = bbox.origin;
                CGPoint end = CGPointMake(CGRectGetMaxX(bbox), CGRectGetMaxY(bbox));
                if (bbox.size.width > bbox.size.height) {
                    end.y = start.y;
                } else {
                    end.x = start.x;
                }

                CGContextClip(gc);
                CGContextDrawLinearGradient(gc, gradient, start, end, 0);
                CGGradientRelease(gradient);
            } CGContextRestoreGState(gc);

            CGContextAddPath(gc, path);
            CGPathRelease(path);

            CGContextSetLineWidth(gc, kLineWidth);
            CGContextSetLineJoin(gc, kCGLineJoinMiter);
            [[UIColor blackColor] setStroke];
            CGContextStrokePath(gc);

        } CGContextEndTransparencyLayer(gc);
    }
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return image;
}