oc 高效绘制圆角

oc_draw_image_corner.codesnippest

- (UIImage*)lj_imageAddCornerWithRadius:(CGFloat)radius byRoundingCorners:(UIRectCorner)corners borderWidth:(CGFloat)borderWidth borderColor:(UIColor *)borderColor imageSize:(CGSize)size {
    
    // 1. 创建一个画布
    CGRect rect = CGRectMake(0, 0, size.width, size.height);
    UIGraphicsBeginImageContextWithOptions(size, NO, [UIScreen mainScreen].scale);
    // 2. 获取图形上下文
    CGContextRef ctx = UIGraphicsGetCurrentContext();
    // 3. 计算 path  圆角
    UIBezierPath * path = [UIBezierPath bezierPathWithRoundedRect:rect byRoundingCorners:corners cornerRadii:CGSizeMake(radius, radius)];
    CGContextAddPath(ctx,path.CGPath);
    CGContextClip(ctx);
    
    // 绘制出图片
    [self drawInRect:rect];
    
    // 4. 添加 border
    if (borderWidth > 0 && borderColor) {
        CGContextSaveGState(ctx);
        [borderColor setStroke];
        path.lineWidth = borderWidth;
        [path stroke];
        CGContextRestoreGState(ctx);
    }
    
    // 获取图片
    UIImage * newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}