截屏、图片裁剪、拼接

我们在开发中经常需要使用截屏功能或者把某个view生成一张图片的功能，还有可能需要拼接在一起组成一张大图，另外有可能给一张大图添加水印图等。

屏幕截图

屏幕截图和view截成图一样，只是把对应的view换成window就行，示例代码如下

    UIGraphicsBeginImageContextWithOptions([UIApplication sharedApplication].keyWindow.bounds.size, NO, 0.0);
    CGContextRef context = UIGraphicsGetCurrentContext();
    [[UIApplication sharedApplication].keyWindow .layer renderInContext:context];
    UIImage *image= UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

这样截图出来的图片没有顶部状态栏，因为状态栏并不在keyWindow对应的view上，所以我们要加上相应的UIStatueBar

    UIGraphicsBeginImageContextWithOptions([UIApplication sharedApplication].keyWindow.bounds.size, NO, 0.0);
    CGContextRef context = UIGraphicsGetCurrentContext();
    [[UIApplication sharedApplication].keyWindow .layer renderInContext:context];
    //添加顶部状态栏
    UIView *statusBarView = [[[UIApplication sharedApplication] valueForKey:@"statusBarWindow"] valueForKey:@"statusBar"];
    [statusBarView.layer renderInContext:context];
    UIImage *image= UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

获取顶部状态栏View的方法OTScreenshotHelper中用的是runtime，也是可以获取到，有兴趣的同学可以去看下https://github.com/OpenFibers/OTScreenshotHelper
以上方法还有一个问题，就是对于有UIPickerView在页面上，PickView会有黑边，所以我们要把renderInContext替换成drawViewHierarchyInRect，示例代码如下

    UIGraphicsBeginImageContextWithOptions([UIApplication sharedApplication].keyWindow.bounds.size, NO, 0.0);
    CGContextRef context = UIGraphicsGetCurrentContext();
    [[UIApplication sharedApplication].keyWindow drawViewHierarchyInRect:(CGRect){.origin=CGPointZero, .size=[UIApplication sharedApplication].keyWindow.bounds.size} afterScreenUpdates:YES];
    //添加顶部状态栏
    UIView *statusBarView = [[[UIApplication sharedApplication] valueForKey:@"statusBarWindow"] valueForKey:@"statusBar"];
    [statusBarView.layer renderInContext:context];
    UIImage *image= UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

UIScrollView图片裁剪

一般的view的生成图片和上面截屏方法类似，而且可以不考虑顶部状态栏。对于UIScrollView用上面的方法获取的图片也是我们可见的，如果我们想要获取整个ContentSize的图片，对于UITableView和UICollectionView往往会留下一片空白部分，达不到我们想要的效果。要达到整个都截取的话，我们可以分段截图，然后拼接，也可以改变其frame，让所有cell都渲染出来。

- (UIImage *)screenshotImageWithScrollView:(UIScrollView *)scrollView
                                imageSize:(CGSize)size{
    CGPoint orignalContentOffset = scrollView.contentOffset;
    CGRect orignalFrame = scrollView.frame;
    
    UIScrollView *rt = scrollView;
    CGRect frm = scrollView.frame;
    frm.size.height = size.height;
    rt.frame = frm;
    
    UIGraphicsBeginImageContextWithOptions(size, NO, 0.0);
    CGContextRef context = UIGraphicsGetCurrentContext();
    [rt.layer renderInContext:context];
    UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    scrollView.contentOffset = orignalContentOffset;
    scrollView.frame = orignalFrame;
    return viewImage;
}

上面就是改变ScrollView的frame，高度和contentSize的height一样，等截图才做完成后重新回到它原状态。裁剪ScrollView生成图片的尺寸和我们给的尺寸有变差，需要注意生成图片的scale，裁剪示例代码如下

    UIImage *screenImg = [self screenshotImageWithScrollView:scrollView imageSize:scrollView.contentSize];
    CGImageRef screenImageRef = screenImg.CGImage;
    CGImageRef rectImageRef = CGImageCreateWithImageInRect(screenImageRef, CGRectMake(rect.origin.x*screenImg.scale, rect.origin.y*screenImg.scale, rect.size.width*screenImg.scale, rect.size.height*screenImg.scale));
    UIImage* rectImage = [UIImage imageWithCGImage:rectImageRef];
    CGImageRelease(rectImageRef);

图片添加水印

图片拼接、添加水印都基本一样，都在画布中画出图片

- (UIImage *)imageAddMaskWithImage:(UIImage *)orignalImage
                         imageSize:(CGSize)imageSize
                         maskImage:(UIImage *)maskImage
                     maskImageRect:(CGRect)maskRect
                         maskAlpha:(CGFloat)maskAlpha{
    UIGraphicsBeginImageContextWithOptions(imageSize, NO, 0.0);
    [orignalImage drawInRect:CGRectMake(0, 0, imageSize.width, imageSize.height)];
    [maskImage drawInRect:maskRect blendMode:kCGBlendModeNormal alpha:maskAlpha];
    UIImage *resultingImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return resultingImage;
}

总结

以上都是静态页面的截图，对于正在执行动画的页面没测试，有兴趣的同学可以尝试一下。另外对于WebView上述方式是截取不了整个WebView,这有个解决方法https://www.jianshu.com/p/ef50defb979d,最后附上demoOC、Swift。