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
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;
}
其他回答
在Swift中裁剪UIImage的最佳解决方案，在精度方面，像素缩放…:
private func squareCropImageToSideLength(let sourceImage: UIImage,
let sideLength: CGFloat) -> UIImage {
// input size comes from image
let inputSize: CGSize = sourceImage.size
// round up side length to avoid fractional output size
let sideLength: CGFloat = ceil(sideLength)
// output size has sideLength for both dimensions
let outputSize: CGSize = CGSizeMake(sideLength, sideLength)
// calculate scale so that smaller dimension fits sideLength
let scale: CGFloat = max(sideLength / inputSize.width,
sideLength / inputSize.height)
// scaling the image with this scale results in this output size
let scaledInputSize: CGSize = CGSizeMake(inputSize.width * scale,
inputSize.height * scale)
// determine point in center of "canvas"
let center: CGPoint = CGPointMake(outputSize.width/2.0,
outputSize.height/2.0)
// calculate drawing rect relative to output Size
let outputRect: CGRect = CGRectMake(center.x - scaledInputSize.width/2.0,
center.y - scaledInputSize.height/2.0,
scaledInputSize.width,
scaledInputSize.height)
// begin a new bitmap context, scale 0 takes display scale
UIGraphicsBeginImageContextWithOptions(outputSize, true, 0)
// optional: set the interpolation quality.
// For this you need to grab the underlying CGContext
let ctx: CGContextRef = UIGraphicsGetCurrentContext()
CGContextSetInterpolationQuality(ctx, kCGInterpolationHigh)
// draw the source image into the calculated rect
sourceImage.drawInRect(outputRect)
// create new image from bitmap context
let outImage: UIImage = UIGraphicsGetImageFromCurrentImageContext()
// clean up
UIGraphicsEndImageContext()
// pass back new image
return outImage
}
调用此函数的指令:
let image: UIImage = UIImage(named: "Image.jpg")!
let squareImage: UIImage = self.squareCropImageToSideLength(image, sideLength: 320)
self.myUIImageView.image = squareImage
注意:最初的源代码灵感是用Objective-C写的，可以在Cocoanetics博客上找到。
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;
}
在iOS9.2SDK上，我使用下面的方法将帧从UIView转换为UIImage
-(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;
}
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;
}
