我有一些代码来调整图像的大小，这样我就可以得到图像中心的缩放块-我用这个来获取一个UIImage，并返回一个小的，正方形的图像表示，类似于在照片应用程序的相册视图中看到的。(我知道我可以使用UIImageView和调整裁剪模式来实现相同的结果，但这些图像有时显示在UIWebViews中)。
我已经开始注意到这段代码中的一些崩溃，我有点难住了。我有两种不同的理论，不知道哪一种是正确的。
理论1)我通过绘制到目标尺寸的屏幕外图像上下文来实现裁剪。因为我想要图像的中心部分，所以我将传递给drawwinrect的CGRect参数设置为比图像上下文的边界更大的值。我希望这是符合规定的，但我是不是在试图掩盖其他我不应该触及的记忆?
理论2)我在后台线程中做所有这些。我知道UIKit的某些部分被限制在主线程中。我假设/希望绘制到屏幕外的视图不是其中之一。我错了吗?
(哦，我真怀念NSImage的drawwinrect:fromRect:operation:fraction:方法。)
当前回答
以下是基于面条回答的Swift 3更新版本
func cropping(to rect: CGRect) -> UIImage? {
if let cgCrop = cgImage?.cropping(to: rect) {
return UIImage(cgImage: cgCrop)
}
else if let ciCrop = ciImage?.cropping(to: rect) {
return UIImage(ciImage: ciCrop)
}
return nil
}
其他回答
我使用下面的方法。
-(UIImage *)getNeedImageFrom:(UIImage*)image cropRect:(CGRect)rect
{
CGSize cropSize = rect.size;
CGFloat widthScale =
image.size.width/self.imageViewOriginal.bounds.size.width;
CGFloat heightScale =
image.size.height/self.imageViewOriginal.bounds.size.height;
cropSize = CGSizeMake(rect.size.width*widthScale,
rect.size.height*heightScale);
CGPoint pointCrop = CGPointMake(rect.origin.x*widthScale,
rect.origin.y*heightScale);
rect = CGRectMake(pointCrop.x, pointCrop.y, cropSize.width,
cropSize.height);
CGImageRef subImage = CGImageCreateWithImageInRect(image.CGImage, rect);
UIImage *croppedImage = [UIImage imageWithCGImage:subImage];
CGImageRelease(subImage);
return croppedImage;
}
看看https://github.com/vvbogdan/BVCropPhoto
- (UIImage *)croppedImage {
CGFloat scale = self.sourceImage.size.width / self.scrollView.contentSize.width;
UIImage *finalImage = nil;
CGRect targetFrame = CGRectMake((self.scrollView.contentInset.left + self.scrollView.contentOffset.x) * scale,
(self.scrollView.contentInset.top + self.scrollView.contentOffset.y) * scale,
self.cropSize.width * scale,
self.cropSize.height * scale);
CGImageRef contextImage = CGImageCreateWithImageInRect([[self imageWithRotation:self.sourceImage] CGImage], targetFrame);
if (contextImage != NULL) {
finalImage = [UIImage imageWithCGImage:contextImage
scale:self.sourceImage.scale
orientation:UIImageOrientationUp];
CGImageRelease(contextImage);
}
return finalImage;
}
- (UIImage *)imageWithRotation:(UIImage *)image {
if (image.imageOrientation == UIImageOrientationUp) return image;
CGAffineTransform transform = CGAffineTransformIdentity;
switch (image.imageOrientation) {
case UIImageOrientationDown:
case UIImageOrientationDownMirrored:
transform = CGAffineTransformTranslate(transform, image.size.width, image.size.height);
transform = CGAffineTransformRotate(transform, M_PI);
break;
case UIImageOrientationLeft:
case UIImageOrientationLeftMirrored:
transform = CGAffineTransformTranslate(transform, image.size.width, 0);
transform = CGAffineTransformRotate(transform, M_PI_2);
break;
case UIImageOrientationRight:
case UIImageOrientationRightMirrored:
transform = CGAffineTransformTranslate(transform, 0, image.size.height);
transform = CGAffineTransformRotate(transform, -M_PI_2);
break;
case UIImageOrientationUp:
case UIImageOrientationUpMirrored:
break;
}
switch (image.imageOrientation) {
case UIImageOrientationUpMirrored:
case UIImageOrientationDownMirrored:
transform = CGAffineTransformTranslate(transform, image.size.width, 0);
transform = CGAffineTransformScale(transform, -1, 1);
break;
case UIImageOrientationLeftMirrored:
case UIImageOrientationRightMirrored:
transform = CGAffineTransformTranslate(transform, image.size.height, 0);
transform = CGAffineTransformScale(transform, -1, 1);
break;
case UIImageOrientationUp:
case UIImageOrientationDown:
case UIImageOrientationLeft:
case UIImageOrientationRight:
break;
}
// Now we draw the underlying CGImage into a new context, applying the transform
// calculated above.
CGContextRef ctx = CGBitmapContextCreate(NULL, image.size.width, image.size.height,
CGImageGetBitsPerComponent(image.CGImage), 0,
CGImageGetColorSpace(image.CGImage),
CGImageGetBitmapInfo(image.CGImage));
CGContextConcatCTM(ctx, transform);
switch (image.imageOrientation) {
case UIImageOrientationLeft:
case UIImageOrientationLeftMirrored:
case UIImageOrientationRight:
case UIImageOrientationRightMirrored:
// Grr...
CGContextDrawImage(ctx, CGRectMake(0, 0, image.size.height, image.size.width), image.CGImage);
break;
default:
CGContextDrawImage(ctx, CGRectMake(0, 0, image.size.width, image.size.height), image.CGImage);
break;
}
// And now we just create a new UIImage from the drawing context
CGImageRef cgimg = CGBitmapContextCreateImage(ctx);
UIImage *img = [UIImage imageWithCGImage:cgimg];
CGContextRelease(ctx);
CGImageRelease(cgimg);
return img;
}
wolf回答的快速版本，对我来说很管用:
public extension UIImage {
func croppedImage(inRect rect: CGRect) -> UIImage {
let rad: (Double) -> CGFloat = { deg in
return CGFloat(deg / 180.0 * .pi)
}
var rectTransform: CGAffineTransform
switch imageOrientation {
case .left:
let rotation = CGAffineTransform(rotationAngle: rad(90))
rectTransform = rotation.translatedBy(x: 0, y: -size.height)
case .right:
let rotation = CGAffineTransform(rotationAngle: rad(-90))
rectTransform = rotation.translatedBy(x: -size.width, y: 0)
case .down:
let rotation = CGAffineTransform(rotationAngle: rad(-180))
rectTransform = rotation.translatedBy(x: -size.width, y: -size.height)
default:
rectTransform = .identity
}
rectTransform = rectTransform.scaledBy(x: scale, y: scale)
let transformedRect = rect.applying(rectTransform)
let imageRef = cgImage!.cropping(to: transformedRect)!
let result = UIImage(cgImage: imageRef, scale: scale, orientation: imageOrientation)
return result
}
}
Swift 5.0更新
public extension UIImage {
func cropped(rect: CGRect) -> UIImage? {
if let image = self.cgImage!.cropping(to: rect) {
return UIImage(cgImage: image)
} else if let image = (self.ciImage)?.cropped(to: rect) {
return UIImage(ciImage: image)
}
return nil
}
}
注意:所有这些答案都假设一个cgimage支持的图像对象。
的形象。CGImage可以返回nil，如果UIImage是由CIImage支持的，如果你用CIFilter创建了这个图像。
在这种情况下，您可能必须在新的上下文中绘制图像，并返回该图像(缓慢)。
UIImage* crop(UIImage *image, rect) {
UIGraphicsBeginImageContextWithOptions(rect.size, false, [image scale]);
[image drawAtPoint:CGPointMake(-rect.origin.x, -rect.origin.y)];
cropped_image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return cropped_image;
}
