裁剪UIImage屏幕截图

Question

我目前正在替换代码中的UIGetScreenImage（），因为它会导致C99错误。

我将用苹果的这段代码替换它，screenshot方法返回一个UIImage。

我尝试裁剪和保存图像如下：

UIImage *returnedImage = [self screenshot];
// Get image to save
CGImageRef screen = returnedImage.CGImage;
UIImage *img = [UIImage imageWithCGImage:screen];
// Image cropping
CGImageRef imageRef = CGImageCreateWithImageInRect([img CGImage], CGRectMake(0, 5, 768, 1004));
UIImage *img2Save = [UIImage imageWithCGImage:imageRef];
CGImageRelease(imageRef);
// Request to save the image to camera roll
UIImageWriteToSavedPhotosAlbum(img2Save, self, nil, nil);

在返回之前，我也尝试过在screenshot方法中裁剪它，但没有成功。

通过两次尝试，保存从screenshot方法返回的未阻塞的UIImage。

我有什么明显遗漏的吗？我看了这个SO线程，但看不到连接。

Answer 1

请尝试以下代码

- (UIImage*)imageByCropping:(UIImage *)imageToCrop toRect:(CGRect)rect
{
   //create a context to do our clipping in
   UIGraphicsBeginImageContext(rect.size);
   CGContextRef currentContext = UIGraphicsGetCurrentContext();
   //create a rect with the size we want to crop the image to
   //the X and Y here are zero so we start at the beginning of our
   //newly created context
   CGRect clippedRect = CGRectMake(0, 0, rect.size.width, rect.size.height);
   CGContextClipToRect( currentContext, clippedRect);
   //create a rect equivalent to the full size of the image
   //offset the rect by the X and Y we want to start the crop
   //from in order to cut off anything before them
   CGRect drawRect = CGRectMake(rect.origin.x * -1,
                                rect.origin.y * -1,
                                imageToCrop.size.width,
                                imageToCrop.size.height);
   //draw the image to our clipped context using our offset rect
   CGContextDrawImage(currentContext, drawRect, imageToCrop.CGImage);
   //pull the image from our cropped context
   UIImage *cropped = UIGraphicsGetImageFromCurrentImageContext();
   //pop the context to get back to the default
   UIGraphicsEndImageContext();
   //Note: this is autoreleased
   return cropped;
}

然后用类似的东西调用代码：

- (void)drawRect:(CGRect)rect
{
   //draw the whole lights off image
   //the on images will be drawn overtop
   [lightsOffImage drawInRect:rect];
   //if we don't have any lights on... no point in continuing
   if( numberOfLightsOn < 1 )
     return;
   //figure out the dimensions of numberOfLights on bulbs
   CGSize croppedSize = CGSizeMake(LIGHT_WIDTH * numberOfLightsOn, LIGHT_HEIGHT);
   CGRect clippedRect = CGRectMake(0, 0, croppedSize.width, croppedSize.height);
   //get the "on" bulbs by cropping the image
   UIImage *cropped = [self imageByCropping:lightsOnImage toRect:clippedRect];
   //create a rect to draw the newly cropped on images to
   CGRect lightsOnRect = CGRectMake(LIGHT_BULB_OFFSET_X,
                                    LIGHT_BULB_OFFSET_Y,
                                    croppedSize.width,
                                    croppedSize.height);
   //draw the "on" lights
   [cropped drawInRect:lightsOnRect];
   //cropped is autoreleased so no need to worry about cleanup
}

愿此代码对您有所帮助。