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图像中的 CGPath

发布于 2024-12-20 08:53:38 字数 296 浏览 2 评论 0原文

我需要根据图像（任何可能的形状）创建蒙版。我需要：

使用 CGPath 创建 CALayer 作为适当的掩码
调用 [UIView.layer setMask: with layer above ]

所以主要的大问题是如何根据黑白图像设置 CGPath？或者是否可以直接从图像放置遮罩？

谢谢！

面具的示例图像：示例掩码

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千里故人稀 2024-12-27 08:53:38

您需要创建带有 Alpha 通道的图像。根据 CALayer 的 mask 属性文档：

一个可选层，其 alpha 通道用作遮罩来选择
图层背景和合成结果之间
图层的内容及其过滤后的背景。

因此，您想要用作遮罩的图层需要一个 Alpha 通道。如果你想使用图像来创建这样的通道，图像本身需要有一个 Alpha 通道。因此，您需要将上面发布的黑白蒙版复制到图像的 Alpha 通道中。该特定图像的颜色将被忽略。然后加载图像，为其设置图层内容并将该图层用作不同的图层蒙版。与此相关的事情：

UIImage* imageWithAlphaChannel = [UIImage imageNamed:@"alpha.png"]; // Won't work with jpg
CGImageRef cgImageWithAlpha = [imageWithAlphaChannel CGImage];
CALayer* maskingLayer = [CALayer layer];
maskingLayer.contents = (id)cgImageWithAlpha;

//Assume viewToBeMasked is the view, who's layer needs to be masked
CALayer* layerToBeMasked = viewToBeMasked.layer;
layerToBeMasked.mask = maskingLayer;
maskingLayer.frame = layerToBeMasked.bounds;
//Alternativly use: viewToBeMasked.layer.mask = maskingLayer;

在浏览器中编码，请原谅系统错误。

将所有蒙版存储为 png 文件可能会增大应用程序的大小。您可以将蒙版存储为 jpg，并在运行时使用 CoreGraphics 绘图函数创建适当的 alpha 版本。但这是另一个问题了......

You will need to create your image with an alpha channel. According to CALayer's mask property documentation:

An optional layer whose alpha channel is used as a mask to select
between the layer's background and the result of compositing the
layer's contents with its filtered background.

So the layer you want to use as mask needs an alpha channel. If you want to use an image to create such a channel, the image itself needs to have an alpha channel. So you would need to copy the black and white mask you posted above into the alpha channel of an image. The color of that particular image is ignored. You then load the image, set a layers contents to it and use that layer as a different layers mask. Something around this:

UIImage* imageWithAlphaChannel = [UIImage imageNamed:@"alpha.png"]; // Won't work with jpg
CGImageRef cgImageWithAlpha = [imageWithAlphaChannel CGImage];
CALayer* maskingLayer = [CALayer layer];
maskingLayer.contents = (id)cgImageWithAlpha;

//Assume viewToBeMasked is the view, who's layer needs to be masked
CALayer* layerToBeMasked = viewToBeMasked.layer;
layerToBeMasked.mask = maskingLayer;
maskingLayer.frame = layerToBeMasked.bounds;
//Alternativly use: viewToBeMasked.layer.mask = maskingLayer;

Coded in the browser, excuse systactical errors.

Storing all your masks as png files might blow your app size. You could store the masks as jpgs and create the appropriate alpha version at runtime using the CoreGraphics drawing functions. But that is another question.....

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