如何设置图片四个方向圆角属性

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



如何实现画四个方向的弧线呢？

先看看示意图



头文件

#import <Foundation/Foundation.h>

typedef enum {

UIImageRoundedCornerTopLeft = 1,

UIImageRoundedCornerTopRight = 1 << 1,

UIImageRoundedCornerBottomRight = 1 << 2,

UIImageRoundedCornerBottomLeft = 1 << 3

} UIImageRoundedCorner;

@interface UIImage (Utility)

//+ (void)addRoundedRectToPath(CGContextRef context, CGRect rect, float radius, UIImageRoundedCorner cornerMask);

- (UIImage *)roundedRectWith:(float)radius cornerMask:(UIImageRoundedCorner)cornerMask;

@end

实现文件

#import "UIImage+Utility.h"

//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);
}

@implementation UIImage (Utility)
- (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 = [UIImage imageWithCGImage:imageMasked];

CGImageRelease(imageMasked);

return newImage;
}
@end

实现方法如下：

- (IBAction)showRectImage

{

UIImage *rectImage = [UIImage imageNamed:@"test.jpg"];

self.imageView.image = rectImage;

}

- (IBAction)showRoundImage

{

UIImage *rectImage = [UIImage imageNamed:@"test.jpg"];

UIImage *roundImage = [rectImage roundedRectWith:100

cornerMask:UIImageRoundedCornerBottomLeft|UIImageRoundedCornerBottomRight|UIImageRoundedCornerTopLeft|UIImageRoundedCornerTopRight];

self.imageView.image = roundImage;

}

- (IBAction)show2RoundImage

{

UIImage *rectImage = [UIImage imageNamed:@"test.jpg"];

UIImage *round2Image = [rectImage roundedRectWith:100

cornerMask:UIImageRoundedCornerBottomLeft|UIImageRoundedCornerBottomRight];

self.imageView.image = round2Image;

}

对于四个角，用下面的角进行逻辑或的方法。

UIImageRoundedCornerTopRight
UIImageRoundedCornerTopLeft
UIImageRoundedCornerBottomRight

UIImageRoundedCornerBottomLeft

项目文件下载

参考URL
http://stackoverflow.com/questions/4847163/round-two-corners-in-uiview http://stackoverflow.com/questions/4845211/just-two-rounded-corners http://blog.sallarp.com/iphone-uiimage-round-corners/