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
迅速扩展
extension UIImage {
func crop(var rect: CGRect) -> UIImage {
rect.origin.x*=self.scale
rect.origin.y*=self.scale
rect.size.width*=self.scale
rect.size.height*=self.scale
let imageRef = CGImageCreateWithImageInRect(self.CGImage, rect)
let image = UIImage(CGImage: imageRef, scale: self.scale, orientation: self.imageOrientation)!
return image
}
}
其他回答
这是我的UIImage作物实现，它遵从imageOrientation属性。所有方向都经过了彻底的测试。
inline double rad(double deg)
{
return deg / 180.0 * M_PI;
}
UIImage* UIImageCrop(UIImage* img, CGRect rect)
{
CGAffineTransform rectTransform;
switch (img.imageOrientation)
{
case UIImageOrientationLeft:
rectTransform = CGAffineTransformTranslate(CGAffineTransformMakeRotation(rad(90)), 0, -img.size.height);
break;
case UIImageOrientationRight:
rectTransform = CGAffineTransformTranslate(CGAffineTransformMakeRotation(rad(-90)), -img.size.width, 0);
break;
case UIImageOrientationDown:
rectTransform = CGAffineTransformTranslate(CGAffineTransformMakeRotation(rad(-180)), -img.size.width, -img.size.height);
break;
default:
rectTransform = CGAffineTransformIdentity;
};
rectTransform = CGAffineTransformScale(rectTransform, img.scale, img.scale);
CGImageRef imageRef = CGImageCreateWithImageInRect([img CGImage], CGRectApplyAffineTransform(rect, rectTransform));
UIImage *result = [UIImage imageWithCGImage:imageRef scale:img.scale orientation:img.imageOrientation];
CGImageRelease(imageRef);
return result;
}
你可以创建一个UIImage类别，并在任何你需要的地方使用它。基于HitScans的响应和咆哮的评论。
@implementation UIImage (Crop)
- (UIImage *)crop:(CGRect)rect {
rect = CGRectMake(rect.origin.x*self.scale,
rect.origin.y*self.scale,
rect.size.width*self.scale,
rect.size.height*self.scale);
CGImageRef imageRef = CGImageCreateWithImageInRect([self CGImage], rect);
UIImage *result = [UIImage imageWithCGImage:imageRef
scale:self.scale
orientation:self.imageOrientation];
CGImageRelease(imageRef);
return result;
}
@end
你可以这样用:
UIImage *imageToCrop = <yourImageToCrop>;
CGRect cropRect = <areaYouWantToCrop>;
//for example
//CGRectMake(0, 40, 320, 100);
UIImage *croppedImage = [imageToCrop crop:cropRect];
Swift 3版本
func cropImage(imageToCrop:UIImage, toRect rect:CGRect) -> UIImage{
let imageRef:CGImage = imageToCrop.cgImage!.cropping(to: rect)!
let cropped:UIImage = UIImage(cgImage:imageRef)
return cropped
}
let imageTop:UIImage = UIImage(named:"one.jpg")! // add validation
在这个桥接函数CGRectMake -> CGRect的帮助下(这个答案由@rob mayoff回答):
func CGRectMake(_ x: CGFloat, _ y: CGFloat, _ width: CGFloat, _ height: CGFloat) -> CGRect {
return CGRect(x: x, y: y, width: width, height: height)
}
用法是:
if var image:UIImage = UIImage(named:"one.jpg"){
let croppedImage = cropImage(imageToCrop: image, toRect: CGRectMake(
image.size.width/4,
0,
image.size.width/2,
image.size.height)
)
}
输出:
swift3
extension UIImage {
func crop(rect: CGRect) -> UIImage? {
var scaledRect = rect
scaledRect.origin.x *= scale
scaledRect.origin.y *= scale
scaledRect.size.width *= scale
scaledRect.size.height *= scale
guard let imageRef: CGImage = cgImage?.cropping(to: scaledRect) else {
return nil
}
return UIImage(cgImage: imageRef, scale: scale, orientation: imageOrientation)
}
}
- (UIImage *)getSubImage:(CGRect) rect{
CGImageRef subImageRef = CGImageCreateWithImageInRect(self.CGImage, rect);
CGRect smallBounds = CGRectMake(rect.origin.x, rect.origin.y, CGImageGetWidth(subImageRef), CGImageGetHeight(subImageRef));
UIGraphicsBeginImageContext(smallBounds.size);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextDrawImage(context, smallBounds, subImageRef);
UIImage* smallImg = [UIImage imageWithCGImage:subImageRef];
UIGraphicsEndImageContext();
return smallImg;
}
