图片截取

- (UIImage*)getSubImage:(UIImage *)image mCGRect:(CGRect)mCGRect
             centerBool:(BOOL)centerBool{
    /*如若centerBool为Yes则是由中心点取mCGRect范围的图片*/
    float imgWidth = image.size.width;
    float imgHeight = image.size.height;
    float viewWidth = mCGRect.size.width;
    float viewHidth = mCGRect.size.height;
    CGRect rect;
    if(centerBool){
        rect = CGRectMake((imgWidth-viewWidth)/2,(imgHeight-viewHidth)/2,viewWidth,viewHidth);
    }else{
        if(viewHidth < viewWidth){
            if(imgWidth <= imgHeight){
                rect = CGRectMake(0, 0, imgWidth, imgWidth*imgHeight/viewWidth);
            }else{
                float width = viewWidth*imgHeight/viewHidth;
                float x = (imgWidth - width)/2;
                if(x > 0){
                    rect = CGRectMake(x, 0, width, imgHeight);
                }else{
                    rect = CGRectMake(0, 0, imgWidth, imgWidth*viewHidth/viewWidth);
                }
            }
        }else{
            if(imgWidth <= imgHeight){
                float height = viewHidth*imgWidth/viewWidth;
                if(height < imgHeight){
                    rect = CGRectMake(0,0, imgWidth, height);
                }else{
                    rect = CGRectMake(0,0, viewWidth*imgHeight/viewHidth,imgHeight);
                }
            }else{
                float width = viewWidth * imgHeight / viewHidth;
                if(width < imgWidth){
                    float x = (imgWidth - width)/2;
                    rect = CGRectMake(x,0,width, imgHeight);
                }else{
                    rect = CGRectMake(0,0,imgWidth, imgHeight);
                }
            }
        }
    }
    
    CGImageRef subImageRef = CGImageCreateWithImageInRect(image.CGImage, rect);
    CGRect smallBounds = CGRectMake(0,0,CGImageGetWidth(subImageRef),CGImageGetHeight(subImageRef));
    
    UIGraphicsBeginImageContext(smallBounds.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextDrawImage(context, smallBounds, subImageRef);
    UIImage *smallImage = [UIImage imageWithCGImage:subImageRef];
    UIGraphicsEndImageContext();
    
    return smallImage;
}