IrregularShadow.m

/**
 * 使用UIKit方式生成路径
 */
///////////////////////////////////////////////////////////////////////////////////////////////////
- (CGPathRef)renderPaperCurl:(UIView*)imgView {
    CGSize size = imgView.bounds.size;
    CGFloat curlFactor = 12.0f;
    CGFloat shadowDepth = 4.0f;
  CGFloat translationFactor = 6.0f;
    UIBezierPath *path = [UIBezierPath bezierPath];
    [path moveToPoint:CGPointMake(0.0f + translationFactor, 0.0f)];
    [path addLineToPoint:CGPointMake(size.width - translationFactor, 0.0f)];
    [path addLineToPoint:CGPointMake(size.width - translationFactor, size.height + shadowDepth)];
    [path addCurveToPoint:CGPointMake(0.0f + translationFactor, size.height + shadowDepth)
            controlPoint1:CGPointMake(size.width - translationFactor - curlFactor, size.height + shadowDepth - curlFactor)
            controlPoint2:CGPointMake(curlFactor + translationFactor, size.height + shadowDepth - curlFactor)];

    return path.CGPath;
}


/**
 * 使用Quartz方式生成路径
 */
///////////////////////////////////////////////////////////////////////////////////////////////////
- (CGPathRef)renderPaperCurlPathUsingQuartz:(UIView*)imgView {
    CGSize size = imgView.bounds.size;
    CGFloat curlFactor = 12.0f;
    CGFloat shadowDepth = 4.0f;
  CGFloat translationFactor = 6.0f;
  
  CGMutablePathRef path = CGPathCreateMutable();
  CGPathMoveToPoint(path, NULL, 0.0 + translationFactor, 0.0f);
  CGPathAddLineToPoint(path, NULL, size.width - translationFactor, 0.0f);
  CGPathAddLineToPoint(path, NULL, size.width - translationFactor, size.height + shadowDepth);
  CGPathAddCurveToPoint(path, NULL,
                        size.width - translationFactor - curlFactor, size.height + shadowDepth - curlFactor,
                        curlFactor + translationFactor, size.height + shadowDepth - curlFactor,
                        0.0f + translationFactor, size.height + shadowDepth);
  
  return path;
}


- (void)loadView {
  [super loadView];
  self.view.backgroundColor = [UIColor colorWithRed:242.0/255.0f green:232/255.0f blue:225/255.0f alpha:1];
  UIImage *image = [UIImage imageNamed:@"dccp.jpeg"];
  UIImageView *imgView = [[UIImageView alloc] initWithImage:image];
  [self.view addSubview:imgView];
  imgView.center = self.view.center;
  imgView.layer.borderWidth = 4;
  imgView.layer.borderColor = [UIColor whiteColor].CGColor;
  imgView.layer.shadowColor = [UIColor blackColor].CGColor;
  imgView.layer.shadowOpacity = 0.6f;
  imgView.layer.shadowOffset = CGSizeMake(0.0f, 4.0f);
  imgView.layer.shadowRadius = 1.0f;
  imgView.layer.masksToBounds = NO;

  imgView.layer.shadowPath = [self renderPaperCurl:imgView];
/*
  CGPathRef path = [self renderPaperCurlPathUsingQuartz:imgView];
  imgView.layer.shadowPath = path;
  CFRelease(path);
*/
}