iOS将image转90,180,270度的方法

http://blog.sina.com.cn/s/blog_6602ffbc0101ckx3.html

这里要分享的是将image旋转，而不是将imageView旋转，原理就是使用quartz2D来画图片，然后使用ctm变幻来实现旋转。

注：quartz2D的绘图左边和oc里面的绘图左边不一样，导致绘画出的图片是反转的。所以一上来得使它转正再进行进一步的旋转等

+ (UIImage *)image:(UIImage *)image rotation:(UIImageOrientation)orientation

{

long double rotate = 0.0;

CGRect rect;

float translateX = 0;

float translateY = 0;

float scaleX = 1.0;

float scaleY = 1.0;

switch (orientation) {

case UIImageOrientationLeft:

rotate = M_PI_2;

rect = CGRectMake(0, 0, image.size.height, image.size.width);

translateX = 0;

translateY = -rect.size.width;

scaleY = rect.size.width/rect.size.height;

scaleX = rect.size.height/rect.size.width;

break;

case UIImageOrientationRight:

rotate = 3 * M_PI_2;

rect = CGRectMake(0, 0, image.size.height, image.size.width);

translateX = -rect.size.height;

translateY = 0;

scaleY = rect.size.width/rect.size.height;

scaleX = rect.size.height/rect.size.width;

break;

case UIImageOrientationDown:

rotate = M_PI;

rect = CGRectMake(0, 0, image.size.width, image.size.height);

translateX = -rect.size.width;

translateY = -rect.size.height;

break;

default:

rotate = 0.0;

rect = CGRectMake(0, 0, image.size.width, image.size.height);

translateX = 0;

translateY = 0;

break;

}

UIGraphicsBeginImageContext(rect.size);

CGContextRef context = UIGraphicsGetCurrentContext();

//做CTM变换

CGContextTranslateCTM(context, 0.0, rect.size.height);

CGContextScaleCTM(context, 1.0, -1.0);

CGContextRotateCTM(context, rotate);

CGContextTranslateCTM(context, translateX, translateY);

CGContextScaleCTM(context, scaleX, scaleY);

//绘制图片

CGContextDrawImage(context, CGRectMake(0, 0, rect.size.width, rect.size.height), image.CGImage);

UIImage *newPic = UIGraphicsGetImageFromCurrentImageContext();

return newPic;

}