在保留alpha的同时从阴影视图创建UIImage？ [英] Create UIImage from shadowed view while retaining alpha?

问题描述

我有一个不寻常的问题。在我的应用程序中，我使用基本的Quartz2d图层阴影来遮蔽 UIImageView 。这是我的代码：

I have a somewhat unusual problem. In my app, I am shadowing a UIImageView using basic Quartz2d layer shadowing. Here's my code:

imageView.layer.shadowOpacity = 1.0; // Pretty self explanatory
imageView.layer.shadowRadius = 8.0; // My softness
imageView.layer.shadowColor = [UIColor blackColor].CGColor; // Color of the shadow
imageView.layer.shadowOffset = CGSizeMake(0.0, 0.0); // Offset of the shadow

这会在图像视图后面产生很好的模糊效果。但是，我正在使用此视图进行一些动画，并且在过渡期间不断重新计算阴影会导致非常不稳定的过渡。我希望能够做的是从图像视图创建一个UIImage或.png文件，其中模糊和alpha完整。这是我已经尝试过的：

This produces a nice blur behind the image view. However, I am doing some animation with this view, and the constant recalculation of the shadowing during the transitions causes a very choppy transition. What I'd like to be able to do is create a UIImage or .png file out of the image view with the blur and its alpha intact. Here's what I've already tried:

UIGraphicsBeginImageContext(CGSizeMake(320, 396)); 
[imageView.layer renderInContext:UIGraphicsGetCurrentContext()]; 
UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
UIImageWriteToSavedPhotosAlbum(viewImage, nil, nil, nil);

由于我有一个阴影在图像视图之外，我不能只是通过他在 UIGraphicsBeginImageContext 函数中的大小。我设置了正确的大小，但结果图像不保存我的alpha，而是在阴影后面放置一个白色背景，这对我不起作用，因为我的真实背景是木质纹理。此外，视图不会在结果文件中居中。

Since I have a shadow which "grows outside" of the image view, I can't just pass his size in the UIGraphicsBeginImageContext function. I set the correct size, but the resulting image doesn't save my alpha, instead it places a white background behind the shadow, which won't work for me because my real background is a wood texture. Also, the view isn't centered in the resulting file.

我对 UIKit 非常满意，但是我是一个真正的noobie与 Quartz 2D图形，所以如果有一个明显的答案，无论如何发送它。 ：）

I'm pretty good with UIKit, but I'm a real noobie with Quartz 2d graphics, so if there's an obvious answer to this, send it anyway. :)

推荐答案

尝试设置 UIImageView 的 backgroundColor 到 [UIColor clearColor] - 这可以使您当前的解决方案正常工作。

Try setting your UIImageView's backgroundColor to [UIColor clearColor] - this may enable your current solution to work.

imageView.backgroundColor = [UIColor clearColor];
UIGraphicsBeginImageContext(CGSizeMake(320, 396)); 
[imageView.layer renderInContext:UIGraphicsGetCurrentContext()]; 
UIImage *viewImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

资料来源：在CoreGraphics iphone中将CGLayer转换为*透明* UIImage和PNG文件

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