自己对这个进行了重新封装，方便大家使用。
//
// UIImage+RoundRect.h
//
// Created by Eric on 11/11/12.
// Copyright (c) 2012 Saick. All rights reserved.
//
#import<UIKit/UIKit.h>
#import "SQLibs.h"
typedefenum {
UIImageRoundedCornerTopLeft = 1,
UIImageRoundedCornerTopRight = 1 <<1,
UIImageRoundedCornerBottomRight = 1 <<2,
UIImageRoundedCornerBottomLeft = 1 <<3
}UIImageRoundedCorner;
@interface UIImage(RoundRect)
-(UIImage*)roundedRectWith:(float)radius;
-(UIImage*)roundedRectWith:(float)radius cornerMask:(UIImageRoundedCorner)cornerMask;
@end
//
// UIImage+RoundRect.m
//
// Created by Eric on 11/11/12.
// Copyright (c) 2012 Saick. All rights reserved.
//
#import"UIImage+RoundRect.h"
@implementation UIImage(RoundRect)
//UIKit坐标系统原点在左上角，y方向向下的（坐标系A），但在Quartz中坐标系原点在左下角，y方向向上的(坐标系B)。图片绘制也是颠倒的。
static void addRoundedRectToPath(CGContextRef context, CGRect rect, float radius, UIImageRoundedCorner cornerMask)
{
//原点在左下方，y方向向上。移动到线条2的起点。
CGContextMoveToPoint(context,rect.origin.x, rect.origin.y + radius);
//画出线条2, 目前画线的起始点已经移动到线条2的结束地方了。
CGContextAddLineToPoint(context,rect.origin.x, rect.origin.y + rect.size.height - radius);
//如果左上角需要画圆角，画出一个弧线出来。
if (cornerMask &UIImageRoundedCornerTopLeft){
//已左上的正方形的右下脚为圆心，半径为radius， 180度到90度画一个弧线，
CGContextAddArc(context, rect.origin.x + radius, rect.origin.y + rect.size.height - radius,
radius, M_PI,M_PI / 2, 1);
}
else {
//如果不需要画左上角的弧度。从线2终点，画到线3的终点，
CGContextAddLineToPoint(context,rect.origin.x, rect.origin.y + rect.size.height);
//线3终点，画到线4的起点
CGContextAddLineToPoint(context,rect.origin.x + radius, rect.origin.y + rect.size.height);
}
//画线4的起始，到线4的终点
CGContextAddLineToPoint(context,rect.origin.x + rect.size.width - radius,
rect.origin.y + rect.size.height);
//画右上角
if (cornerMask &UIImageRoundedCornerTopRight){
CGContextAddArc(context, rect.origin.x + rect.size.width - radius,
rect.origin.y + rect.size.height - radius, radius, M_PI / 2, 0.0f, 1);
}
else {
CGContextAddLineToPoint(context,rect.origin.x + rect.size.width, rect.origin.y + rect.size.height);
CGContextAddLineToPoint(context,rect.origin.x + rect.size.width, rect.origin.y + rect.size.height - radius);
}
CGContextAddLineToPoint(context,rect.origin.x + rect.size.width, rect.origin.y + radius);
//画右下角弧线
if (cornerMask &UIImageRoundedCornerBottomRight){
CGContextAddArc(context, rect.origin.x + rect.size.width - radius, rect.origin.y + radius,
radius, 0.0f,-M_PI / 2, 1);
}
else {
CGContextAddLineToPoint(context,rect.origin.x + rect.size.width, rect.origin.y);
CGContextAddLineToPoint(context,rect.origin.x + rect.size.width - radius, rect.origin.y);
}
CGContextAddLineToPoint(context,rect.origin.x + radius, rect.origin.y);
//画左下角弧线
if (cornerMask &UIImageRoundedCornerBottomLeft){
CGContextAddArc(context, rect.origin.x + radius, rect.origin.y + radius, radius,
-M_PI /2, M_PI, 1);
}
else {
CGContextAddLineToPoint(context,rect.origin.x, rect.origin.y);
CGContextAddLineToPoint(context,rect.origin.x, rect.origin.y + radius);
}
CGContextClosePath(context);
}
-(UIImage*)roundedRectWith:(float)radius
{
return [selfroundedRectWith:radius cornerMask:UIImageRoundedCornerBottomLeft|UIImageRoundedCornerBottomRight | UIImageRoundedCornerTopLeft | UIImageRoundedCornerTopRight];
}
-(UIImage*)roundedRectWith:(float)radius cornerMask:(UIImageRoundedCorner)cornerMask
{
UIImageView*bkImageViewTmp = [[[UIImageView alloc] initWithImage:self] autorelease];
int w = self.size.width;
int h = self.size.height;
CGColorSpaceRef colorSpace =CGColorSpaceCreateDeviceRGB();
CGContextRef context =CGBitmapContextCreate(NULL,w, h, 8, 4* w, colorSpace,kCGImageAlphaPremultipliedFirst);
CGContextBeginPath(context);
addRoundedRectToPath(context,bkImageViewTmp.frame,radius, cornerMask);
CGContextClosePath(context);
CGContextClip(context);
CGContextDrawImage(context, CGRectMake(0, 0,w, h), self.CGImage);
CGImageRef imageMasked= CGBitmapContextCreateImage(context);
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);
UIImage *newImage = [UIImageimageWithCGImage:imageMasked];
CGImageRelease(imageMasked);
return newImage;
}
@end
转自http://www.cnblogs.com/likwo/archive/2011/06/16/2082781.html
一般图片圆角显示都是四个角都显示圆角，如果只有这个功能需求，采用常用的方法就可以了，也不用费那么多事情。但是在有些情况下需要只显示图片的2个圆角，就不太好实现了。
先看效果图 ，未做圆角转换的图片
做了4个角的圆角转换的图片
只做了下面2个圆角转换的图片
