iOS 学习 - 15.添加水印

绘制到位图

下面利用位图图形上下文给一个图片添加水印，在下面的程序中我们首先创建上下文，然后在上下文中绘制图片、直线和文本，最后从当前位图上下文中取得最终形成的新图片显示到界面

- (void)viewDidLoad {

    [super viewDidLoad];

    UIImage *image = [self drawImageAtImageContext];

    UIImageView *imageView = [[UIImageView alloc]initWithImage:image];

    imageView.center = CGPointMake(, );

    [self.view addSubview:imageView];

}

//添加水印

-(UIImage *)drawImageAtImageContext{

    //获得一个位图图形上下文

    CGSize size = CGSizeMake(, );//画布大小

    UIGraphicsBeginImageContext(size);

    UIImage *image = [UIImage imageNamed:@"[email protected]"];

    //注意绘图的位置是相对于画布顶点而言，不是屏幕

    [image drawInRect:CGRectMake(, , , )];

    //添加水印

    CGContextRef ref = UIGraphicsGetCurrentContext();

    //字符的长度和 font

    UIFont *font = [UIFont systemFontOfSize:];

    NSString *str = @"大金毛";

    int strLength = str.length *font.pointSize;

    //两点确定一条直线

    //下划线的长度等于字符长度

    CGContextMoveToPoint(ref, , );

    CGContextAddLineToPoint(ref, strLength + , );

    //直线的颜色、宽度

    [[UIColor redColor]setStroke];

    CGContextSetLineWidth(ref, );

    //绘制图像到指定图形上下文，只有边框

    CGContextDrawPath(ref, kCGPathStroke);

    //字符的位置

    [str drawInRect:CGRectMake(, , , ) withAttributes:@{NSFontAttributeName:font,NSForegroundColorAttributeName:[UIColor redColor]}];

    //返回绘制的新图形

    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();

    //最后一定不要忘了关闭上下文

    UIGraphicsEndImageContext();

    return newImage;

}

来自KenshinCui