ios - 按角度旋转 UIImageView

Question

我想通过按下按钮来旋转 UIImageView。我正在使用这段代码:

#import "UIImage-Extensions.h"
UIImage *rotatedImage = [SplashItGroupPicker.image imageRotatedByDegrees:360/arrayCount];
SplashItGroupPicker.image = rotatedImage;

在“UIImage-Extensions.h”中我有:

@interface UIImage (CS_Extensions)
- (UIImage *)imageRotatedByRadians:(CGFloat)radians;
- (UIImage *)imageRotatedByDegrees:(CGFloat)degrees;

在 .m 中:

- (UIImage *)imageRotatedByRadians:(CGFloat)radians
{
return [self imageRotatedByDegrees:RadiansToDegrees(radians)];
}

 - (UIImage *)imageRotatedByDegrees:(CGFloat)degrees
{
// calculate the size of the rotated view's containing box for our drawing space
UIView *rotatedViewBox = [[UIView alloc] initWithFrame:CGRectMake(0,0,self.size.width,     self.size.height)];
CGAffineTransform t = CGAffineTransformMakeRotation(DegreesToRadians(degrees));
rotatedViewBox.transform = t;
CGSize rotatedSize = rotatedViewBox.frame.size;

// Create the bitmap context
UIGraphicsBeginImageContext(rotatedSize);
CGContextRef bitmap = UIGraphicsGetCurrentContext();

// Move the origin to the middle of the image so we will rotate and scale around the center.
CGContextTranslateCTM(bitmap, rotatedSize.width/2, rotatedSize.height/2);

//   // Rotate the image context
CGContextRotateCTM(bitmap, DegreesToRadians(degrees));

// Now, draw the rotated/scaled image into the context
CGContextScaleCTM(bitmap, 1.0, -1.0);
CGContextDrawImage(bitmap, CGRectMake(-self.size.width / 2, -self.size.height / 2, self.size.width, self.size.height), [self CGImage]);

UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;

}

...旋转效果很好，但是当图像旋转时，图像也会变小，我不明白为什么。有什么想法吗？

Answer 1

猜测一下，这是否只发生在 Retina 屏幕上？每当从图形上下文中保存 UIImage 时，您需要确保比例正确。我是这样做的:

CGFloat scale = [[UIScreen mainScreen] scale];
CGSize size = CGSizeMake(rotatedViewBox.frame.size.width * scale, rotatedViewBox.frame.size.height * scale);

UIGraphicsBeginImageContext( size );

/* Do your image manipulations here */

UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

// overwrite the image with one that has the correct scale set
newImage = [UIImage imageWithCGImage:newImage.CGImage scale:scale orientation:newImage.imageOrientation];