Iphone 旋转UIImage可生成空白UIImage

我想使用此方法将UIImage旋转90度：

static inline double radians (double degrees) {return degrees * M_PI/180;}
UIImage* rotate(UIImage* src, UIImageOrientation orientation)
{
    UIGraphicsBeginImageContext(src.size);

    CGContextRef context = UIGraphicsGetCurrentContext();

    if (orientation == UIImageOrientationRight) {
        CGContextRotateCTM (context, radians(90));
    } else if (orientation == UIImageOrientationLeft) {
        CGContextRotateCTM (context, radians(-90));
    } else if (orientation == UIImageOrientationDown) {
        // NOTHING
    } else if (orientation == UIImageOrientationUp) {
        CGContextRotateCTM (context, radians(90));
    }

    [src drawAtPoint:CGPointMake(0, 0)];

    return UIGraphicsGetImageFromCurrentImageContext();
}

问题是它给了我一个空白的UIImage

以下是代码：-

UIImage *PortraitImage;
PortraitImage  = [[UIImage alloc] initWithCGImage: currentImage.CGImage
                                                    scale: 1.0
                                              orientation: UIImageOrientationLeft];

如果您想以某个特定角度旋转UIImage，则可以使用CIIFilter以任意角度旋转UIImage，但这在IOS 5.0中是可能的

CIImage *inputImage = [[CIImage alloc] initWithImage:[UIImage imageNamed:@"old-country-rain.jpg"]];
CIFilter *RotateFilter = [CIFilter filterWithName:@"CIStraightenFilter"];
[RotateFilter setValue:[NSNumber numberWithFloat: 1.04667f]  forKey:@"inputAngle"];
[RotateFilter setValue:inputImage forKey:kCIInputImageKey];
CIImage *displayImage = RotateFilter.outputImage;
UIImage *finalImage = [UIImage imageWithCIImage:displayImage];

---

我发现图像范围在旋转后不会改变。有什么建议吗？我的图像的displayImage.extents是640 x 480。旋转后，displayImage.extents仍为640 x 480。