iOS-利用贝塞尔曲线设置圆角

/**
 裁剪图片
 
 @param radius 半径
 @param corners 角
 @param borderWidth 线宽值大于矩形的一半宽度或高度夹适当宽度的一半或高度。
 @param borderColor 线颜色
 @param borderLineJoin 线转交类型
 @return iamge
 */
- (UIImage *)imageByRoundCornerRadius:(CGFloat)radius
                              corners:(UIRectCorner)corners
                          borderWidth:(CGFloat)borderWidth
                          borderColor:(UIColor *)borderColor
                       borderLineJoin:(CGLineJoin)borderLineJoin {
    
    // 判断传入的角是哪种
    if (corners != UIRectCornerAllCorners) {
        UIRectCorner tmp = 0;
        if (corners & UIRectCornerTopLeft) tmp |= UIRectCornerBottomLeft;
        if (corners & UIRectCornerTopRight) tmp |= UIRectCornerBottomRight;
        if (corners & UIRectCornerBottomLeft) tmp |= UIRectCornerTopLeft;
        if (corners & UIRectCornerBottomRight) tmp |= UIRectCornerTopRight;
        corners = tmp;
    }
    
    UIGraphicsBeginImageContextWithOptions(self.size, NO, self.scale);
    // 获取当前上下文
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGRect rect = CGRectMake(0, 0, self.size.width, self.size.height);
    // 缩放因子设置为x=1 y= -1
    CGContextScaleCTM(context, 1, -1);
    // 修改xy值，x不变 y上移rect.size.height高度
    CGContextTranslateCTM(context, 0, -rect.size.height);
    
    CGFloat minSize = MIN(self.size.width, self.size.height);
    
    // 当线宽小于 长宽之间较小的那个的一半的时候 利用UIBezierPath裁剪出需要的范围
    if (borderWidth < minSize / 2) {
        UIBezierPath *path = [UIBezierPath bezierPathWithRoundedRect:CGRectInset(rect, borderWidth, borderWidth) byRoundingCorners:corners cornerRadii:CGSizeMake(radius, borderWidth)];
        [path closePath];
        
        CGContextSaveGState(context);
        // 裁剪
        [path addClip];
        CGContextDrawImage(context, rect, self.CGImage);
        CGContextRestoreGState(context);
    }
    
    // 下面判断都满足的情况下去绘制边框线
    if (borderColor && borderWidth < minSize / 2 && borderWidth > 0) {
        CGFloat strokeInset = (floor(borderWidth * self.scale) + 0.5) / self.scale;
        CGRect strokeRect = CGRectInset(rect, strokeInset, strokeInset);
        CGFloat strokeRadius = radius > self.scale / 2 ? radius - self.scale / 2 : 0;
        UIBezierPath *path = [UIBezierPath bezierPathWithRoundedRect:strokeRect byRoundingCorners:corners cornerRadii:CGSizeMake(strokeRadius, borderWidth)];
        [path closePath];
        
        path.lineWidth = borderWidth;
        path.lineJoinStyle = borderLineJoin;
        [borderColor setStroke];
        [path stroke];
    }
    
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return image;
}

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