一些有关图像处理的代码片段

捕捉屏幕截图
CALayer实例使用Core Graphics的renderInContext方法可以将视图绘制到图像上下文中以便转化为其他UIImage实例。前提先#import <QuartzCore/QuartzCore.h>

+ (UIImage *) imageFromView: (UIView *)theView {
    // draw a view's contents into an image context
   UIGraphicsBeginImageContext(theView.frame.size);
   CGContextRef  context = UIGraphicsGetCurrentContext();

   [theView.layer  renderInContext:context];
   UIImage *theImage = UIGraphicsGetImageFromCurrentImageContext();
   UIGraphicsEndImageContext(); 
   return theImage;
}

注：UIGraphicsBeginImageContext(CGSize size)创建一个基于位图的上下文(context)，并将其设置为当前上下文。函数功能与UIGraphicsBeginImageContextWithOptions相同，相当于该方法的opaque参数为NO，scale因子为1.0。而UIGraphicsEndImageContext()方法是移除栈顶的基于当前位图的图形上下文。

 

视图添加倒影效果

const CGFloat kReflectPercent = -0.25f;
const CGFloat kReflectOpacity = 0.3f;
const CGFloat kReflectDistance = 10.0f;

+ (void)addSimpleReflectionToView:(UIView *)theView
{
     CALayer *reflectionLayer = [CALayer layer];
     reflectionLayer.contents = [theView layer].contents;
     reflectionLayer.opacity = kReflectOpacity;
     reflectionLayer.frame = CGRectMake(0.0f,0.0f,theView.frame.size.width,theView.frame.size.height*kReflectPercent);  //倒影层框架设置，其中高度是原视图的百分比
    CATransform3D stransform = CATransform3DMakeScale(1.0f,-1.0f,1.0f);
     CATransform3D transform = CATransform3DTranslate(stransform,0.0f,-(kReflectDistance + theView.frame.size.height),0.0f);
     reflectionLayer.transform = transform;
     reflectionLayer.sublayerTransform = reflectionLayer.transform;
     [[theView layer] addSublayer:reflectionLayer];
}

 另一：使用Core Graphics创建倒影

+ (CGImageRef) createGradientImage:(CGSize)size
{
      CGFloat colors[] = {0.0,1.0,1.0,1.0};
      //在灰色设备色彩上建立一渐变
     CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();
      CGContextRef context = CGBitmapContextCreate(nil,size.width,size.height,8,0,colorSpace,kCGImageAlphaNone);
      CGGradientRef gradient = CGGradientCreateWithColorComponents(colorSpace,colors,NULL,2);
      CGColorSpaceRelease(colorSpace);

      //绘制线性渐变
     CGPoint p1 = CGPointZero;
      CGPoint p2 = CGPointMake(0,size.height);
      CGContextDrawLinearGradient(context,gradient,p1,p2,kCGGradientDrawsAfterEndLocation);

      //Return the CGImage
      CGImageRef theCGImage = CGBitmapContextCreateImage(context);
      CFRelease(gradient);
      CGContextRelease(context);
      return theCGImage;
}

//Create a shrunken frame for the reflection

+ (UIImage *) reflectionOfView:(UIView *)theView WithPercent:(CGFloat) percent
{
     //Retain the width but shrink the height
     CGSize size = CGSizeMake(theView.frame.size.width, theView.frame.size.height * percent);

     //Shrink the View
     UIGraphicsBeginImageContext(size);
     CGContextRef context = UIGraphicsGetCurrentContext();
     [theView.layer renderInContext:context];
     UIImage *partialimg = UIGraphicsGetImageFromCurrentImageContext();
     UIGraphicsEndImageContext();

     //ild the mask
     CGImageRef mask = [ImageHelper createGradientImage:size];
     CGImageRef ref = CGImageCreateWithMask(partialimg.CGImage,mask);
     UIImage *theImage = [UIImage imageWithCGImage:ref];
     CGImageRelease(ref);
     CGImageRelease(mask);
     return theImage;
}

const CGFloat kReflectDistance = 10.0f;
+ (void) addReflectionToView: (UIView *)theView
{
     theView.clipsToBounds = NO;
     UIImageView *reflection = [[UIImageView alloc] initWithImage:[ImageHelper reflectionOfView:theView withPercent:0.45f]];
     CGRect frame = reflection.frame;
     frame.origin = CGPointMake(0.0f, theView.frame.size.height + kReflectDistance);
     reflection.frame = frame;

     // add the reflection as a simple subview
     [theView addSubView:reflection];
     [reflection release];
}