为CAShapeLayer添加阴影，使内部保持透明 [英] Add a shadow to CAShapeLayer, so that the inside remains transparent

问题描述

我想为一个路径添加一个发光效果，就像它们有焦点时的蓝色光晕（OS X）界面元素一样。

I want to add a glow effect to a path, like the blue glow around (OS X) interface elements when they have focus.

我使用的是CAShapeLayer a（矩形）路径：

I used a CAShapeLayer with a (rectangular) path:

self.borderLayer = [CAShapeLayer layer];
CGPathRef path = CGPathCreateWithRect(self.bounds, NULL);
[self.borderLayer setPath:path];
CGPathRelease(path);

最后，这给了我一个带有边框的透明UIView。 （在我的具体情况下，它是带有附加动画的虚线，但这对于这个特定问题无关紧要）

In the end this gives me a transparent UIView with a border around it. (In my concrete case it's a dashed line with an additional animation, but that doesn't matter for this particular question)

我玩了CALayer的阴影属性，但它们总是填满整个图层。

I played around with the shadow properties of CALayer, but they will always fill the whole layer.

self.borderLayer.shadowPath = self.borderLayer.path;
self.borderLayer.shouldRasterize = YES;

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我想要的是只有UIViews周边线投下一个阴影，以便UIView的内部保持透明。

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What I want is that only the UIViews surrounding line drops a shadow, so that the inside of the UIView remains transparent.

推荐答案

我遇到类似的问题，看到我内心的阴影想要而不是发光。我用两个CALayers解决了这个问题。一，在代码中，背景为'_bg'（在我的情况下为黑色，不透明度为0.55）和白色边框。代码'_shadow'中的另一层具有清晰的背景并添加了发光效果。 _bg是_shadow图层的子视图。以下是相关代码：

I was having similar problems seeing the shadow inside where I wanted it instead of a glow. I solved it by using two CALayers. One, in the code, '_bg' for the background ( in my case black with opacity of 0.55) and a white border. The other layer, in the code '_shadow', has a clear background and adds the glow effect. _bg is a subview of the _shadow layer. Here's the relevant code:

_bg = [CALayer layer];
_shadow = [CALayer layer];

[self.layer insertSublayer:_shadow atIndex:0];
[_shadow addSublayer:_bg];

_bg.frame = self.bounds;
_bg.backgroundColor = [UIColor colorWithRed:0.0 green:0.0 blue:0.0 alpha:.55].CGColor;
_bg.cornerRadius=20.0;
_bg.borderColor=[UIColor whiteColor].CGColor;
_bg.borderWidth=2.0;

_shadow.frame=self.bounds;
_shadow.masksToBounds=NO;
_shadow.backgroundColor = [UIColor clearColor].CGColor;
_shadow.cornerRadius=3.0;
_shadow.shadowRadius=3.0;
_shadow.shadowColor=[UIColor whiteColor].CGColor;
_shadow.shadowOpacity=0.6;
_shadow.shadowOffset=CGSizeMake(0.0, 0.0);

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