將圖片旋轉（這裡不是旋轉imageView）

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

原理就是使用quartz2D來畫圖片，然後使用ctm變幻來實現旋轉。 注：quartz2D的繪圖左邊和oc裡面的繪圖左邊不一樣，導致繪畫出的圖片是反轉的。所以一上來得使它轉正再進行進一步的旋轉等。 //將圖片旋轉90，180，270度的方法

• (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變換 CGContextTranslateCTM(context, 0.0, rect.size.height); CGContextScaleCTM(context, 1.0, -1.0); CGContextRotateCTM(context, rotate); CGContextTranslateCTM(context, translateX, translateY);

  CGContextScaleCTM(context, scaleX, scaleY); //繪製圖片 CGContextDrawImage(context, CGRectMake(0, 0, rect.size.width, rect.size.height), image.CGImage);

  UIImage *newPic = UIGraphicsGetImageFromCurrentImageContext();

  return newPic; }