UIImage+wiRoundedRectImage.h

#import <UIKit/UIKit.h>

@interface UIImage (wiRoundedRectImage)

+ (id)createRoundedRectImage:(UIImage*)image size:(CGSize)size radius:(NSInteger)r;

@end

UIImage+wiRoundedRectImage.m

#import "UIImage+wiRoundedRectImage.h"

@implementation UIImage (wiRoundedRectImage)

 
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 radius:(NSInteger)r
{
    // 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, r, r);
    CGContextClosePath(context);
    CGContextClip(context);
    CGContextDrawImage(context, CGRectMake(0, 0, w, h), img.CGImage);
    CGImageRef imageMasked = CGBitmapContextCreateImage(context);
    img = [UIImage imageWithCGImage:imageMasked];
    
    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);
    CGImageRelease(imageMasked);
    
    return img;
}

@end

呼叫方法:

    UIImage * image = [UIImageimageNamed:@"123.jpg"];  // 設定原圖

    CGSize size = CGSizeMake(100,100);  // 設定尺寸

    _pImgV.image = [UIImagecreateRoundedRectImage:image size:size radius:10];   // 設定radius

轉自：http://www.cnblogs.com/thefeelingofsimple/archive/2013/02/20/2918547.html