图片旋转加图上圆角

    在作通信录页面的时候，头像须要圆角显示，使用layer的方式虽然也能够实现可是会比较卡。因此找了另一种方法，可是也有个问题是，用户横着手机拍照的照片作头像的话，会被自动旋转，虽然也有相应的方法解决，可是太慢了，旋转一张图片须要1.2秒左右。不知道有没有高手能够解决这个问题。另外想到一种办法，可是还没试的，就是在gcd里面使用layer的方法给UImageView画圆角，不知道这样是否有风险。

UIView加圆角会卡的解决办法

作iOS开发的时候有可能常常碰到莫名其妙的滑动不畅（在UIScrollView以及其子类）或者在navigation切换的时候不畅的问题，这颇有多是在界面中加了太多带圆角而且masksToBounds为YES的UIView而引发的。 

暂时全部版本的api都没有解决这个问题。所以若是想要避免这个问题，只能放弃在UIView上加圆角，若是该View是用来显示图片的，则能够将该UIView上的图片自己加圆角。 

1. static void addRoundedRectToPath(CGContextRef context, CGRect rect, float ovalWidth,  
                                    float ovalHeight)  
   {  
       float fw, fh;  
       if (ovalWidth == 0 || ovalHeight == 0) {  
           CGContextAddRect(context, rect);  
           return;  
       }  
       CGContextSaveGState(context);  
       CGContextTranslateCTM(context, CGRectGetMinX(rect), CGRectGetMinY(rect));  
       CGContextScaleCTM(context, ovalWidth, ovalHeight);  
       fw = CGRectGetWidth(rect) / ovalWidth;  
       fh = CGRectGetHeight(rect) / ovalHeight;  
       CGContextMoveToPoint(context, fw, fh/2);  // Start at lower right corner  
       CGContextAddArcToPoint(context, fw, fh, fw/2, fh, 1);  // Top right corner  
       CGContextAddArcToPoint(context, 0, fh, 0, fh/2, 1); // Top left corner  
       CGContextAddArcToPoint(context, 0, 0, fw/2, 0, 1); // Lower left corner  
       CGContextAddArcToPoint(context, fw, 0, fw, fh/2, 1); // Back to lower right  
       CGContextClosePath(context);  
       CGContextRestoreGState(context);  
   }  
     
   + (id) createRoundedRectImage:(UIImage*)image size:(CGSize)size  
   {  
       // the size of CGContextRef  
       int w = size.width;  
       int h = size.height;  
         
       UIImage *img = image;  
       CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();  
       CGContextRef context = CGBitmapContextCreate(NULL, w, h, 8, 4 * w, colorSpace, kCGImageAlphaPremultipliedFirst);  
       CGRect rect = CGRectMake(0, 0, w, h);  
       CGContextBeginPath(context);  
       addRoundedRectToPath(context, rect, 10, 10);  
       CGContextClosePath(context);  
       CGContextClip(context);  
       CGContextDrawImage(context, CGRectMake(0, 0, w, h), img.CGImage);  
       CGImageRef imageMasked = CGBitmapContextCreateImage(context);  
       CGContextRelease(context);  
       CGColorSpaceRelease(colorSpace);  
       return [UIImage imageWithCGImage:imageMasked];  
   }

将UIView上的图片用该方法处理一次，就能够得到带了圆角的图片了。

解决UIImage图片旋转

iOS程序中使用系统相机拍照和从相册选取图片，直接上传后在非mac系统下看到的图片会发生旋转的现象，那是由于咱们没有经过图片的旋转属性修改图片倒置的。下面的方法能够很简单的解决旋转问题：

@interface UIImage (fixOrientation) - (UIImage *)fixOrientation; @end @implementation UIImage (fixOrientation) - (UIImage *)fixOrientation { // No-op if the orientation is already correct if (self.imageOrientation == UIImageOrientationUp) return self; // We need to calculate the proper transformation to make the image upright. // We do it in 2 steps: Rotate if Left/Right/Down, and then flip if Mirrored. CGAffineTransform transform = CGAffineTransformIdentity; switch (self.imageOrientation) { case UIImageOrientationDown: case UIImageOrientationDownMirrored: transform = CGAffineTransformTranslate(transform, self.size.width, self.size.height); transform = CGAffineTransformRotate(transform, M_PI); break; case UIImageOrientationLeft: case UIImageOrientationLeftMirrored: transform = CGAffineTransformTranslate(transform, self.size.width, 0); transform = CGAffineTransformRotate(transform, M_PI_2); break; case UIImageOrientationRight: case UIImageOrientationRightMirrored: transform = CGAffineTransformTranslate(transform, 0, self.size.height); transform = CGAffineTransformRotate(transform, -M_PI_2); break; } switch (self.imageOrientation) { case UIImageOrientationUpMirrored: case UIImageOrientationDownMirrored: transform = CGAffineTransformTranslate(transform, self.size.width, 0); transform = CGAffineTransformScale(transform, -1, 1); break; case UIImageOrientationLeftMirrored: case UIImageOrientationRightMirrored: transform = CGAffineTransformTranslate(transform, self.size.height, 0); transform = CGAffineTransformScale(transform, -1, 1); break; } // Now we draw the underlying CGImage into a new context, applying the transform // calculated above. CGContextRef ctx = CGBitmapContextCreate(NULL, self.size.width, self.size.height, CGImageGetBitsPerComponent(self.CGImage), 0, CGImageGetColorSpace(self.CGImage), CGImageGetBitmapInfo(self.CGImage)); CGContextConcatCTM(ctx, transform); switch (self.imageOrientation) { case UIImageOrientationLeft: case UIImageOrientationLeftMirrored: case UIImageOrientationRight: case UIImageOrientationRightMirrored: // Grr... CGContextDrawImage(ctx, CGRectMake(0,0,self.size.height,self.size.width), self.CGImage); break; default: CGContextDrawImage(ctx, CGRectMake(0,0,self.size.width,self.size.height), self.CGImage); break; } // And now we just create a new UIImage from the drawing context CGImageRef cgimg = CGBitmapContextCreateImage(ctx); UIImage *img = [UIImage imageWithCGImage:cgimg]; CGContextRelease(ctx); CGImageRelease(cgimg); return img; } @end