给UIImage添加圆角，也可用于CCSprite//给图片添加圆角显示
- (UIImage *) roundCorners: (UIImage*) img
{int w = img.size.width;int h = img.size.height;CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();CGContextRef context = CGBitmapContextCreate(NULL, w, h, 8, 4 * w, colorSpace, kCGImageAlphaPremultipliedFirst);CGContextBeginPath(context);CGRect rect = CGRectMake(0, 0, img.size.width, img.size.height);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);[img release];return [UIImage imageWithCGImage:imageMasked];
}//这是被调用的静态方法
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);CGContextAddArcToPoint(context, fw, fh, fw/2, fh, 1);CGContextAddArcToPoint(context, 0, fh, 0, fh/2, 1);CGContextAddArcToPoint(context, 0, 0, fw/2, 0, 1);CGContextAddArcToPoint(context, fw, 0, fw, fh/2, 1);CGContextClosePath(context);CGContextRestoreGState(context);
}

经测验，可以正常使用。