一个简单的创建圆角图像的UIImage扩展实现

在iOS开发中经常需要用到圆角图像。简单搜索一下就能找到很多创建圆角图像的实现代码。我在 Stack Overflow 上找到了一段代码，略微修改了一下，写了个简单的Category方法，可以用来创建圆角图像。代码如下：

/* UIImage+RoundedRect.h*/ #import <UIKit/UIKit.h> @interface UIImage (RoundedCorner) - (UIImage *)roundedCornerImageWithCornerRadius:(CGFloat)cornerRadius; @end /* UIImage+RoundedRect.m*/ #import "UIImage+RoundedCorner.h" @implementation UIImage (RoundedCorner) - (UIImage *)roundedCornerImageWithCornerRadius:(CGFloat)cornerRadius { CGFloat w = self.size.width; CGFloat h = self.size.height; CGFloat scale = [UIScreen mainScreen].scale; // 防止圆角半径小于0，或者大于宽/高中较小值的一半。 if (cornerRadius < 0) cornerRadius = 0; else if (cornerRadius > MIN(w, h)) cornerRadius = MIN(w, h) / 2.; UIImage *image = nil; CGRect imageFrame = CGRectMake(0., 0., w, h); UIGraphicsBeginImageContextWithOptions(self.size, NO, scale); [[UIBezierPath bezierPathWithRoundedRect:imageFrame cornerRadius:cornerRadius] addClip]; [self drawInRect:imageFrame]; image = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext(); return image; } @end

把这个Category添加到项目中之后，直接对UIImage对象调用- roundedCornerImageWithCornerRadius:方法即可。以上实现并非最高效，最佳的实现，但是有时候Quick and Dirty的方法已经足够好了，是吧。（天音：你就自我安慰吧。）

#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 

+ (void)roundedImage:(UIImage *)image

          completion:(void (^)(UIImage *image))completion {

    dispatch_async( dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

        // Begin a new image that will be the new image with the rounded corners

        // (here with the size of an UIImageView)

        UIGraphicsBeginImageContextWithOptions(image.size, NO, image.scale);

        CGRect rect = CGRectMake(0, 0, image.size.width,image.size.height);

        

        // Add a clip before drawing anything, in the shape of an rounded rect

        [[UIBezierPath bezierPathWithRoundedRect:rect

                                    cornerRadius:image.size.width/2] addClip];

        // Draw your image

        [image drawInRect:rect];

        

        // Get the image, here setting the UIImageView image

        UIImage *roundedImage = UIGraphicsGetImageFromCurrentImageContext();

        

        // Lets forget about that we were drawing

        UIGraphicsEndImageContext();

        dispatch_async( dispatch_get_main_queue(), ^{

            if (completion) {

                completion(roundedImage);

            }

        });

    });

}