iOS UIImage剪辑到路径 [英] iOS UIImage clip to paths

问题描述

我正在处理用户使用UIBezierPath选择部分图像的图像。如何删除/清除/透明不属于该选择的所有内容？

I'm working with an image where the user has selected part of it using UIBezierPath. How can I delete/clear out/make transparent everything that is not part of that selection?

推荐答案

只需一条路径就可以轻松实现。只需将路径设置为剪切路径：

With one path it's very easy. Just set the path as the clipping path:

- (UIImage *)maskImage:(UIImage *)originalImage toPath:(UIBezierPath *)path {
    UIGraphicsBeginImageContextWithOptions(originalImage.size, NO, 0);
    [path addClip];
    [originalImage drawAtPoint:CGPointZero];
    UIImage *maskedImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return maskedImage;
}

如果你想使用多个路径的并集，那就更难了，因为Quartz没有任何直接计算两个路径的并集的函数。一种方法是逐个填充每个路径到一个掩码，然后通过掩码绘制图像：

If you want to use the union of multiple paths, it's harder, because Quartz doesn't have any functions that directly compute the union of two paths. One way is to fill each path one by one into a mask, and then draw the image through the mask:

- (UIImage *)maskedImage
{
    CGRect rect = CGRectZero;
    rect.size = self.originalImage.size;
    UIGraphicsBeginImageContextWithOptions(rect.size, YES, 0.0); {
        [[UIColor blackColor] setFill];
        UIRectFill(rect);
        [[UIColor whiteColor] setFill];
        for (UIBezierPath *path in self.paths)
            [path fill];
    }
    UIImage *mask = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    UIGraphicsBeginImageContextWithOptions(rect.size, NO, 0.0); {
        CGContextClipToMask(UIGraphicsGetCurrentContext(), rect, mask.CGImage);
        [self.originalImage drawAtPoint:CGPointZero];
    }
    UIImage *maskedImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return maskedImage;
}

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